请问下这个关机代码哪里错了
package yu.bin;import android.app.Activity;import android.content.Intent;import android.net.Uri;import android.os.Bundle;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;public class poweroff extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button t = (Button) findViewById(R.id.abc); t.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub Intent shutdown = new Intent(Intent.ACTION_SHUTDOWN); startActivity(shutdown); } }); }}<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" package="yu.bin" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".poweroff" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:sharedUserId="android.uid.system" android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion="8" /> <uses-permission android:name="android.intent.action.ACTION_SHUTDOWN" /></manifest>