Added state pattern sample

state/src/main/java/com/iluwatar/AngryState.java

@@ -0,0 +1,21 @@
+package com.iluwatar;
+
+public class AngryState implements State {
+
+	private Mammoth mammoth;
+
+	public AngryState(Mammoth mammoth) {
+		this.mammoth = mammoth;
+	}
+	
+	@Override
+	public void observe() {
+		System.out.println(String.format("%s is furious!", mammoth));
+	}
+
+	@Override
+	public void onEnterState() {
+		System.out.println(String.format("%s gets angry!", mammoth));
+	}
+
+}

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

@@ -0,0 +1,16 @@
+package com.iluwatar;
+
+public class App 
+{
+    public static void main( String[] args )
+    {
+
+    	Mammoth mammoth = new Mammoth();
+    	mammoth.observe();
+    	mammoth.timePasses();
+    	mammoth.observe();
+    	mammoth.timePasses();
+    	mammoth.observe();
+    	
+    }
+}

state/src/main/java/com/iluwatar/Mammoth.java

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+package com.iluwatar;
+
+public class Mammoth {
+	
+	private State state;
+
+	public Mammoth() {
+		state = new PeacefulState(this);
+	}
+	
+	public void timePasses() {
+		if (state.getClass().equals(PeacefulState.class)) {
+			changeStateTo(new AngryState(this));
+		} else {
+			changeStateTo(new PeacefulState(this));
+		}
+	}
+
+	private void changeStateTo(State newState) {
+		this.state = newState;
+		this.state.onEnterState();
+	}
+	
+	@Override
+	public String toString() {
+		return "The mammoth";
+	}
+	
+	public void observe() {
+		this.state.observe();
+	}
+}

state/src/main/java/com/iluwatar/PeacefulState.java

@@ -0,0 +1,21 @@
+package com.iluwatar;
+
+public class PeacefulState implements State {
+	
+	private Mammoth mammoth;
+
+	public PeacefulState(Mammoth mammoth) {
+		this.mammoth = mammoth;
+	}
+
+	@Override
+	public void observe() {
+		System.out.println(String.format("%s is calm and peaceful.", mammoth));
+	}
+
+	@Override
+	public void onEnterState() {
+		System.out.println(String.format("%s calms down.", mammoth));
+	}
+	
+}

state/src/main/java/com/iluwatar/State.java

@@ -0,0 +1,9 @@
+package com.iluwatar;
+
+public interface State {
+
+	void onEnterState();
+	
+	void observe();
+	
+}