Android AlertDialog

package com.example.myact4;

import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
/**
 * AlertDialog练习
 * @author shaobn
 *
 */
public class MainActivity extends ActionBarActivity {
private Button button;
private TextView tView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button) this.findViewById(R.id.button1);
        tView = (TextView) this.findViewById(R.id.textView1);
        final Handler handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                // TODO Auto-generated method stub
                super.handleMessage(msg);
                int num = msg.arg1;
                MainActivity.this.tView.setText(String.valueOf(num));
                Toast.makeText(MainActivity.this, Thread.currentThread().getName(), Toast.LENGTH_LONG).show();
            }
        };
        button.setOnClickListener(new OnClickListener() {
            
            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
            AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
            builder.setIcon(R.drawable.ic_launcher);
            builder.setTitle("友情提示");
            builder.setMessage("您确定要删除吗？");
            builder.setNegativeButton("取消", new DialogInterface.OnClickListener() {
                
                @Override
                public void onClick(DialogInterface arg0, int arg1) {
                    // TODO Auto-generated method stub
                    arg0.cancel();
                }
            });
            builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {
                
                @Override
                public void onClick(DialogInterface arg0, int arg1) {
                    // TODO Auto-generated method stub
                    Runnable runnable=new Runnable() {
                            
                            @Override
                            public void run() {
                                // TODO Auto-generated method stub
                                Message message = new Message();
                                message.arg1 = 3;
                                handler.sendMessage(message);
                                
                            }
                        };
                    new Thread(runnable).start();
                }
            });
            AlertDialog alertDialog = builder.create();
            alertDialog.show();
            }
        });
    
    
    }    
}