added flyweight example

src/learn/simple_flyweight/ConcreteFlyweight.java

@@ -0,0 +1,15 @@
+package learn.simple_flyweight;
+
+public class ConcreteFlyweight extends Flyweight {
+    private long intrinsicState;
+
+    public ConcreteFlyweight(long intrinsicState) {
+        super();
+        this.intrinsicState = intrinsicState;
+    }
+
+    @Override
+    public void operation(long extrinsicState) {
+        System.out.println("Flyweight " + intrinsicState + " calling operation with extrinsic state " + extrinsicState);
+    }
+}

src/learn/simple_flyweight/Flyweight.java

@@ -0,0 +1,13 @@
+package learn.simple_flyweight;
+
+import java.util.Arrays;
+
+public abstract class Flyweight {
+    private long[] internalStorage = new long[1000000];
+
+    public Flyweight() {
+        Arrays.fill(internalStorage, 1);
+    }
+
+    public abstract void operation(long extrinsicState);
+}

src/learn/simple_flyweight/FlyweightFactory.java

@@ -0,0 +1,17 @@
+package learn.simple_flyweight;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class FlyweightFactory {
+    private static final Map<Integer, Flyweight> flyweights = new HashMap<>();
+
+    public Flyweight getFlyweight(Integer key) {
+        Flyweight flyweight = flyweights.get(key);
+        if (flyweight == null) {
+            flyweight = new ConcreteFlyweight(key);
+            flyweights.put(key, flyweight);
+        }
+        return flyweight;
+    }
+}

src/learn/simple_flyweight/Main.java

@@ -0,0 +1,40 @@
+package learn.simple_flyweight;
+
+import java.util.Random;
+
+public class Main {
+    private static final Random rand = new Random();
+
+    public static void main(String[] args) {
+        int rounds = 100;
+
+        debugMemory();
+        testFlyweight(rounds);
+        debugMemory();
+        testUnsharedFlyweight(rounds);
+        debugMemory();
+    }
+
+    private static void debugMemory() {
+        long totalMemory = Runtime.getRuntime().totalMemory();
+        long freeMemory = Runtime.getRuntime().freeMemory();
+        long usedMemory = totalMemory - freeMemory;
+        System.out.printf("Memory: %d%n", usedMemory);
+    }
+
+    private static void testFlyweight(int rounds) {
+        FlyweightFactory factory = new FlyweightFactory();
+
+        for (int i = 0; i < rounds; i++) {
+            Flyweight flyweight = factory.getFlyweight(rand.nextInt(10));
+            flyweight.operation(i);
+        }
+    }
+
+    private static void testUnsharedFlyweight(int rounds) {
+        for (int i = 0; i < rounds; i++) {
+            Flyweight flyweight = new UnsharedConcreteFlyweight(rand.nextInt(10));
+            flyweight.operation(i);
+        }
+    }
+}

src/learn/simple_flyweight/UnsharedConcreteFlyweight.java

@@ -0,0 +1,15 @@
+package learn.simple_flyweight;
+
+public class UnsharedConcreteFlyweight extends Flyweight {
+    private long allState;
+
+    public UnsharedConcreteFlyweight(long allState) {
+        super();
+        this.allState = allState;
+    }
+
+    @Override
+    public void operation(long extrinsicState) {
+        System.out.println("Unshared Flyweight " + allState + " calling operation with extrinsic state " + extrinsicState);
+    }
+}