LinearLayout layout=new LinearLayout(this);
setContentView(layout);

setContentView(R.layout.main);

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
  xmlns:tools="http://schemas.android.com/tools" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" 
  android:paddingBottom="@dimen/activity_vertical_margin" 
  android:paddingLeft="@dimen/activity_horizontal_margin" 
  android:paddingRight="@dimen/activity_horizontal_margin" 
  android:paddingTop="@dimen/activity_vertical_margin" 
  tools:context=".MainActivity" > 
  <Button  
    android:id="@+id/button1" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:text="启动一个Activity"/> 
 
</RelativeLayout> 

<?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" > 
   
  <TextView  
    android:id="@+id/textview1" 
    android:layout_height="wrap_content" 
    android:layout_width="match_parent" 
    android:text="第二个activity" 
    android:gravity="center_horizontal"/> 
   
</LinearLayout> 

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
  package="com.android.xiong.moreactivity" 
  android:versionCode="1" 
  android:versionName="1.0" > 
 
  <uses-sdk 
    android:minSdkVersion="8" 
    android:targetSdkVersion="17" /> 
 
  <application 
    android:allowBackup="true" 
    android:icon="@drawable/ic_launcher" 
    android:label="@string/app_name" 
    android:theme="@style/AppTheme" > 
    <activity 
      android:name="com.android.xiong.moreactivity.MainActivity" 
      android:label="@string/app_name" > 
      <intent-filter> 
        <action android:name="android.intent.action.MAIN" /> 
 
        <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
    </activity> 
    <activity android:name="com.android.xiong.moreactivity.SecondActivity" 
      android:label="secondActivity"> 
    </activity> 
  </application> 
 
</manifest> 

package com.android.xiong.moreactivity; 
 
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 button1; 
 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    button1=(Button)findViewById(R.id.button1); 
    OnClick onc=new OnClick(); 
    button1.setOnClickListener(onc); 
  } 
   
   
  class OnClick implements OnClickListener{ 
     
    /** 
     * setClass的第一个方法的参数是一个Context 一个参数是表示你要启动那个Activity 是一个class对象 
     * Context是activity的父类 
     */ 
    @Override 
    public void onClick(View v) { 
      // TODO Auto-generated method stub 
      Intent intent=new Intent(); 
      intent.setClass(MainActivity.this, SecondActivity.class); 
      MainActivity.this.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; 
  } 


}