added strategy pattern sample

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();
+	}
+}