【ANDROID STUDIO】 Runtime Menu

package com.example.runtimemenu;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    private final int MENU_DOWNLOAD = 1;
    private final int MENU_SETTINGS = 2;
    private boolean showDownloadMenu = false;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    public void toggleMenu(View view) {
        showDownloadMenu = !showDownloadMenu;
        invalidateOptionsMenu();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        menu.add(0, MENU_DOWNLOAD, 0, R.string.menu_download);
        menu.add(0, MENU_SETTINGS, 0, R.string.menu_settings);
        return true;
    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        MenuItem menuItem = menu.findItem(MENU_DOWNLOAD);
        menuItem.setVisible(showDownloadMenu);
        menuItem.setShowAsAction(MenuItem.SHOW_AS_ACTION_ALWAYS);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case MENU_DOWNLOAD:
                Toast.makeText(this, R.string.menu_download, Toast.LENGTH_LONG).show();
                break;
            case MENU_SETTINGS:
                Toast.makeText(this, R.string.menu_settings, Toast.LENGTH_LONG).show();
                break;
            default:
                return super.onContextItemSelected(item);
        }
        return true;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button android:id="@+id/buttonToggleMenu"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Toggle Menu"
        android:onClick="toggleMenu"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>