added strategy example

src/learn/simple_strategy/Context.java

@@ -0,0 +1,17 @@
+package learn.simple_strategy;
+
+public class Context {
+    private Strategy currentStrategy;
+
+    public Context(Strategy currentStrategy) {
+        this.currentStrategy = currentStrategy;
+    }
+
+    public void setCurrentStrategy(Strategy currentStrategy) {
+        this.currentStrategy = currentStrategy;
+    }
+
+    public void doSomeJob() {
+        currentStrategy.algorithm();
+    }
+}