close the application while a button is clicked in android

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http://stackoverflow.com – I want to close the application and force close when i click this button. Here is the code that I've tried so far. But the application doesn't close. How can I make the app close when the button is pushed? import java.io.IOException; import android.app.Activity; import android.content.DialogInterface; import android.content.res.AssetFileDescriptor; import android.media.MediaPlayer; import android.os.Bundle; import android.util.Log; import android.view.View; import android.widget.Button; public class MainActivity extends Activity implements setOnCompletionListener{ (HowTos)