example_menu.xmlMainActivity.java
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <item
        android:id="@+id/item1"
        android:icon="@drawable/ic_icon"
        android:title="Item 1"
        app:showAsAction="ifRoom" />

    <item
        android:id="@+id/item2"
        android:title="Item 2"
        app:showAsAction="never" />

    <item
        android:id="@+id/item3"
        android:title="Item 3"
        app:showAsAction="never">

        <menu>

            <item
                android:id="@+id/subitem1"
                android:title="Sub Item 1" />

            <item
                android:id="@+id/subitem2"
                android:title="Sub Item 2" />

        </menu>

    </item>

</menu>
package com.example.application.optionsmenuexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.example_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.item1:
                Toast.makeText(this, "Item 1 selected", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.item2:
                Toast.makeText(this, "Item 2 selected", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.item3:
                Toast.makeText(this, "Item 3 selected", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.subitem1:
                Toast.makeText(this, "Sub Item 1 selected", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.subitem2:
                Toast.makeText(this, "Sub Item 2 selected", Toast.LENGTH_SHORT).show();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }
}