简单android代码

package com.example.yt;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity {
    private Button btn;
    private Button ban;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn=(Button)findViewById(R.id.button1);
        btn.setOnClickListener(new OnClickListener(){
         @Override
         public void onClick(View agr0){
          System.out.println("helloworld");
          Intent in=new Intent(MainActivity.this,Sec.class);
          startActivity(in);
          }});
      
    }

    @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;
    }
   
}----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------package com.example.yt;

import java.util.ArrayList;
import java.util.List;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;

public class Wheatera extends Activity {
    private ListView username;
    private Button btn3;
    List list;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_weathera);
  btn3=(Button)findViewById(R.id.button5);
  btn3.setOnClickListener(new OnClickListener(){
   @Override
        public void onClick(View agr0){
     Intent on3=new Intent(Wheatera.this,Three.class);
  startActivity(on3);
  }});
  
  username=(ListView)findViewById(R.id.usernameview);
  list=new ArrayList();
  list.add("yt");
  list.add("xiaohei");
  list.add("doudou");
  list.add("huitailang");
  ArrayAdapter<String> adapter=new
    ArrayAdapter<String>
  (this,android.R.layout.simple_expandable_list_item_1,list);
  username.setAdapter(adapter);
  
 }
 

 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater().inflate(R.menu.sec, menu);
  return true;
 }

}
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------package com.example.yt;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.MenuItem;

public class Three extends Activity {
 
    final static int menu_first=Menu.FIRST;
    final static int menu_sec=Menu.FIRST+1;
    final static int menu_three=Menu.FIRST+2;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_three);
 }

 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
  // Inflate the menu; this adds items to the action bar if it is present.
  //getMenuInflater().inflate(R.menu.three, menu);
  menu.add(0, menu_first, 0, "首页").setIcon(android.R.drawable.arrow_down_float);
  
  menu.add(0, menu_sec, 0, "内容").setIcon(android.R.drawable.btn_star_big_on);
  menu.add(0, menu_three, 0, "尾页").setIcon(android.R.drawable.alert_dark_frame);
  
    
  
  return true;
 }

 @Override
 public boolean onOptionsItemSelected(MenuItem item) {
  // TODO Auto-generated method stub
  //return super.onOptionsItemSelected(item);
  switch (item.getItemId()){
      case menu_first:
   System.out.println("menu001");
   System.out.println(android.R.drawable.alert_dark_frame);
   return true;
   case menu_sec:
   System.out.println("menu002");
   return true;
   case menu_three:
    System.out.println("menu_three");
   }return false;
  
 }

}