android : what's the procedure to write functions for alertdialog item?

I'm going to write s开发者_StackOverflow中文版ome function in AlertDialog's item : - Code is : -

final CharSequence[] items = {"Now", "Later", "Cancel"};

        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("When you need to Take BackUp?");
        builder.setSingleChoiceItems(items, -1, new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int item) 
            {
        //                  Toast.makeText(getApplicationContext(),items[item],Toast.LENGTH_SHORT).show();
                items[0].notify();
                items[1].charAt(2);
            }
        });
        builder.show();

This item will enable some function, how can i declare and define that.

The item that is selected will be passed into the onClick method, the int item in the method's signature.

public void onClick(DialogInterface dialog, int item) {
    switch(item) {
        case 0: // the first item in the CharSequence[]
            callUserClickedNow();
            break;
        case 1: // the second item in the CharSequence[]
            callUserClickedLater();
            break;
        case 2: // the thirditem in the CharSequence[]
            callUserClickedCancel();
            break;
    }
    dialog.dismiss();
}

Then outside of the method where you create the AlertDialog:

private void callUserClickedNow() {
    // do stuff
}

etc...