Added state pattern sample

pom.xml

@@ -37,6 +37,7 @@
     <module>mediator</module>
     <module>memento</module>
     <module>observer</module>
+    <module>state</module>
   </modules>
   
 <build>

state/pom.xml

@@ -0,0 +1,23 @@
+<?xml version="1.0"?>
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.0-SNAPSHOT</version>
+  </parent>
+  <groupId>com.iluwatar</groupId>
+  <artifactId>state</artifactId>
+  <version>1.0-SNAPSHOT</version>
+  <name>state</name>
+  <url>http://maven.apache.org</url>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>3.8.1</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

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

@@ -0,0 +1,32 @@
+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();
+	
+}