<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.example.chenshuai.test">

    <application

        android:allowBackup="true"

        android:icon="@mipmap/ic_launcher"

        android:label="@string/app_name"

        android:supportsRtl="true"

        android:theme="@style/AppTheme">

        <!--谁在前启动谁-->

        <activity android:name=".Axtivity2">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

        <activity android:name=".MainActivity">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

    </application>

</manifest>

<?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:weightSum="1">

    <!--匹配父窗口  match_parent

        包裹内容    wrap_content-->

    <TextClock

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

       android:text="大家好"

      />

</LinearLayout>

package com.hanqi.text3;

import android.app.Activity;

import android.os.Bundle;

//继承了Activity

public class MainActivity extends Activity {

    @Override //覆盖  重写了父类的onCreate()

    protected void onCreate(Bundle savedInstanceState) {

        //super  父类

        //调用了父类的方法

        super.onCreate(savedInstanceState);

        //设置Java代码和layout文件的关联

        //通过R文件的id值

        setContentView(R.layout.activity_main);

    }

}

package com.example.chenshuai.test;

import android.app.Activity;

import android.os.Bundle;

import android.util.Log;

/**

 * Created by chenshuai on 2016/3/16.

 */

public class Axtivity2 extends Activity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.layoutactivity);

        System.out.println("这是我运行的第一个Activity");

        //输出日志

        Log.d("test","Log输出的信息");

        Log.w("test","Log输出的信息");//warning 蓝色

        Log.e("test","Log输出的信息");//eror 红色

        Log.i("test","Log输出的信息");

        Log.v("test","Log输出的信息");

    }

}