Check out example codes for "android java remove action bar". It will help you in understanding the concepts better.

Code Example 1

// In your Styles.xml file, change:
parent="Theme.AppCompat.Light.DarkActionBar" 

// to:
parent="Theme.AppCompat.Light.NoActionBar"

Code Example 2

ActionBar actionBar=getSupportActionBar();
    actionBar.hide();

Learn ReactJs, React Native from akashmittal.com