android - How can I program the back button on the action bar to go back to the previous activity? -

i want know how can program button in action bar revert previous activity , finish activity shown?

about.class

public class extends fragmentactivity {     @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.about);         getactionbar().setdisplayhomeasupenabled(true); // tracker.         tracker t = ((analyticstracker) getapplication()).gettracker(analyticstracker.trackername.app_tracker);  // enable display features can see demographics in google analytics         t.enableadvertisingidcollection(true);  // set screen name.         t.setscreenname("about");  // send screen view.         t.send(new hitbuilders.appviewbuilder().build());         fragmentmanager fragmentmanager = getfragmentmanager();         android.app.fragmenttransaction fragmenttransaction =                 fragmentmanager.begintransaction();          adview ls_fragment = new adview();         fragmenttransaction.replace(android.r.id.content, ls_fragment);          adview madview = (adview) findviewbyid(r.id.adview);         adrequest adrequest = new adrequest.builder().build();         madview.loadad(adrequest);      }  } 

the layout page. about.xml

<?xml version="1.0" encoding="utf-8"?>     <relativelayout         xmlns:android="http://schemas.android.com/apk/res/android"         xmlns:ads="http://schemas.android.com/apk/res-auto"         xmlns:tools="http://schemas.android.com/tools"         android:id = "@+id/content_frame"         android:layout_width="match_parent"         android:layout_height="match_parent"         android:background="@color/black"         >       <relativelayout             android:background="@mipmap/home"             android:layout_width="match_parent"             android:layout_height="match_parent">              <imageview                 android:layout_width="200dp"                 android:layout_height="200dp"                 android:id="@+id/imageview"                 android:background="@mipmap/ic_launcher"                 android:layout_alignparenttop="true"                 android:layout_centerhorizontal="true" />          <textview             android:layout_width="300dp"             android:layout_height="250dp"             android:id="@+id/textview9"             android:gravity="center"             android:textsize="16dp"             android:text="@string/abouttext"             android:background="@drawable/text"             android:layout_below="@+id/imageview"             android:layout_centerhorizontal="true" />          <fragment             android:layout_width="match_parent"             android:layout_height="50dp"             android:name="course.labs.converjz.adview"             android:id="@+id/fragment"             tools:layout="@layout/adview"             android:layout_gravity="center|bottom"             android:layout_alignwithparentifmissing="false"             android:layout_alignparentbottom="true"             android:layout_alignparentstart="true" />      </relativelayout> </relativelayout> 

the specific style creates actionbar , adds button it. styles.xml

 <style name= "menubar" parent="@style/appbasetheme">         <item name = "android:homeasupindicator">@mipmap/back</item>  </style> 

the button image in mipmap icon folder.

just change getactionbar getsupportactionbar shown:

getsupportactionbar().setdisplayhomeasupenabled(true);