Toolbar

Toolbar is act like actionbar and have more extra features.It can be supported below v 21 also if you use AppCompat V7 lib

public class MainActivity extends AppCompatActivity {

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);

setSupportActionBar(myToolbar);

}

public void hideToolbar(View v){

// startActivity(new Intent(this,ChildActivity.class));

ActionBar actionBar = getSupportActionBar();

if(actionBar.isShowing()){

actionBar.hide();

}else {

actionBar.show();

}

}

}

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

<RelativeLayout android:layout_width="match_parent"

android:layout_height="match_parent"

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

xmlns:app="http://schemas.android.com/apk/res-auto">

<android.support.v7.widget.Toolbar

android:id="@+id/my_toolbar"

android:layout_width="match_parent"

android:layout_height="?attr/actionBarSize"

android:background="?attr/colorPrimary"

android:elevation="4dp"

android:theme="@style/ThemeOverlay.AppCompat.ActionBar"

app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>

<Button

android:layout_below="@+id/my_toolbar"

android:onClick="hideToolbar"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="click me"/>

</RelativeLayout>