I made Tab Bar using Fragment on Android, but there was an error, so I'm asking you this question.

public class MainActivity extends AppCompatActivity {
    Toolbar toolbar;
    Fragment fragment1;
    Fragment fragment2;
    Fragment fragment3;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

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

        ActionBar actionBar = getSupportActionBar();
        actionBar.setDisplayShowTitleEnabled(false);

        //...
    }
}