Android - Back button in the title bar

Question

In many apps (Calendar, Drive, Play Store) when you tap a button and enter a new activity, the icon in the title bar turns into a back button, but for the app I am making, i

Answer 1

After a quality time I have found, theme option is the main problem in my code And following is the proper way to show the toolbar for me

In AndroidManifest file first you have to change your theme style

Theme.AppCompat.Light.DarkActionBar
to 
Theme.AppCompat.Light.NoActionBar

then at your activity xml you need to call your own Toolbar like

And then this toolbar should be called in your Java file by

Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

And for toolbar showing U should check the null to avoid NullPointerException

if(getSupportActionBar() != null){
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}

For Home activity back add this

@Override
public boolean onOptionsItemSelected(MenuItem item) {
        if (item.getItemId()==android.R.id.home) {
            finish();
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

OR for your desired activity back

public boolean onOptionsItemSelected(MenuItem item){
    Intent myIntent = new Intent(getApplicationContext(), YourActivity.class);
    startActivityForResult(myIntent, 0);
    return true;
}