How to create button in Action bar in android [duplicate]

In your activity class, override the following methods if they are not there by default:

// create an action bar button
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // R.menu.mymenu is a reference to an xml file named mymenu.xml which should be inside your res/menu directory. 
    // If you don't have res/menu, just create a directory named "menu" inside res
    getMenuInflater().inflate(R.menu.mymenu, menu);
    return super.onCreateOptionsMenu(menu);
}

// handle button activities
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();

    if (id == R.id.mybutton) {
    // do something here
    }
    return super.onOptionsItemSelected(item);
}

mymenu.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto">
<item
    android:id="@+id/mybutton"
    android:title=""
    app:showAsAction="always"
    android:icon="@drawable/mybuttonicon"
    />
</menu>