@Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        //定位textView1 根据ID找到控件

        TextView tv1 = (TextView) this.findViewById(R.id.textView1);

        //对控件进行赋值，改变内容

        tv1.setText("你好，android一班");

    }

 package com.example.helloword;

 import android.app.Activity;

 import android.os.Bundle;

 import android.view.Menu;

 import android.view.MenuItem;

 import android.widget.TextView;

 public class MainActivity extends Activity {

     @Override

     protected void onCreate(Bundle savedInstanceState) {

         super.onCreate(savedInstanceState);

         setContentView(R.layout.activity_main);

         TextView tv1 = (TextView) this.findViewById(R.id.textView1);

         tv1.setText("你好，Android 1班");

     }

     @Override

     public boolean onCreateOptionsMenu(Menu menu) {

         getMenuInflater().inflate(R.menu.main, menu);

         return true;

     }

     @Override

     public boolean onOptionsItemSelected(MenuItem item) {

         int id = item.getItemId();

         if (id == R.id.action_settings) {

             return true;

         }

         return super.onOptionsItemSelected(item);

     }

 }