title: Every activity can use "android.intent.action.MAIN"?
body: <p>aid with this example at <a href="https://stackoverflow.com/questions/14848590/return-back-to-mainactivity-from-another-activity">Return back to MainActivity from another activity</a>
  I copy that codes as follow,</p>
  
  <pre><code>&lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
   &lt;uses-sdk
      android:minSdkVersion="10"
      android:targetSdkVersion="15" /&gt;
  
  &lt;application
  android:icon="@drawable/ic_launcher"
  android:label="@string/app_name"
  android:theme="@style/AppTheme" &gt;
  &lt;activity
      android:name=".MainActivity"
      android:label="@string/title_activity_main" &gt;
      &lt;intent-filter&gt;
          &lt;action android:name="android.intent.action.MAIN" /&gt;
  
          &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
      &lt;/intent-filter&gt;
  &lt;/activity&gt;
  &lt;activity
      android:name=".Activity1"
      android:label="@string/title_activity_main" &gt;
      &lt;intent-filter&gt;
          &lt;action android:name="android.intent.action.ACTIVITY001" /&gt;
  
          &lt;category android:name="android.intent.category.DEFAULT" /&gt;
      &lt;/intent-filter&gt;
  &lt;/activity&gt;
  &lt;activity
      android:name=".Activity2"
      android:label="@string/title_activity_main" &gt;
      &lt;intent-filter&gt;
          &lt;action android:name="android.intent.action.ACTIVITY002" /&gt;
  
          &lt;category android:name="android.intent.category.DEFAULT" /&gt;
      &lt;/intent-filter&gt;
  &lt;/activity&gt;
  &lt;activity
      android:name=".Activity3"
      android:label="@string/title_activity_main" &gt;
      &lt;intent-filter&gt;
          &lt;action android:name="android.intent.action.ACTIVITY003" /&gt;
  
          &lt;category android:name="android.intent.category.DEFAULT" /&gt;
      &lt;/intent-filter&gt;
  &lt;/activity&gt;
  &lt;/application&gt;
  </code></pre>
  
  <p>So many statements: action android:name="android.intent.action.MAIN"; if I would use their class path to instead of them, they can also do the job. what's different from these two ways?</p>