Android activity reopen after start a new activity -

i have activity called mainactivity calls new activity (tutorial):

intent secondactivity = new intent(this, tutorial.class); startactivity(secondactivity); 

after calling startactivity, oncreate of mainactivity open again. why happens? migrated eclipse android studio, , issue did not happen on eclipse.

@update1:

the mainactivity first activity open on project. after call tutorialactivity.

manifest.xml:

<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.teste.animationxml" > <uses-permission android:name="android.permission.internet" /> <uses-permission android:name="android.permission.access_network_state"/> <uses-permission android:name="android.permission.access_wifi_state"/>   <application     android:allowbackup="true"     android:icon="@mipmap/ic_launcher"     android:label="@string/app_name"     android:largeheap="true"     android:theme="@style/apptheme">      <activity         android:name=".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=".tutorial">     </activity>      <activity     android:name=".volume"     android:label="app_second" >     </activity>      <activity         android:name=".parabens"         android:label="app_second" >     </activity>  </application> 

regards

best regards