Chore: Java 21.

.drone.yml

@@ -3,7 +3,7 @@ type: docker
 name: default
 steps:
   - name: build
-    image: maven:3.8-openjdk-18-slim
+    image: maven:3.9-eclipse-temurin-21
     commands:
       - mvn clean install -DskipTests=true -Dmaven.javadoc.skip=true -B -V
     when:
@@ -13,7 +13,7 @@ steps:
           - refs/head/feature/**
           - refs/tags/**
   - name: test
-    image: maven:3.8-openjdk-18-slim
+    image: maven:3.9-eclipse-temurin-21
     commands:
       - mvn test -B
     when:
@@ -22,7 +22,7 @@ steps:
           - master
           - feature/*
   - name: deploy
-    image: maven:3.8-openjdk-18-slim
+    image: maven:3.9-eclipse-temurin-21
     environment:
       REPO_TOKEN:
         from_secret: repo-token

pom.xml

@@ -46,7 +46,6 @@
         <tag>HEAD</tag>
     </scm>
 
-
     <distributionManagement>
         <snapshotRepository>
             <id>ossrh</id>
@@ -56,16 +55,22 @@
     </distributionManagement>
 
     <properties>
-        <jackson.version>2.15.0</jackson.version>
+        <assertj.version>3.25.3</assertj.version>
+        <jackson.version>2.17.1</jackson.version>
         <jsonschema2pojo-maven-plugin.version>1.2.1</jsonschema2pojo-maven-plugin.version>
+        <logback.version>1.5.6</logback.version>
+        <lombok.version>1.18.32</lombok.version>
+        <maven.compiler.release>21</maven.compiler.release>
         <maven-site-plugin.version>4.0.0-M8</maven-site-plugin.version>
-        <pdfbox.version>2.0.28</pdfbox.version>
+        <pdfbox.version>3.0.2</pdfbox.version>
+        <slf4j.version>2.0.12</slf4j.version>
     </properties>
 
     <dependencies>
         <dependency>
             <groupId>org.projectlombok</groupId>
             <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
         </dependency>
         <dependency>
             <groupId>org.jetbrains</groupId>
@@ -107,7 +112,7 @@
         <dependency>
             <groupId>org.assertj</groupId>
             <artifactId>assertj-core</artifactId>
-            <version>3.24.2</version>
+            <version>${assertj.version}</version>
             <scope>test</scope>
         </dependency>
     </dependencies>

src/main/java/ch/fritteli/maze/generator/Main.java

@@ -9,17 +9,18 @@ import ch.fritteli.maze.generator.renderer.jsonfile.JsonFileRenderer;
 import ch.fritteli.maze.generator.renderer.pdffile.PDFFileRenderer;
 import ch.fritteli.maze.generator.renderer.text.TextRenderer;
 import ch.fritteli.maze.generator.renderer.textfile.TextFileRenderer;
-import java.nio.file.Path;
-import java.nio.file.Paths;
-import lombok.NonNull;
 import lombok.experimental.UtilityClass;
 import lombok.extern.slf4j.Slf4j;
+import org.jetbrains.annotations.NotNull;
+
+import java.nio.file.Path;
+import java.nio.file.Paths;
 
 @Slf4j
 @UtilityClass
 public class Main {
 
-    public static void main(@NonNull final String[] args) {
+    public static void main(@NotNull final String[] args) {
         final int width = 20;
         final int height = 30;
         final Maze maze = new Maze(width, height/*, 0*/);
@@ -58,7 +59,7 @@ public class Main {
         log.info("PDF rendering to file:\n{}", pdfFileRenderer.render(maze));
     }
 
-    private static String getBaseFilename(@NonNull final Maze maze) {
+    private static String getBaseFilename(@NotNull final Maze maze) {
         return "maze-" + maze.getWidth() + "x" + maze.getHeight() + "-" + maze.getRandomSeed();
     }
 }

src/main/java/ch/fritteli/maze/generator/algorithm/RandomDepthFirst.java

@@ -5,21 +5,22 @@ import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.model.Position;
 import ch.fritteli.maze.generator.model.Tile;
 import io.vavr.control.Option;
+import org.jetbrains.annotations.NotNull;
+
 import java.util.Deque;
 import java.util.LinkedList;
 import java.util.Random;
-import lombok.NonNull;
 
 public class RandomDepthFirst {
 
-    @NonNull
+    @NotNull
     private final Maze maze;
-    @NonNull
+    @NotNull
     private final Random random;
-    @NonNull
+    @NotNull
     private final Deque<Position> positions = new LinkedList<>();
 
-    public RandomDepthFirst(@NonNull final Maze maze) {
+    public RandomDepthFirst(@NotNull final Maze maze) {
         this.maze = maze;
         this.random = new Random(maze.getRandomSeed());
     }
@@ -34,16 +35,16 @@ public class RandomDepthFirst {
         final Position end = this.maze.getEnd();
         final Tile endTile = this.maze.getEndTile();
 
-        if (end.getY() == 0) {
+        if (end.y() == 0) {
             endTile.enableDiggingToOrFrom(Direction.TOP);
             endTile.digFrom(Direction.TOP);
-        } else if (end.getX() == 0) {
+        } else if (end.x() == 0) {
             endTile.enableDiggingToOrFrom(Direction.LEFT);
             endTile.digFrom(Direction.LEFT);
-        } else if (end.getY() == this.maze.getHeight() - 1) {
+        } else if (end.y() == this.maze.getHeight() - 1) {
             endTile.enableDiggingToOrFrom(Direction.BOTTOM);
             endTile.digFrom(Direction.BOTTOM);
-        } else if (end.getX() == this.maze.getWidth() - 1) {
+        } else if (end.x() == this.maze.getWidth() - 1) {
             endTile.enableDiggingToOrFrom(Direction.RIGHT);
             endTile.digFrom(Direction.RIGHT);
         }
@@ -86,16 +87,16 @@ public class RandomDepthFirst {
         final Position start = this.maze.getStart();
         final Tile startTile = this.maze.getStartTile();
 
-        if (start.getY() == 0) {
+        if (start.y() == 0) {
             startTile.enableDiggingToOrFrom(Direction.TOP);
             startTile.digTo(Direction.TOP);
-        } else if (start.getX() == 0) {
+        } else if (start.x() == 0) {
             startTile.enableDiggingToOrFrom(Direction.LEFT);
             startTile.digTo(Direction.LEFT);
-        } else if (start.getY() == this.maze.getHeight() - 1) {
+        } else if (start.y() == this.maze.getHeight() - 1) {
             startTile.enableDiggingToOrFrom(Direction.BOTTOM);
             startTile.digTo(Direction.BOTTOM);
-        } else if (start.getX() == this.maze.getWidth() - 1) {
+        } else if (start.x() == this.maze.getWidth() - 1) {
             startTile.enableDiggingToOrFrom(Direction.RIGHT);
             startTile.digTo(Direction.RIGHT);
         }

src/main/java/ch/fritteli/maze/generator/model/Direction.java

@@ -7,17 +7,11 @@ public enum Direction {
     LEFT;
 
     public Direction invert() {
-        switch (this) {
+        return switch (this) {
-            case TOP:
+            case TOP -> BOTTOM;
-                return BOTTOM;
+            case RIGHT -> LEFT;
-            case RIGHT:
+            case BOTTOM -> TOP;
-                return LEFT;
+            case LEFT -> RIGHT;
-            case BOTTOM:
+        };
-                return TOP;
-            case LEFT:
-                return RIGHT;
-            default:
-                throw new IllegalStateException("Programming error: Not all enum values covered in enum Direction#invert()!");
-        }
     }
 }

src/main/java/ch/fritteli/maze/generator/model/Maze.java

@@ -3,8 +3,8 @@ package ch.fritteli.maze.generator.model;
 import io.vavr.control.Option;
 import lombok.EqualsAndHashCode;
 import lombok.Getter;
-import lombok.NonNull;
 import lombok.ToString;
+import org.jetbrains.annotations.NotNull;
 
 @EqualsAndHashCode
 @ToString
@@ -26,7 +26,7 @@ public class Maze {
         this(width, height, System.nanoTime());
     }
 
-    public Maze(final int width, final int height, @NonNull final Position start, @NonNull final Position end) {
+    public Maze(final int width, final int height, @NotNull final Position start, @NotNull final Position end) {
         this(width, height, System.nanoTime(), start, end);
     }
 
@@ -34,17 +34,17 @@ public class Maze {
         this(width, height, randomSeed, new Position(0, 0), new Position(width - 1, height - 1));
     }
 
-    public Maze(final int width, final int height, final long randomSeed, @NonNull final Position start, @NonNull final Position end) {
+    public Maze(final int width, final int height, final long randomSeed, @NotNull final Position start, @NotNull final Position end) {
         if (width <= 1 || height <= 1) {
             throw new IllegalArgumentException("width and height must be >1");
         }
         if (start.equals(end)) {
             throw new IllegalArgumentException("'start' must not be equal to 'end'");
         }
-        if (start.getX() != 0 && start.getX() != width - 1 && start.getY() != 0 && start.getY() != height - 1) {
+        if (start.x() != 0 && start.x() != width - 1 && start.y() != 0 && start.y() != height - 1) {
             throw new IllegalArgumentException("'start' must be at the edge of the maze");
         }
-        if (end.getX() != 0 && end.getX() != width - 1 && end.getY() != 0 && end.getY() != height - 1) {
+        if (end.x() != 0 && end.x() != width - 1 && end.y() != 0 && end.y() != height - 1) {
             throw new IllegalArgumentException("'end' must be at the edge of the maze");
         }
         this.width = width;
@@ -59,7 +59,7 @@ public class Maze {
     /**
      * INTERNAL API. Exists only for deserialization. Not to be called from user code.
      */
-    private Maze(@NonNull final Tile[][] field, final int width, final int height, final long randomSeed) {
+    private Maze(@NotNull final Tile[][] field, final int width, final int height, final long randomSeed) {
         this.field = field;
         this.width = width;
         this.height = height;
@@ -71,7 +71,7 @@ public class Maze {
     /**
      * INTERNAL API. Exists only for deserialization. Not to be called from user code.
      */
-    private Maze(@NonNull final Tile[][] field, final int width, final int height, @NonNull final Position start, @NonNull final Position end, final long randomSeed) {
+    private Maze(@NotNull final Tile[][] field, final int width, final int height, @NotNull final Position start, @NotNull final Position end, final long randomSeed) {
         this.field = field;
         this.width = width;
         this.height = height;
@@ -80,12 +80,12 @@ public class Maze {
         this.end = end;
     }
 
-    @NonNull
+    @NotNull
-    public Option<Tile> getTileAt(@NonNull final Position position) {
+    public Option<Tile> getTileAt(@NotNull final Position position) {
-        return this.getTileAt(position.getX(), position.getY());
+        return this.getTileAt(position.x(), position.y());
     }
 
-    @NonNull
+    @NotNull
     public Option<Tile> getTileAt(final int x, final int y) {
         if (x < 0 || y < 0 || x >= this.width || y >= this.height) {
             return Option.none();
@@ -93,12 +93,12 @@ public class Maze {
         return Option.of(this.field[x][y]);
     }
 
-    @NonNull
+    @NotNull
     public Tile getStartTile() {
         return this.getTileAt(this.start).get();
     }
 
-    @NonNull
+    @NotNull
     public Tile getEndTile() {
         return this.getTileAt(this.end).get();
     }
@@ -114,7 +114,7 @@ public class Maze {
         }
     }
 
-    private void hardenWalls(@NonNull final Tile tile, final int x, final int y) {
+    private void hardenWalls(@NotNull final Tile tile, final int x, final int y) {
         if (x == 0) {
             tile.preventDiggingToOrFrom(Direction.LEFT);
         }

src/main/java/ch/fritteli/maze/generator/model/Position.java

@@ -1,27 +1,16 @@
 package ch.fritteli.maze.generator.model;
 
-import lombok.NonNull;
-import lombok.Value;
 import lombok.With;
+import org.jetbrains.annotations.NotNull;
 
-@Value
 @With
-public class Position {
+public record Position(int x, int y) {
-    int x;
+    public Position move(@NotNull final Direction direction) {
-    int y;
+        return switch (direction) {
-
+            case BOTTOM -> this.withY(this.y + 1);
-    public Position move(@NonNull final Direction direction) {
+            case LEFT -> this.withX(this.x - 1);
-        switch (direction) {
+            case RIGHT -> this.withX(this.x + 1);
-            case BOTTOM:
+            case TOP -> this.withY(this.y - 1);
-                return this.withY(this.y + 1);
+        };
-            case LEFT:
-                return this.withX(this.x - 1);
-            case RIGHT:
-                return this.withX(this.x + 1);
-            case TOP:
-                return this.withY(this.y - 1);
-            default:
-                throw new IllegalStateException("Programming error: Not all Direction enum values covered in Position#move(Direction)!");
-        }
     }
 }

src/main/java/ch/fritteli/maze/generator/model/Tile.java

@@ -5,9 +5,9 @@ import io.vavr.control.Option;
 import lombok.AccessLevel;
 import lombok.EqualsAndHashCode;
 import lombok.Getter;
-import lombok.NonNull;
 import lombok.ToString;
 import lombok.experimental.FieldDefaults;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.EnumSet;
 import java.util.Random;
@@ -32,7 +32,7 @@ public class Tile {
      * @param walls
      * @param solution
      */
-    private Tile(@NonNull final EnumSet<Direction> walls, final boolean solution) {
+    private Tile(@NotNull final EnumSet<Direction> walls, final boolean solution) {
         for (final Direction direction : walls) {
             this.walls.set(direction);
             this.walls.harden(direction);
@@ -41,15 +41,15 @@ public class Tile {
         this.solution = solution;
     }
 
-    public void preventDiggingToOrFrom(@NonNull final Direction direction) {
+    public void preventDiggingToOrFrom(@NotNull final Direction direction) {
         this.walls.harden(direction);
     }
 
-    public void enableDiggingToOrFrom(@NonNull final Direction direction) {
+    public void enableDiggingToOrFrom(@NotNull final Direction direction) {
         this.walls.unharden(direction);
     }
 
-    public boolean digFrom(@NonNull final Direction direction) {
+    public boolean digFrom(@NotNull final Direction direction) {
         if (this.visited) {
             return false;
         }
@@ -57,15 +57,15 @@ public class Tile {
         return this.walls.clear(direction);
     }
 
-    public boolean digTo(@NonNull final Direction direction) {
+    public boolean digTo(@NotNull final Direction direction) {
         return this.walls.clear(direction);
     }
 
-    public void undigTo(@NonNull final Direction direction) {
+    public void undigTo(@NotNull final Direction direction) {
         this.walls.set(direction);
     }
 
-    public Option<Direction> getRandomAvailableDirection(@NonNull final Random random) {
+    public Option<Direction> getRandomAvailableDirection(@NotNull final Random random) {
         final Stream<Direction> availableDirections = this.walls.getUnhardenedSet();
         if (availableDirections.isEmpty()) {
             return Option.none();
@@ -74,7 +74,7 @@ public class Tile {
         return Option.of(availableDirections.get(index));
     }
 
-    public boolean hasWallAt(@NonNull final Direction direction) {
+    public boolean hasWallAt(@NotNull final Direction direction) {
         return this.walls.isSet(direction);
     }
 

src/main/java/ch/fritteli/maze/generator/model/Walls.java

@@ -2,8 +2,8 @@ package ch.fritteli.maze.generator.model;
 
 import io.vavr.collection.Stream;
 import lombok.EqualsAndHashCode;
-import lombok.NonNull;
 import lombok.ToString;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.EnumSet;
 import java.util.HashSet;
@@ -17,7 +17,7 @@ public class Walls {
     private final SortedSet<Direction> directions = new TreeSet<>();
     private final Set<Direction> hardened = new HashSet<>();
 
-    public void set(@NonNull final Direction direction) {
+    public void set(@NotNull final Direction direction) {
         this.directions.add(direction);
     }
 
@@ -25,14 +25,14 @@ public class Walls {
         this.directions.addAll(EnumSet.allOf(Direction.class));
     }
 
-    public boolean clear(@NonNull final Direction direction) {
+    public boolean clear(@NotNull final Direction direction) {
         if (this.hardened.contains(direction)) {
             return false;
         }
         return this.directions.remove(direction);
     }
 
-    public boolean isSet(@NonNull final Direction direction) {
+    public boolean isSet(@NotNull final Direction direction) {
         return this.directions.contains(direction);
     }
 
@@ -41,14 +41,14 @@ public class Walls {
                 .removeAll(this.hardened);
     }
 
-    public void harden(@NonNull final Direction direction) {
+    public void harden(@NotNull final Direction direction) {
         if (!this.directions.contains(direction)) {
             throw new IllegalStateException("Trying to harden cleared Direction: " + direction);
         }
         this.hardened.add(direction);
     }
 
-    public void unharden(@NonNull final Direction direction) {
+    public void unharden(@NotNull final Direction direction) {
         this.hardened.remove(direction);
     }
 }

src/main/java/ch/fritteli/maze/generator/renderer/Renderer.java

@@ -1,9 +1,9 @@
 package ch.fritteli.maze.generator.renderer;
 
 import ch.fritteli.maze.generator.model.Maze;
-import lombok.NonNull;
+import org.jetbrains.annotations.NotNull;
 
 public interface Renderer<T> {
-    @NonNull
+    @NotNull
-    T render(@NonNull final Maze maze);
+    T render(@NotNull final Maze maze);
 }

src/main/java/ch/fritteli/maze/generator/renderer/html/Generator.java

@@ -6,8 +6,8 @@ import ch.fritteli.maze.generator.model.Tile;
 import io.vavr.collection.HashSet;
 import io.vavr.collection.Set;
 import lombok.AccessLevel;
-import lombok.NonNull;
 import lombok.RequiredArgsConstructor;
+import org.jetbrains.annotations.NotNull;
 
 @RequiredArgsConstructor(access = AccessLevel.PACKAGE)
 class Generator {
@@ -31,7 +31,7 @@ class Generator {
         return sb.toString();
     }
 
-    private Set<String> getClasses(@NonNull final Tile tile) {
+    private Set<String> getClasses(@NotNull final Tile tile) {
         Set<String> result = HashSet.empty();
         if (tile.hasWallAt(Direction.TOP)) {
             result = result.add("top");

src/main/java/ch/fritteli/maze/generator/renderer/html/HTMLRenderer.java

@@ -2,7 +2,7 @@ package ch.fritteli.maze.generator.renderer.html;
 
 import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.renderer.Renderer;
-import lombok.NonNull;
+import org.jetbrains.annotations.NotNull;
 
 public class HTMLRenderer implements Renderer<String> {
 
@@ -112,14 +112,14 @@ public class HTMLRenderer implements Renderer<String> {
     private HTMLRenderer() {
     }
 
-    @NonNull
+    @NotNull
     public static HTMLRenderer newInstance() {
         return new HTMLRenderer();
     }
 
-    @NonNull
+    @NotNull
     @Override
-    public String render(@NonNull final Maze maze) {
+    public String render(@NotNull final Maze maze) {
         if (maze.getWidth() == 0 || maze.getHeight() == 0) {
             return this.getPreamble(maze) + POSTAMBLE;
         }
@@ -134,7 +134,7 @@ public class HTMLRenderer implements Renderer<String> {
         return sb.toString();
     }
 
-    private String getPreamble(@NonNull final Maze maze) {
+    private String getPreamble(@NotNull final Maze maze) {
         return "<!DOCTYPE html><html lang=\"en\">" +
                 "<head>" +
                 "<title>Maze " + maze.getWidth() + "x" + maze.getHeight() + ", ID " + maze.getRandomSeed() + "</title>" +

src/main/java/ch/fritteli/maze/generator/renderer/htmlfile/HTMLFileRenderer.java

@@ -5,8 +5,8 @@ import ch.fritteli.maze.generator.renderer.Renderer;
 import ch.fritteli.maze.generator.renderer.html.HTMLRenderer;
 import io.vavr.control.Option;
 import io.vavr.control.Try;
-import lombok.NonNull;
 import lombok.extern.slf4j.Slf4j;
+import org.jetbrains.annotations.NotNull;
 
 import java.io.File;
 import java.io.IOException;
@@ -17,9 +17,9 @@ import java.util.NoSuchElementException;
 
 @Slf4j
 public class HTMLFileRenderer implements Renderer<Path> {
-    @NonNull
+    @NotNull
     private static final HTMLRenderer HTML_RENDERER = HTMLRenderer.newInstance();
-    @NonNull
+    @NotNull
     private Option<Path> targetFile;
 
     private HTMLFileRenderer() {
@@ -29,7 +29,7 @@ public class HTMLFileRenderer implements Renderer<Path> {
                 .toOption();
     }
 
-    @NonNull
+    @NotNull
     public static HTMLFileRenderer newInstance() {
         return new HTMLFileRenderer();
     }
@@ -40,15 +40,15 @@ public class HTMLFileRenderer implements Renderer<Path> {
                 .exists(File::canWrite);
     }
 
-    @NonNull
+    @NotNull
-    public HTMLFileRenderer setTargetFile(@NonNull final Path targetFile) {
+    public HTMLFileRenderer setTargetFile(@NotNull final Path targetFile) {
         this.targetFile = Option.of(targetFile);
         return this;
     }
 
-    @NonNull
+    @NotNull
     @Override
-    public Path render(@NonNull final Maze maze) {
+    public Path render(@NotNull final Maze maze) {
         if (!this.isTargetFileDefinedAndWritable()) {
             try {
                 Files.createFile(this.targetFile.get());

src/main/java/ch/fritteli/maze/generator/renderer/json/Generator.java

@@ -7,8 +7,8 @@ import ch.fritteli.maze.generator.model.Direction;
 import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.model.Tile;
 import lombok.AccessLevel;
-import lombok.NonNull;
 import lombok.RequiredArgsConstructor;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -16,10 +16,10 @@ import java.util.List;
 @RequiredArgsConstructor(access = AccessLevel.PACKAGE)
 class Generator {
 
-    @NonNull
+    @NotNull
     private final Maze maze;
 
-    @NonNull
+    @NotNull
     JsonMaze generate() {
         final JsonMaze result = new JsonMaze();
         result.setId(String.valueOf(this.maze.getRandomSeed()));
@@ -30,7 +30,7 @@ class Generator {
             final ArrayList<JsonCell> row = new ArrayList<>();
             for (int x = 0; x < this.maze.getWidth(); x++) {
                 // x and y are not effectively final and can therefore not be accessed from within the lambda. Hence, create the string beforehand.
-                final String exceptionString = "Failed to obtain tile at %dx%d, although maze has dimensoins %dx%d"
+                final String exceptionString = "Failed to obtain tile at %dx%d, although maze has dimensions %dx%d"
                         .formatted(x, y, this.maze.getWidth(), this.maze.getHeight());
                 final Tile tile = this.maze.getTileAt(x, y)
                         .getOrElseThrow(() -> new IllegalStateException(exceptionString));
@@ -46,12 +46,12 @@ class Generator {
         }
         result.setGrid(rows);
         final JsonCoordinates start = new JsonCoordinates();
-        start.setX(this.maze.getStart().getX());
+        start.setX(this.maze.getStart().x());
-        start.setY(this.maze.getStart().getY());
+        start.setY(this.maze.getStart().y());
         result.setStart(start);
         final JsonCoordinates end = new JsonCoordinates();
-        end.setX(this.maze.getEnd().getX());
+        end.setX(this.maze.getEnd().x());
-        end.setY(this.maze.getEnd().getY());
+        end.setY(this.maze.getEnd().y());
         result.setEnd(end);
         return result;
     }

src/main/java/ch/fritteli/maze/generator/renderer/json/JsonRenderer.java

@@ -7,14 +7,14 @@ import ch.fritteli.maze.generator.renderer.Renderer;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.SerializationFeature;
-import lombok.NonNull;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.ArrayList;
 import java.util.List;
 
 public class JsonRenderer implements Renderer<String> {
 
-    @NonNull
+    @NotNull
     private final ObjectMapper objectMapper;
 
     private JsonRenderer() {
@@ -22,12 +22,12 @@ public class JsonRenderer implements Renderer<String> {
                 .enable(SerializationFeature.INDENT_OUTPUT);
     }
 
-    @NonNull
+    @NotNull
     public static JsonRenderer newInstance() {
         return new JsonRenderer();
     }
 
-    @NonNull
+    @NotNull
     private static JsonMaze createSingleCellMaze() {
         // This is the only cell.
         final JsonCell cell = new JsonCell();
@@ -37,7 +37,7 @@ public class JsonRenderer implements Renderer<String> {
         // Wrap that in a nested list.
         final List<List<JsonCell>> rows = new ArrayList<>();
         rows.add(new ArrayList<>());
-        rows.get(0).add(cell);
+        rows.getFirst().add(cell);
         // Wrap it all in an instance of JsonMaze.
         final JsonMaze jsonMaze = new JsonMaze();
         jsonMaze.setId("0");
@@ -45,8 +45,8 @@ public class JsonRenderer implements Renderer<String> {
         return jsonMaze;
     }
 
-    @NonNull
+    @NotNull
-    private String toString(@NonNull final JsonMaze jsonMaze) {
+    private String toString(@NotNull final JsonMaze jsonMaze) {
         try {
             return this.objectMapper.writeValueAsString(jsonMaze);
         } catch (final JsonProcessingException e) {
@@ -54,9 +54,9 @@ public class JsonRenderer implements Renderer<String> {
         }
     }
 
-    @NonNull
+    @NotNull
     @Override
-    public String render(@NonNull final Maze maze) {
+    public String render(@NotNull final Maze maze) {
         final JsonMaze jsonMaze;
         if (maze.getWidth() == 0 || maze.getHeight() == 0) {
             jsonMaze = createSingleCellMaze();

src/main/java/ch/fritteli/maze/generator/renderer/jsonfile/JsonFileRenderer.java

@@ -5,21 +5,22 @@ import ch.fritteli.maze.generator.renderer.Renderer;
 import ch.fritteli.maze.generator.renderer.json.JsonRenderer;
 import io.vavr.control.Option;
 import io.vavr.control.Try;
+import lombok.extern.slf4j.Slf4j;
+import org.jetbrains.annotations.NotNull;
+
 import java.io.File;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.NoSuchElementException;
-import lombok.NonNull;
-import lombok.extern.slf4j.Slf4j;
 
 @Slf4j
 public class JsonFileRenderer implements Renderer<Path> {
 
-    @NonNull
+    @NotNull
     private static final JsonRenderer JSON_RENDERER = JsonRenderer.newInstance();
-    @NonNull
+    @NotNull
     private Option<Path> targetFile;
 
     private JsonFileRenderer() {
@@ -29,7 +30,7 @@ public class JsonFileRenderer implements Renderer<Path> {
                 .toOption();
     }
 
-    @NonNull
+    @NotNull
     public static JsonFileRenderer newInstance() {
         return new JsonFileRenderer();
     }
@@ -40,15 +41,15 @@ public class JsonFileRenderer implements Renderer<Path> {
                 .exists(File::canWrite);
     }
 
-    @NonNull
+    @NotNull
-    public JsonFileRenderer setTargetFile(@NonNull final Path targetFile) {
+    public JsonFileRenderer setTargetFile(@NotNull final Path targetFile) {
         this.targetFile = Option.of(targetFile);
         return this;
     }
 
-    @NonNull
+    @NotNull
     @Override
-    public Path render(@NonNull final Maze maze) {
+    public Path render(@NotNull final Maze maze) {
         if (!this.isTargetFileDefinedAndWritable()) {
             try {
                 Files.createFile(this.targetFile.get());

src/main/java/ch/fritteli/maze/generator/renderer/pdf/Generator.java

@@ -5,11 +5,6 @@ import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.model.Position;
 import ch.fritteli.maze.generator.model.Tile;
 import io.vavr.control.Option;
-import java.awt.BasicStroke;
-import java.awt.Color;
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import lombok.NonNull;
 import lombok.RequiredArgsConstructor;
 import lombok.Value;
 import lombok.extern.slf4j.Slf4j;
@@ -18,16 +13,21 @@ import org.apache.pdfbox.pdmodel.PDDocumentInformation;
 import org.apache.pdfbox.pdmodel.PDPage;
 import org.apache.pdfbox.pdmodel.PDPageContentStream;
 import org.apache.pdfbox.pdmodel.common.PDRectangle;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.awt.*;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+
 @RequiredArgsConstructor
 @Slf4j
 class Generator {
 
-    @NonNull
+    @NotNull
     private final Maze maze;
 
-    @NonNull
+    @NotNull
     public ByteArrayOutputStream generate() {
         final float pageWidth = this.maze.getWidth() * PDFRenderer.SCALE + 2 * PDFRenderer.MARGIN;
         final float pageHeight = this.maze.getHeight() * PDFRenderer.SCALE + 2 * PDFRenderer.MARGIN;
@@ -60,7 +60,7 @@ class Generator {
         return output;
     }
 
-    private void setUpPageContentStream(@NonNull final PDPageContentStream pageContentStream) throws IOException {
+    private void setUpPageContentStream(@NotNull final PDPageContentStream pageContentStream) throws IOException {
         pageContentStream.setLineCapStyle(BasicStroke.CAP_ROUND);
         pageContentStream.setLineJoinStyle(BasicStroke.JOIN_ROUND);
         pageContentStream.setLineWidth(1.0f);
@@ -68,7 +68,7 @@ class Generator {
         pageContentStream.setNonStrokingColor(Color.BLACK);
     }
 
-    private void drawHorizontalLines(@NonNull final PDPageContentStream... contentStreams) throws IOException {
+    private void drawHorizontalLines(@NotNull final PDPageContentStream... contentStreams) throws IOException {
         // PDF has the origin in the lower left corner. We want it in the upper left corner, hence some magic is required.
         Coordinate coordinate = new Coordinate(0f, 0f);
         // Draw the TOP borders of all tiles.
@@ -136,7 +136,7 @@ class Generator {
         }
     }
 
-    private void drawVerticalLines(@NonNull final PDPageContentStream... contentStreams) throws IOException {
+    private void drawVerticalLines(@NotNull final PDPageContentStream... contentStreams) throws IOException {
         // PDF has the origin in the lower left corner. We want it in the upper left corner, hence some magic is required.
         Coordinate coordinate = new Coordinate(0f, 0f);
         // Draw the LEFT borders of all tiles.
@@ -204,27 +204,27 @@ class Generator {
         }
     }
 
-    private void drawSolution(@NonNull final PDPageContentStream pageContentStream) throws IOException {
+    private void drawSolution(@NotNull final PDPageContentStream pageContentStream) throws IOException {
         // Draw the solution in red
         pageContentStream.setStrokingColor(Color.RED);
         // PDF has the origin in the lower left corner. We want it in the upper left corner, hence some magic is required.
         final Position end = this.maze.getEnd();
         Position currentPosition = this.maze.getStart();
         Position previousPosition = null;
-        SolutionCoordinate coordinate = new SolutionCoordinate(currentPosition.getX(), currentPosition.getY());
+        SolutionCoordinate coordinate = new SolutionCoordinate(currentPosition.x(), currentPosition.y());
         pageContentStream.moveTo(coordinate.getX(), coordinate.getY());
         do {
             Position newCurrent = this.findNextSolutionPosition(previousPosition, currentPosition);
             previousPosition = currentPosition;
             currentPosition = newCurrent;
-            coordinate = new SolutionCoordinate(currentPosition.getX(), currentPosition.getY());
+            coordinate = new SolutionCoordinate(currentPosition.x(), currentPosition.y());
             pageContentStream.lineTo(coordinate.getX(), coordinate.getY());
         } while (!currentPosition.equals(end));
         pageContentStream.stroke();
     }
 
-    @NonNull
+    @NotNull
-    private Position findNextSolutionPosition(@Nullable final Position previousPosition, @NonNull final Position currentPosition) {
+    private Position findNextSolutionPosition(@Nullable final Position previousPosition, @NotNull final Position currentPosition) {
         final Tile currentTile = this.maze.getTileAt(currentPosition).get();
         for (final Direction direction : Direction.values()) {
             if (!currentTile.hasWallAt(direction)) {

src/main/java/ch/fritteli/maze/generator/renderer/pdf/PDFRenderer.java

@@ -2,9 +2,9 @@ package ch.fritteli.maze.generator.renderer.pdf;
 
 import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.renderer.Renderer;
-import java.io.ByteArrayOutputStream;
+import org.jetbrains.annotations.NotNull;
 
-import lombok.NonNull;
+import java.io.ByteArrayOutputStream;
 
 public class PDFRenderer implements Renderer<ByteArrayOutputStream> {
     static final float MARGIN = 10;
@@ -13,14 +13,14 @@ public class PDFRenderer implements Renderer<ByteArrayOutputStream> {
     private PDFRenderer() {
     }
 
-    @NonNull
+    @NotNull
     public static PDFRenderer newInstance() {
         return new PDFRenderer();
     }
 
-    @NonNull
+    @NotNull
     @Override
-    public ByteArrayOutputStream render(@NonNull final Maze maze) {
+    public ByteArrayOutputStream render(@NotNull final Maze maze) {
         final Generator generator = new Generator(maze);
         return generator.generate();
     }

src/main/java/ch/fritteli/maze/generator/renderer/pdffile/PDFFileRenderer.java

@@ -5,21 +5,22 @@ import ch.fritteli.maze.generator.renderer.Renderer;
 import ch.fritteli.maze.generator.renderer.pdf.PDFRenderer;
 import io.vavr.control.Option;
 import io.vavr.control.Try;
+import lombok.extern.slf4j.Slf4j;
+import org.jetbrains.annotations.NotNull;
+
 import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.NoSuchElementException;
-import lombok.NonNull;
-import lombok.extern.slf4j.Slf4j;
 
 @Slf4j
 public class PDFFileRenderer implements Renderer<Path> {
 
-    @NonNull
+    @NotNull
     private static final PDFRenderer PDF_RENDERER = PDFRenderer.newInstance();
-    @NonNull
+    @NotNull
     private Option<Path> targetFile;
 
     private PDFFileRenderer() {
@@ -29,7 +30,7 @@ public class PDFFileRenderer implements Renderer<Path> {
                 .toOption();
     }
 
-    @NonNull
+    @NotNull
     public static PDFFileRenderer newInstance() {
         return new PDFFileRenderer();
     }
@@ -40,15 +41,15 @@ public class PDFFileRenderer implements Renderer<Path> {
                 .exists(File::canWrite);
     }
 
-    @NonNull
+    @NotNull
-    public PDFFileRenderer setTargetFile(@NonNull final Path targetFile) {
+    public PDFFileRenderer setTargetFile(@NotNull final Path targetFile) {
         this.targetFile = Option.of(targetFile);
         return this;
     }
 
-    @NonNull
+    @NotNull
     @Override
-    public Path render(@NonNull final Maze maze) {
+    public Path render(@NotNull final Maze maze) {
         if (!this.isTargetFileDefinedAndWritable()) {
             try {
                 Files.createFile(this.targetFile.get());

src/main/java/ch/fritteli/maze/generator/renderer/text/Generator.java

@@ -5,12 +5,12 @@ import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.model.Tile;
 import io.vavr.control.Option;
 import lombok.AccessLevel;
-import lombok.NonNull;
 import lombok.RequiredArgsConstructor;
+import org.jetbrains.annotations.NotNull;
 
 @RequiredArgsConstructor(access = AccessLevel.PACKAGE)
 class Generator {
-    @NonNull
+    @NotNull
     private final Maze maze;
     private final boolean renderSolution;
     private int x = 0;
@@ -34,21 +34,12 @@ class Generator {
         final Option<Tile> rightTile = this.maze.getTileAt(this.x + 1, this.y);
         final Option<Tile> bottomTile = this.maze.getTileAt(this.x, this.y + 1);
         final Option<Tile> leftTile = this.maze.getTileAt(this.x - 1, this.y);
-        final String s;
+        final String s = switch (this.line) {
-        switch (this.line) {
+            case 0 -> this.renderTopLine(currentTile, leftTile, topTile);
-            case 0:
+            case 1 -> this.renderCenterLine(currentTile, topTile, rightTile, bottomTile, leftTile);
-                s = this.renderTopLine(currentTile, leftTile, topTile);
+            case 2 -> this.renderBottomLine(currentTile, leftTile);
-                break;
+            default -> "";
-            case 1:
+        };
-                s = this.renderCenterLine(currentTile, topTile, rightTile, bottomTile, leftTile);
-                break;
-            case 2:
-                s = this.renderBottomLine(currentTile, leftTile);
-                break;
-            default:
-                s = "";
-                break;
-        }
         this.prepareNextStep();
         return s;
     }
@@ -76,7 +67,7 @@ class Generator {
         }
     }
 
-    private String renderTopLine(@NonNull final Tile currentTile, @NonNull final Option<Tile> leftTile, @NonNull final Option<Tile> topTile) {
+    private String renderTopLine(@NotNull final Tile currentTile, @NotNull final Option<Tile> leftTile, @NotNull final Option<Tile> topTile) {
         final CharDefinition charDef1 = new CharDefinition();
         final CharDefinition charDef2 = new CharDefinition();
         final CharDefinition charDef3 = new CharDefinition();
@@ -112,11 +103,11 @@ class Generator {
         return result;
     }
 
-    private String renderCenterLine(@NonNull final Tile currentTile,
+    private String renderCenterLine(@NotNull final Tile currentTile,
-                                    @NonNull final Option<Tile> topTile,
+                                    @NotNull final Option<Tile> topTile,
-                                    @NonNull final Option<Tile> rightTile,
+                                    @NotNull final Option<Tile> rightTile,
-                                    @NonNull final Option<Tile> bottomTile,
+                                    @NotNull final Option<Tile> bottomTile,
-                                    @NonNull final Option<Tile> leftTile) {
+                                    @NotNull final Option<Tile> leftTile) {
         final CharDefinition charDef1 = new CharDefinition();
         final CharDefinition charDef2 = new CharDefinition();
         final CharDefinition charDef3 = new CharDefinition();
@@ -160,7 +151,7 @@ class Generator {
         return result;
     }
 
-    private String renderBottomLine(@NonNull final Tile currentTile, @NonNull final Option<Tile> leftTile) {
+    private String renderBottomLine(@NotNull final Tile currentTile, @NotNull final Option<Tile> leftTile) {
         String result;
         final CharDefinition charDef1 = new CharDefinition();
         final CharDefinition charDef2 = new CharDefinition();
@@ -193,15 +184,15 @@ class Generator {
         return result;
     }
 
-    private boolean hasWallAt(@NonNull final Option<Tile> tile, @NonNull final Direction direction) {
+    private boolean hasWallAt(@NotNull final Option<Tile> tile, @NotNull final Direction direction) {
         return tile.map(t -> t.hasWallAt(direction)).getOrElse(false);
     }
 
-    private boolean isSolution(@NonNull final Tile tile) {
+    private boolean isSolution(@NotNull final Tile tile) {
-        return this.renderSolution && tile != null && tile.isSolution();
+        return this.renderSolution && tile.isSolution();
     }
 
-    private boolean isSolution(@NonNull final Option<Tile> tile) {
+    private boolean isSolution(@NotNull final Option<Tile> tile) {
         return this.renderSolution && tile.map(Tile::isSolution).getOrElse(false);
     }
 }

src/main/java/ch/fritteli/maze/generator/renderer/text/TextRenderer.java

@@ -2,7 +2,7 @@ package ch.fritteli.maze.generator.renderer.text;
 
 import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.renderer.Renderer;
-import lombok.NonNull;
+import org.jetbrains.annotations.NotNull;
 
 public class TextRenderer implements Renderer<String> {
     private boolean renderSolution;
@@ -11,20 +11,20 @@ public class TextRenderer implements Renderer<String> {
         this.renderSolution = false;
     }
 
-    @NonNull
+    @NotNull
     public static TextRenderer newInstance() {
         return new TextRenderer();
     }
 
-    @NonNull
+    @NotNull
     public TextRenderer setRenderSolution(final boolean renderSolution) {
         this.renderSolution = renderSolution;
         return this;
     }
 
-    @NonNull
+    @NotNull
     @Override
-    public String render(@NonNull final Maze maze) {
+    public String render(@NotNull final Maze maze) {
         if (maze.getWidth() == 0 || maze.getHeight() == 0) {
             return "";
         }

src/main/java/ch/fritteli/maze/generator/renderer/textfile/TextFileRenderer.java

@@ -6,23 +6,22 @@ import ch.fritteli.maze.generator.renderer.text.TextRenderer;
 import io.vavr.collection.List;
 import io.vavr.control.Option;
 import io.vavr.control.Try;
-import lombok.NonNull;
 import lombok.extern.slf4j.Slf4j;
+import org.jetbrains.annotations.NotNull;
 
 import java.io.File;
 import java.io.IOException;
-import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.NoSuchElementException;
 
 @Slf4j
 public class TextFileRenderer implements Renderer<List<Path>> {
-    @NonNull
+    @NotNull
     private static final TextRenderer TEXT_RENDERER = TextRenderer.newInstance();
-    @NonNull
+    @NotNull
     private Option<Path> targetMazeFile;
-    @NonNull
+    @NotNull
     private Option<Path> targetSolutionFile;
 
     private TextFileRenderer() {
@@ -42,7 +41,7 @@ public class TextFileRenderer implements Renderer<List<Path>> {
                 .toOption();
     }
 
-    @NonNull
+    @NotNull
     public static TextFileRenderer newInstance() {
         return new TextFileRenderer();
     }
@@ -59,21 +58,21 @@ public class TextFileRenderer implements Renderer<List<Path>> {
                 .exists(File::canWrite);
     }
 
-    @NonNull
+    @NotNull
-    public TextFileRenderer setTargetMazeFile(@NonNull final Path targetMazeFile) {
+    public TextFileRenderer setTargetMazeFile(@NotNull final Path targetMazeFile) {
         this.targetMazeFile = Option.of(targetMazeFile);
         return this;
     }
 
-    @NonNull
+    @NotNull
-    public TextFileRenderer setTargetSolutionFile(@NonNull final Path targetSolutionFile) {
+    public TextFileRenderer setTargetSolutionFile(@NotNull final Path targetSolutionFile) {
         this.targetSolutionFile = Option.of(targetSolutionFile);
         return this;
     }
 
-    @NonNull
+    @NotNull
     @Override
-    public List<Path> render(@NonNull final Maze maze) {
+    public List<Path> render(@NotNull final Maze maze) {
         if (!this.isTargetMazeFileDefinedAndWritable()) {
             try {
                 Files.createFile(this.targetMazeFile.get());
@@ -98,12 +97,12 @@ public class TextFileRenderer implements Renderer<List<Path>> {
         final Path targetMazeFile = this.targetMazeFile.get();
         final Path targetSolutionFile = this.targetSolutionFile.get();
         try {
-            Files.write(targetMazeFile, text.getBytes(StandardCharsets.UTF_8));
+            Files.writeString(targetMazeFile, text);
         } catch (IOException e) {
             log.error("Failed writing to file " + targetMazeFile.normalize(), e);
         }
         try {
-            Files.write(targetSolutionFile, solution.getBytes(StandardCharsets.UTF_8));
+            Files.writeString(targetSolutionFile, solution);
         } catch (IOException e) {
             log.error("Failed writing to file " + targetSolutionFile.normalize());
         }

src/main/java/ch/fritteli/maze/generator/serialization/AbstractMazeInputStream.java

@@ -1,18 +1,19 @@
 package ch.fritteli.maze.generator.serialization;
 
 import ch.fritteli.maze.generator.model.Maze;
+import org.jetbrains.annotations.NotNull;
+
 import java.io.ByteArrayInputStream;
-import lombok.NonNull;
 
 public abstract class AbstractMazeInputStream extends ByteArrayInputStream {
 
-    public AbstractMazeInputStream(@NonNull final byte[] buf) {
+    public AbstractMazeInputStream(@NotNull final byte[] buf) {
         super(buf);
     }
 
     public abstract void checkHeader();
 
-    @NonNull
+    @NotNull
     public abstract Maze readMazeData();
 
     public byte readByte() {

src/main/java/ch/fritteli/maze/generator/serialization/AbstractMazeOutputStream.java

@@ -1,14 +1,15 @@
 package ch.fritteli.maze.generator.serialization;
 
 import ch.fritteli.maze.generator.model.Maze;
+import org.jetbrains.annotations.NotNull;
+
 import java.io.ByteArrayOutputStream;
-import lombok.NonNull;
 
 public abstract class AbstractMazeOutputStream extends ByteArrayOutputStream {
 
     public abstract void writeHeader();
 
-    public abstract void writeMazeData(@NonNull final Maze maze);
+    public abstract void writeMazeData(@NotNull final Maze maze);
 
     public void writeByte(final byte value) {
         this.write(value);

src/main/java/ch/fritteli/maze/generator/serialization/v1/MazeInputStreamV1.java

@@ -3,11 +3,11 @@ package ch.fritteli.maze.generator.serialization.v1;
 import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.model.Tile;
 import ch.fritteli.maze.generator.serialization.AbstractMazeInputStream;
-import lombok.NonNull;
+import org.jetbrains.annotations.NotNull;
 
 public class MazeInputStreamV1 extends AbstractMazeInputStream {
 
-    public MazeInputStreamV1(@NonNull final byte[] buf) {
+    public MazeInputStreamV1(@NotNull final byte[] buf) {
         super(buf);
     }
 
@@ -27,7 +27,7 @@ public class MazeInputStreamV1 extends AbstractMazeInputStream {
         }
     }
 
-    @NonNull
+    @NotNull
     @Override
     public Maze readMazeData() {
         final long randomSeed = this.readLong();

src/main/java/ch/fritteli/maze/generator/serialization/v1/MazeOutputStreamV1.java

@@ -3,7 +3,7 @@ package ch.fritteli.maze.generator.serialization.v1;
 import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.model.Tile;
 import ch.fritteli.maze.generator.serialization.AbstractMazeOutputStream;
-import lombok.NonNull;
+import org.jetbrains.annotations.NotNull;
 
 public class MazeOutputStreamV1 extends AbstractMazeOutputStream {
 
@@ -15,7 +15,7 @@ public class MazeOutputStreamV1 extends AbstractMazeOutputStream {
     }
 
     @Override
-    public void writeMazeData(@NonNull final Maze maze) {
+    public void writeMazeData(@NotNull final Maze maze) {
         final long randomSeed = maze.getRandomSeed();
         final int width = maze.getWidth();
         final int height = maze.getHeight();

src/main/java/ch/fritteli/maze/generator/serialization/v1/SerializerDeserializerV1.java

@@ -3,8 +3,8 @@ package ch.fritteli.maze.generator.serialization.v1;
 import ch.fritteli.maze.generator.model.Direction;
 import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.model.Tile;
-import lombok.NonNull;
 import lombok.experimental.UtilityClass;
+import org.jetbrains.annotations.NotNull;
 
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
@@ -62,8 +62,8 @@ public class SerializerDeserializerV1 {
      * @param maze The {@link Maze} to be serialized.
      * @return The resulting byte array.
      */
-    @NonNull
+    @NotNull
-    public byte[] serialize(@NonNull final Maze maze) {
+    public byte[] serialize(@NotNull final Maze maze) {
         final MazeOutputStreamV1 stream = new MazeOutputStreamV1();
         stream.writeHeader();
         stream.writeMazeData(maze);
@@ -76,38 +76,38 @@ public class SerializerDeserializerV1 {
      * @param bytes The byte array to be deserialized.
      * @return An instance of {@link Maze}.
      */
-    @NonNull
+    @NotNull
-    public Maze deserialize(@NonNull final byte[] bytes) {
+    public Maze deserialize(@NotNull final byte[] bytes) {
         final MazeInputStreamV1 stream = new MazeInputStreamV1(bytes);
         stream.checkHeader();
         return stream.readMazeData();
     }
 
-    @NonNull
+    @NotNull
-    Maze createMaze(@NonNull final Tile[][] field, final int width, final int height, final long randomSeed) {
+    Maze createMaze(@NotNull final Tile[][] field, final int width, final int height, final long randomSeed) {
         try {
             final Constructor<Maze> constructor = Maze.class.getDeclaredConstructor(Tile[][].class, Integer.TYPE, Integer.TYPE, Long.TYPE);
             constructor.setAccessible(true);
             return constructor.newInstance(field, width, height, randomSeed);
-        } catch (@NonNull final NoSuchMethodException | IllegalAccessException | InstantiationException |
+        } catch (@NotNull final NoSuchMethodException | IllegalAccessException | InstantiationException |
                                 InvocationTargetException e) {
             throw new RuntimeException("Can not deserialize Maze from maze data.", e);
         }
     }
 
-    @NonNull
+    @NotNull
-    private Tile createTile(@NonNull final EnumSet<Direction> walls, boolean solution) {
+    private Tile createTile(@NotNull final EnumSet<Direction> walls, boolean solution) {
         try {
             final Constructor<Tile> constructor = Tile.class.getDeclaredConstructor(EnumSet.class, Boolean.TYPE);
             constructor.setAccessible(true);
             return constructor.newInstance(walls, solution);
-        } catch (@NonNull final NoSuchMethodException | InstantiationException | IllegalAccessException |
+        } catch (@NotNull final NoSuchMethodException | InstantiationException | IllegalAccessException |
                                 InvocationTargetException e) {
             throw new RuntimeException("Can not deserialize Tile from maze data.", e);
         }
     }
 
-    byte getBitmaskForTile(@NonNull final Tile tile) {
+    byte getBitmaskForTile(@NotNull final Tile tile) {
         byte bitmask = 0;
         if (tile.hasWallAt(Direction.TOP)) {
             bitmask |= TOP_BIT;
@@ -127,7 +127,7 @@ public class SerializerDeserializerV1 {
         return bitmask;
     }
 
-    @NonNull
+    @NotNull
     Tile getTileForBitmask(final byte bitmask) {
         final EnumSet<Direction> walls = EnumSet.noneOf(Direction.class);
         if ((bitmask & TOP_BIT) == TOP_BIT) {

src/main/java/ch/fritteli/maze/generator/serialization/v2/MazeInputStreamV2.java

@@ -4,11 +4,11 @@ import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.model.Position;
 import ch.fritteli.maze.generator.model.Tile;
 import ch.fritteli.maze.generator.serialization.AbstractMazeInputStream;
-import lombok.NonNull;
+import org.jetbrains.annotations.NotNull;
 
 public class MazeInputStreamV2 extends AbstractMazeInputStream {
 
-    public MazeInputStreamV2(@NonNull final byte[] buf) {
+    public MazeInputStreamV2(@NotNull final byte[] buf) {
         super(buf);
     }
 
@@ -31,7 +31,7 @@ public class MazeInputStreamV2 extends AbstractMazeInputStream {
         }
     }
 
-    @NonNull
+    @NotNull
     @Override
     public Maze readMazeData() {
         // 03..06  width (int)

src/main/java/ch/fritteli/maze/generator/serialization/v2/MazeOutputStreamV2.java

@@ -4,7 +4,7 @@ import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.model.Position;
 import ch.fritteli.maze.generator.model.Tile;
 import ch.fritteli.maze.generator.serialization.AbstractMazeOutputStream;
-import lombok.NonNull;
+import org.jetbrains.annotations.NotNull;
 
 public class MazeOutputStreamV2 extends AbstractMazeOutputStream {
 
@@ -19,7 +19,7 @@ public class MazeOutputStreamV2 extends AbstractMazeOutputStream {
     }
 
     @Override
-    public void writeMazeData(@NonNull final Maze maze) {
+    public void writeMazeData(@NotNull final Maze maze) {
         // 03..06  width (int)
         // 07..10  height (int)
         // 11..14  start-x (int)
@@ -35,10 +35,10 @@ public class MazeOutputStreamV2 extends AbstractMazeOutputStream {
         final Position end = maze.getEnd();
         this.writeInt(width);
         this.writeInt(height);
-        this.writeInt(start.getX());
+        this.writeInt(start.x());
-        this.writeInt(start.getY());
+        this.writeInt(start.y());
-        this.writeInt(end.getX());
+        this.writeInt(end.x());
-        this.writeInt(end.getY());
+        this.writeInt(end.y());
         this.writeLong(randomSeed);
 
         for (int y = 0; y < height; y++) {

src/main/java/ch/fritteli/maze/generator/serialization/v2/SerializerDeserializerV2.java

@@ -4,8 +4,8 @@ import ch.fritteli.maze.generator.model.Direction;
 import ch.fritteli.maze.generator.model.Maze;
 import ch.fritteli.maze.generator.model.Position;
 import ch.fritteli.maze.generator.model.Tile;
-import lombok.NonNull;
 import lombok.experimental.UtilityClass;
+import org.jetbrains.annotations.NotNull;
 
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
@@ -67,8 +67,8 @@ public class SerializerDeserializerV2 {
      * @param maze The {@link Maze} to be serialized.
      * @return The resulting byte array.
      */
-    @NonNull
+    @NotNull
-    public byte[] serialize(@NonNull final Maze maze) {
+    public byte[] serialize(@NotNull final Maze maze) {
         final MazeOutputStreamV2 stream = new MazeOutputStreamV2();
         stream.writeHeader();
         stream.writeMazeData(maze);
@@ -81,38 +81,38 @@ public class SerializerDeserializerV2 {
      * @param bytes The byte array to be deserialized.
      * @return An instance of {@link Maze}.
      */
-    @NonNull
+    @NotNull
-    public Maze deserialize(@NonNull final byte[] bytes) {
+    public Maze deserialize(@NotNull final byte[] bytes) {
         final MazeInputStreamV2 stream = new MazeInputStreamV2(bytes);
         stream.checkHeader();
         return stream.readMazeData();
     }
 
-    @NonNull
+    @NotNull
-    Maze createMaze(@NonNull final Tile[][] field, final int width, final int height, @NonNull final Position start, @NonNull final Position end, final long randomSeed) {
+    Maze createMaze(@NotNull final Tile[][] field, final int width, final int height, @NotNull final Position start, @NotNull final Position end, final long randomSeed) {
         try {
             final Constructor<Maze> constructor = Maze.class.getDeclaredConstructor(Tile[][].class, Integer.TYPE, Integer.TYPE, Position.class, Position.class, Long.TYPE);
             constructor.setAccessible(true);
             return constructor.newInstance(field, width, height, start, end, randomSeed);
-        } catch (@NonNull final NoSuchMethodException | IllegalAccessException | InstantiationException |
+        } catch (@NotNull final NoSuchMethodException | IllegalAccessException | InstantiationException |
                                 InvocationTargetException e) {
             throw new RuntimeException("Can not deserialize Maze from maze data.", e);
         }
     }
 
-    @NonNull
+    @NotNull
-    private Tile createTile(@NonNull final EnumSet<Direction> walls, boolean solution) {
+    private Tile createTile(@NotNull final EnumSet<Direction> walls, boolean solution) {
         try {
             final Constructor<Tile> constructor = Tile.class.getDeclaredConstructor(EnumSet.class, Boolean.TYPE);
             constructor.setAccessible(true);
             return constructor.newInstance(walls, solution);
-        } catch (@NonNull final NoSuchMethodException | InstantiationException | IllegalAccessException |
+        } catch (@NotNull final NoSuchMethodException | InstantiationException | IllegalAccessException |
                                 InvocationTargetException e) {
             throw new RuntimeException("Can not deserialize Tile from maze data.", e);
         }
     }
 
-    byte getBitmaskForTile(@NonNull final Tile tile) {
+    byte getBitmaskForTile(@NotNull final Tile tile) {
         byte bitmask = 0;
         if (tile.hasWallAt(Direction.TOP)) {
             bitmask |= TOP_BIT;
@@ -132,7 +132,7 @@ public class SerializerDeserializerV2 {
         return bitmask;
     }
 
-    @NonNull
+    @NotNull
     Tile getTileForBitmask(final byte bitmask) {
         final EnumSet<Direction> walls = EnumSet.noneOf(Direction.class);
         if ((bitmask & TOP_BIT) == TOP_BIT) {

src/test/java/ch/fritteli/maze/generator/model/DirectionTest.java

@@ -1,13 +1,12 @@
 package ch.fritteli.maze.generator.model;
 
-import ch.fritteli.maze.generator.model.Direction;
 import org.junit.jupiter.api.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 class DirectionTest {
     @Test
-    void invert() {
+    void shouldInvertTheDirection() {
         assertThat(Direction.TOP.invert()).isEqualTo(Direction.BOTTOM);
         assertThat(Direction.RIGHT.invert()).isEqualTo(Direction.LEFT);
         assertThat(Direction.BOTTOM.invert()).isEqualTo(Direction.TOP);

src/test/java/ch/fritteli/maze/generator/model/MazeTest.java

@@ -7,14 +7,24 @@ import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 
 class MazeTest {
     @Test
-    void testConstruct() {
+    void shouldNotAccept0AsWidthOrHeight() {
-        // act / assert on simple cases
+        // act / assert
         assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> new Maze(0, 0))
                 .withMessage("width and height must be >1");
         assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> new Maze(0, 0, 0))
                 .withMessage("width and height must be >1");
+        assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> new Maze(0, 5))
+                .withMessage("width and height must be >1");
+        assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> new Maze(0, 5, 0))
+                .withMessage("width and height must be >1");
+        assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> new Maze(5, 0))
+                .withMessage("width and height must be >1");
+        assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> new Maze(5, 0, 0))
+                .withMessage("width and height must be >1");
+    }
 
-        // now for the real work:
+    @Test
+    void testConstruct() {
         // arrange
         final Maze sut = new Maze(2, 3, 5);
 
@@ -23,7 +33,9 @@ class MazeTest {
                 .returns(2, Maze::getWidth)
                 .returns(3, Maze::getHeight)
                 .returns(5L, Maze::getRandomSeed)
-                .returns(new Position(0, 0), Maze::getStart)
+                .satisfies(
-                .returns(new Position(1, 2), Maze::getEnd);
+                        maze -> assertThat(maze.getStart()).isEqualTo(new Position(0, 0)),
+                        maze -> assertThat(maze.getEnd()).isEqualTo(new Position(1, 2))
+                );
     }
 }

src/test/java/ch/fritteli/maze/generator/model/PositionTest.java

@@ -1,14 +1,12 @@
 package ch.fritteli.maze.generator.model;
 
-import ch.fritteli.maze.generator.model.Direction;
-import ch.fritteli.maze.generator.model.Position;
 import org.junit.jupiter.api.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 class PositionTest {
     @Test
-    void move() {
+    void shouldMoveToCorrectNeighborPosition() {
         // arrange
         final Position sut = new Position(0, 0);
 

src/test/java/ch/fritteli/maze/generator/model/TileTest.java

@@ -1,7 +1,5 @@
 package ch.fritteli.maze.generator.model;
 
-import ch.fritteli.maze.generator.model.Direction;
-import ch.fritteli.maze.generator.model.Tile;
 import io.vavr.control.Option;
 import org.junit.jupiter.api.Test;
 
@@ -11,21 +9,20 @@ import static org.assertj.core.api.Assertions.assertThat;
 
 class TileTest {
     @Test
-    void testConstruct() {
+    void shouldConstructATileWithDefaultValues() {
         // arrange / act
         final Tile sut = new Tile();
 
         //assert
-        assertThat(sut)
+        assertThat(sut.hasWallAt(Direction.TOP)).isTrue();
-                .returns(true, v -> v.hasWallAt(Direction.TOP))
+        assertThat(sut.hasWallAt(Direction.RIGHT)).isTrue();
-                .returns(true, v -> v.hasWallAt(Direction.RIGHT))
+        assertThat(sut.hasWallAt(Direction.BOTTOM)).isTrue();
-                .returns(true, v -> v.hasWallAt(Direction.BOTTOM))
+        assertThat(sut.hasWallAt(Direction.LEFT)).isTrue();
-                .returns(true, v -> v.hasWallAt(Direction.LEFT))
+        assertThat(sut.isSolution()).isFalse();
-                .returns(false, Tile::isSolution);
     }
 
     @Test
-    void testDigFrom() {
+    void tileCanBeDugIntoOnlyOnce() {
         // arrange
         final Tile sut = new Tile();
 
@@ -45,29 +42,27 @@ class TileTest {
     }
 
     @Test
-    void testDigTo() {
+    void canDigToDirectionOnlyOnce() {
         // arrange
         final Tile sut = new Tile();
 
         // act / assert
-        assertThat(sut)
+        assertThat(sut.digTo(Direction.TOP)).isTrue();
-                .returns(true, v -> v.digTo(Direction.TOP))
+        assertThat(sut.digTo(Direction.RIGHT)).isTrue();
-                .returns(true, v -> v.digTo(Direction.RIGHT))
+        assertThat(sut.digTo(Direction.BOTTOM)).isTrue();
-                .returns(true, v -> v.digTo(Direction.BOTTOM))
+        assertThat(sut.digTo(Direction.LEFT)).isTrue();
-                .returns(true, v -> v.digTo(Direction.LEFT))
         // digging a second time does not succeed
-                .returns(false, v -> v.digTo(Direction.LEFT));
+        assertThat(sut.digTo(Direction.LEFT)).isFalse();
 
         // assert
-        assertThat(sut)
+        assertThat(sut.hasWallAt(Direction.TOP)).isFalse();
-                .returns(false, v -> v.hasWallAt(Direction.TOP))
+        assertThat(sut.hasWallAt(Direction.RIGHT)).isFalse();
-                .returns(false, v -> v.hasWallAt(Direction.RIGHT))
+        assertThat(sut.hasWallAt(Direction.BOTTOM)).isFalse();
-                .returns(false, v -> v.hasWallAt(Direction.BOTTOM))
+        assertThat(sut.hasWallAt(Direction.LEFT)).isFalse();
-                .returns(false, v -> v.hasWallAt(Direction.LEFT));
     }
 
     @Test
-    void testPreventDiggingToOrFrom() {
+    void canNotDigToOrFromDirectionWhenPrevented() {
         // arrange
         final Tile sut = new Tile();
 
@@ -75,10 +70,11 @@ class TileTest {
         sut.preventDiggingToOrFrom(Direction.LEFT);
 
         // assert
-        assertThat(sut)
+        assertThat(sut.digTo(Direction.LEFT)).isFalse();
-                .returns(false, v -> v.digTo(Direction.LEFT))
+        assertThat(sut.digFrom(Direction.LEFT)).isFalse();
-                .returns(false, v -> v.digFrom(Direction.LEFT))
+        assertThat(sut.hasWallAt(Direction.LEFT)).isTrue();
-                .returns(true, v -> v.hasWallAt(Direction.LEFT));
+        // Digging in another direction is still permitted
+        assertThat(sut.digTo(Direction.RIGHT)).isTrue();
     }
 
     @Test