android通过代码的形式来实现应用程序的方法

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="安装"
        android:onClick="install"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="卸载"
        android:onClick="uninstall"
        />
</LinearLayout>

package com.njupt.install;
import java.io.File;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
public class MainActivity extends Activity {
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
 }
 public void install(View v){
  Intent intent = new Intent();
  intent.setAction(Intent.ACTION_VIEW);
  File file = new File(Environment.getExternalStorageDirectory(),"HtmlUI1.apk");
  intent.setDataAndType(Uri.fromFile(file), "application/vnd.android.package-archive");
  startActivity(intent);
 }
 public void uninstall(View v){
  Intent intent = new Intent();
     intent.setAction(Intent.ACTION_DELETE);
     intent.setData(Uri.parse("package:com.njupt.htmlui1"));
  startActivity(intent);
 }
 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater().inflate(R.menu.main, menu);
  return true;
 }
}