Add lightweight example with test

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/flyweight/GameWorld.java

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+package pl.mperor.lab.java.design.pattern.structural.flyweight;
+
+import pl.mperor.lab.java.design.pattern.structural.flyweight.terrain.Terrain;
+
+import java.util.Arrays;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.stream.Collectors;
+
+public class GameWorld {
+
+    private final int width;
+    private final int height;
+    private final Terrain[][] tiles;
+
+    public GameWorld(int width, int height) {
+        assert width >= 0;
+        assert height >= 0;
+
+        this.width = width;
+        this.height = height;
+        this.tiles = generateTiles();
+    }
+
+    private Terrain[][] generateTiles() {
+        Terrain[][] tiles = new Terrain[width][height];
+        ThreadLocalRandom random = ThreadLocalRandom.current();
+        Terrain[] terrains = Terrain.values();
+
+        for (int x = 0; x < tiles.length; x++) {
+            for (int y = 0; y < tiles[0].length; y++) {
+                tiles[x][y] = terrains[random.nextInt(terrains.length)];
+            }
+        }
+
+        return tiles;
+    }
+
+    public Terrain getTiles(int x, int y) {
+        assert x >= 0 && x < tiles.length ;
+        assert y >= 0 && y < tiles[0].length;
+
+        return tiles[x][y];
+    }
+
+    @Override
+    public String toString() {
+        return Arrays.stream(tiles)
+                .map(Arrays::toString)
+                .collect(Collectors.joining(System.lineSeparator()));
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/flyweight/terrain/GrassTexture.java

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+package pl.mperor.lab.java.design.pattern.structural.flyweight.terrain;
+
+public record GrassTexture() implements TerrainTexture {
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/flyweight/terrain/SandTexture.java

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+package pl.mperor.lab.java.design.pattern.structural.flyweight.terrain;
+
+public record SandTexture() implements TerrainTexture {
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/flyweight/terrain/Terrain.java

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+package pl.mperor.lab.java.design.pattern.structural.flyweight.terrain;
+
+public enum Terrain {
+
+    WATER("W", new WaterTexture(), 1),
+    SAND("S", new SandTexture(), 2),
+    GRASS("G", new GrassTexture(), 3);
+
+    private final String name;
+    private final TerrainTexture terrainTexture;
+    private final int movementCost;
+
+    Terrain(String name, TerrainTexture terrainTexture, int movementCost) {
+        this.name = name;
+        this.terrainTexture = terrainTexture;
+        this.movementCost = movementCost;
+    }
+
+    public TerrainTexture getTerrainTexture() {
+        return terrainTexture;
+    }
+
+    public int getMovementCost() {
+        return movementCost;
+    }
+
+    @Override
+    public String toString() {
+        return name;
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/flyweight/terrain/TerrainTexture.java

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+package pl.mperor.lab.java.design.pattern.structural.flyweight.terrain;
+
+public sealed interface TerrainTexture permits GrassTexture, SandTexture, WaterTexture {
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/flyweight/terrain/WaterTexture.java

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+package pl.mperor.lab.java.design.pattern.structural.flyweight.terrain;
+
+public record WaterTexture() implements TerrainTexture {
+}

DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/structural/flyweight/GameWorldTest.java

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+package pl.mperor.lab.java.design.pattern.structural.flyweight;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import pl.mperor.lab.java.design.pattern.structural.flyweight.terrain.Terrain;
+
+import java.util.Arrays;
+
+
+public class GameWorldTest {
+
+    @Test
+    public void testCreatedGameWorldContainsOnlyTerrainTilesWithTheSameTexture() {
+        GameWorld gw = new GameWorld(20, 20);
+        System.out.println(gw);
+        Terrain firstTile = gw.getTiles(0, 0);
+
+        Assertions.assertTrue(Arrays.stream(Terrain.values())
+                        .map(Terrain::getTerrainTexture)
+                        .anyMatch(texture -> texture == firstTile.getTerrainTexture()),
+                "The same instance is used for the terrain texture!");
+    }
+
+}