added strategy pattern sample

strategy/src/main/java/com/iluwatar/App.java

@@ -0,0 +1,17 @@
+package com.iluwatar;
+
+public class App 
+{
+    public static void main( String[] args )
+    {
+    	System.out.println("Green dragon spotted ahead!");
+    	DragonSlayer dragonSlayer = new DragonSlayer(new MeleeStrategy());
+    	dragonSlayer.goToBattle();
+    	System.out.println("Red dragon emerges.");
+    	dragonSlayer.changeStrategy(new ProjectileStrategy());
+    	dragonSlayer.goToBattle();
+    	System.out.println("Black dragon lands before you.");
+    	dragonSlayer.changeStrategy(new SpellStrategy());
+    	dragonSlayer.goToBattle();
+    }
+}

strategy/src/main/java/com/iluwatar/DragonSlayer.java

@@ -0,0 +1,18 @@
+package com.iluwatar;
+
+public class DragonSlayer {
+
+	private DragonSlayingStrategy strategy;
+
+	public DragonSlayer(DragonSlayingStrategy strategy) {
+		this.strategy = strategy;
+	}
+
+	public void changeStrategy(DragonSlayingStrategy strategy) {
+		this.strategy = strategy;
+	}
+	
+	public void goToBattle() {
+		strategy.execute();
+	}
+}

strategy/src/main/java/com/iluwatar/DragonSlayingStrategy.java

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+package com.iluwatar;
+
+public interface DragonSlayingStrategy {
+
+	void execute();
+	
+}

strategy/src/main/java/com/iluwatar/MeleeStrategy.java

@@ -0,0 +1,10 @@
+package com.iluwatar;
+
+public class MeleeStrategy implements DragonSlayingStrategy {
+
+	@Override
+	public void execute() {
+		System.out.println("With your Excalibur you severe the dragon's head!");
+	}
+
+}

strategy/src/main/java/com/iluwatar/ProjectileStrategy.java

@@ -0,0 +1,10 @@
+package com.iluwatar;
+
+public class ProjectileStrategy implements DragonSlayingStrategy {
+
+	@Override
+	public void execute() {
+		System.out.println("You shoot the dragon with the magical crossbow and it falls dead on the ground!");
+	}
+
+}

strategy/src/main/java/com/iluwatar/SpellStrategy.java

@@ -0,0 +1,10 @@
+package com.iluwatar;
+
+public class SpellStrategy implements DragonSlayingStrategy {
+
+	@Override
+	public void execute() {
+		System.out.println("You cast the spell of disintegration and the dragon vaporizes in a pile of dust!");
+	}
+
+}