android 加一个旋钮，退出程序

 package com.example.yanlei.yl;import android.graphics.Color;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;import android.widget.TextView;import android.text.Html;import android.text.Html.ImageGetter;import java.util.regex.Matcher;import java.util.regex.Pattern;import android.text.Editable;import android.text.TextWatcher;import android.widget.EditText;import android.widget.Button;import android.app.Activity;import android.app.AlertDialog;import android.app.AlertDialog.Builder;import android.content.DialogInterface;import android.content.DialogInterface.OnClickListener;import android.app.Activity;import android.content.Intent;import android.net.Uri;import android.os.Bundle;import android.view.Menu;import android.view.View;import android.widget.Button;import android.widget.EditText;protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        View btn1 = this.findViewById(R.id.button1);        btn1.setOnClickListener(new ButtonClickListener());    }    private class ButtonClickListener implements View.OnClickListener {        public void onClick(View v) {            //System.exit(0);            android.os.Process.killProcess(android.os.Process.myPid());        }    }

 <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="退出程序"        android:id="@+id/button1"        android:layout_marginTop="157dp"        android:layout_alignParentTop="true"        android:layout_alignParentLeft="true"        android:layout_alignParentStart="true"        android:layout_marginLeft="96dp"        android:layout_marginStart="96dp" />