patterns11FlyweightPattern

1package pkg8patterns;2 3/*4 * Flyweight (Structural)5 * ----------------------6 * INTENT: share fine-grained objects to support large numbers efficiently by7 *         separating intrinsic (shared) state from extrinsic (context) state.8 * UML: FlyweightFactory caches Flyweights; client passes extrinsic state per call.9 * PROS: huge memory savings when many objects share state.10 * CONS: complexity; must split state carefully.11 * REAL-WORLD: Integer.valueOf cache (-128..127), String pool, glyph rendering.12 */13import java.util.*;14 15public class patterns11FlyweightPattern {16 17    // Intrinsic (shared) state: the tree species18    static class TreeType {19        final String name, color;20        TreeType(String name, String color) { this.name = name; this.color = color; }21        String draw(int x, int y) { return name + "(" + color + ") at (" + x + "," + y + ")"; }22    }23 24    // Factory ensures one TreeType object per unique species25    static class TreeFactory {26        private final Map<String, TreeType> cache = new HashMap<>();27        TreeType get(String name, String color) {28            return cache.computeIfAbsent(name + "-" + color, k -> new TreeType(name, color));29        }30        int distinctTypes() { return cache.size(); }31    }32 33    public static void main(String[] args) {34        TreeFactory factory = new TreeFactory();35        // Plant 1000 trees but only a few shared TreeType objects exist36        List<String> forest = new ArrayList<>();37        for (int i = 0; i < 1000; i++) {38            TreeType type = factory.get(i % 2 == 0 ? "Oak" : "Pine", i % 2 == 0 ? "green" : "dark-green");39            forest.add(type.draw(i, i));   // extrinsic state (x,y) passed in40        }41        System.out.println("planted " + forest.size() + " trees");42        System.out.println("distinct shared TreeType objects = " + factory.distinctTypes());43        System.out.println("sample: " + forest.get(0));44    }45}