How to use Application class in android

ApplicationClassAndroid

//*****************************************SET these things in Activity*******************************************************//
public class MainActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		AppController appState = ((AppController)getApplicationContext());

		//Set the value in application variable
		AppController.setMyState("helloWorld");
		
	    String state = AppController.getMyState();
	    Log.d("LOGCAT", state);
	}
}

//***********************************SET THESE THINGS in a class that extends application*************************************//
package com.example.createapplicationvariable;

import android.app.Application;

public class AppController extends Application{

	private static String myState;


	public static String getMyState() {
		return myState;
	}

	public static void setMyState(String _myState) {
		myState =_myState;
	}
}


//**************************************Manifest Declaration (mention the application class presence)*********************//

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.createapplicationvariable"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="14" />

    <application
        android:name="com.example.createapplicationvariable.AppController"
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>