Android toolbar menu is not showing

I was also facing the same problem, but the actual error was, i forgot to introduce toolbar in java activity

under AppCompactActivity, under on create method define your toolbar by id and call setSupportActionBar(ToolBar);

Example is below:

public class secondActivity extends AppCompatActivity {
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);

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