Android close all below Activities

AndroidManifest

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.app" >

    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:theme="@style/AppBaseTheme"
        android:name=".MyApp">

        <activity
            android:name="com.example.app.activities.FirstActivity"
            android:label="@string/title_activity_first"
            android:taskAffinity="@string/task_affinity_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.example.app.activities.SecondActivity"
            android:label="@string/title_activity_second"
            android:taskAffinity="@string/task_affinity_name">
        </activity>
        <activity
            android:name="com.example.app.activities.ThirdActivity"
            android:label="@string/title_activity_third"
            android:taskAffinity="@string/task_affinity_name">
        </activity>
    </application>

</manifest>

CommonActivity

public class CommonActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        MyApp.mBackStackActivities.put(getComponentName().getClassName(), this);
    }

    @Override
    protected void onDestroy(){
        MyApp.mBackStackActivities.remove(getComponentName().getClassName());
        super.onDestroy();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.common, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        switch (id){
            case android.R.id.home:
                finish();
                break;
            case R.id.action_first: {
                Intent intent = new Intent(this,FirstActivity.class);
                startActivity(intent);
            }
            break;
            case R.id.action_second: {
                Intent intent = new Intent(this,SecondActivity.class);
                startActivity(intent);
            }
            break;
            case R.id.action_third: {
                Intent intent = new Intent(this,ThirdActivity.class);
                startActivity(intent);
            }
            break;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void startActivity(Intent intent) {

        if(MyApp.mBackStackActivities
            .containsKey(intent.getComponent().getClassName())){
            if(android.os.Build.VERSION.SDK_INT >= 16) {
                Activity activity = MyApp.mBackStackActivities.get(intent.getComponent().getClassName());
                // finish the activity as well as all the below Activities.
                activity.finishAffinity(); // supported from API 16
            }else {
                // loop through all the below activity and finish it
            }
        }
        super.startActivity(intent);
    }

}

MyApp

public class MyApp extends Application {
    public static HashMap<String , CommonActivity > mBackStackActivities
        = new HashMap<String, CommonActivity>();

}