Show arrow back button in Activity Toolbar (Android)

show_back_button_toolbar_android.txt

PS.: It will not work on MainActivity.

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
      ...
      
      // insert this two lines
      getSupportActionBar().setDisplayHomeAsUpEnabled(true);
      getSupportActionBar().setHomeButtonEnabled(true);
    }
    
    // override this method
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if(item.getItemId() == android.R.id.home) {
            finish();
        }
        return super.onOptionsItemSelected(item);
    }