Android several common return key overwrite mode

// 第一种
public boolean onKeyDown(int keyCode, KeyEvent event) {

// press the back button on the keyboard 
IF (keyCode == KeyEvent.KEYCODE_BACK) { 

    new new AlertDialog.Builder (the this) 
            .setMessage ( "OK to exit the system do?") 
            .SetNegativeButton ( "Cancel", 
                    new new DialogInterface.OnClickListener () { 
                        void the onClick public (DialogInterface Dialog, 
                                            int Which) { 
                        } 
                    }) 
            .setPositiveButton ( "OK", 
                    new new DialogInterface.OnClickListener () { 
                        public void the onClick (DialogInterface Dialog, 
                                            int whichButton) { 
                            Finish ();
                        }
                    }).show();

    return true;
} else {
    return super.onKeyDown(keyCode, event);
}

}

// Exit the program directly
@Override
protected void onDestroy () {
　　super.onDestroy ();
　　// this manner or following
　　//System.exit(0);
　　// this suggested
　　android.os.Process.killProcess (android .os.Process.myPid ());
}

 

// 第二种
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
　　if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
　　　　return true;
　　}
　　return super.onKeyDown(keyCode, event);
}

 

// third
@Override
public void onBackPressed () {
　　super.onBackPressed ();
}