android 实现点击手机的MENU键，弹出选项菜单，其中菜单项有：科目、爱好。点击科目弹出Java语言、Python语言、Android。点击爱好菜单项则弹出子菜单，分别为运动、学习、看书和爬山。点击每一个子菜单项，用toast提示菜单项的内容。

首先，在MainActivity.java中实现以下代码：

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) {
        getMenuInflater().inflate(R.menu.main_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.subject_menu:
                showSubjectMenu();
                return true;
            case R.id.hobby_menu:
                showHobbyMenu();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

    // 显示科目菜单
    private void showSubjectMenu() {
        PopupMenu popupMenu = new PopupMenu(this, findViewById(R.id.subject_menu));
        popupMenu.getMenuInflater().inflate(R.menu.subject_menu, popupMenu.getMenu());
        popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
            @Override
            public boolean onMenuItemClick(MenuItem item) {
                switch (item.getItemId()) {
                    case R.id.java_subject:
                        Toast.makeText(MainActivity.this, "Java语言", Toast.LENGTH_SHORT).show();
                        return true;
                    case R.id.python_subject:
                        Toast.makeText(MainActivity.this, "Python语言", Toast.LENGTH_SHORT).show();
                        return true;
                    case R.id.android_subject:
                        Toast.makeText(MainActivity.this, "Android", Toast.LENGTH_SHORT).show();
                        return true;
                    default:
                        return false;
                }
            }
        });
        popupMenu.show();
    }

    // 显示爱好菜单
    private void showHobbyMenu() {
        PopupMenu popupMenu = new PopupMenu(this, findViewById(R.id.hobby_menu));
        popupMenu.getMenuInflater().inflate(R.menu.hobby_menu, popupMenu.getMenu());
        popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
            @Override
            public boolean onMenuItemClick(MenuItem item) {
                switch (item.getItemId()) {
                    case R.id.sports_hobby:
                        Toast.makeText(MainActivity.this, "运动", Toast.LENGTH_SHORT).show();
                        return true;
                    case R.id.study_hobby:
                        Toast.makeText(MainActivity.this, "学习", Toast.LENGTH_SHORT).show();
                        return true;
                    case R.id.read_hobby:
                        Toast.makeText(MainActivity.this, "看书", Toast.LENGTH_SHORT).show();
                        return true;
                    case R.id.climb_hobby:
                        Toast.makeText(MainActivity.this, "爬山", Toast.LENGTH_SHORT).show();
                        return true;
                    default:
                        return false;
                }
            }
        });
        popupMenu.show();
    }
}

其中，onCreateOptionsMenu方法用于加载菜单布局文件，onOptionsItemSelected方法用于处理菜单项点击事件。showSubjectMenu方法和showHobbyMenu方法分别用于弹出科目菜单和爱好菜单，并且为每个菜单项设置点击事件，使用Toast提示菜单项的内容。

接下来，在res/menu文件夹下，创建以下三个菜单布局文件：

1. main_menu.xml（主菜单）

<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/subject_menu"
        android:title="科目"
        android:icon="@drawable/ic_menu_subject"
        android:showAsAction="always" />
    <item
        android:id="@+id/hobby_menu"
        android:title="爱好"
        android:icon="@drawable/ic_menu_hobby"
        android:showAsAction="always" />
</menu>

2. subject_menu.xml（科目菜单）

<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/java_subject"
        android:title="Java语言"
        android:icon="@drawable/ic_menu_java" />
    <item
        android:id="@+id/python_subject"
        android:title="Python语言"
        android:icon="@drawable/ic_menu_python" />
    <item
        android:id="@+id/android_subject"
        android:title="Android"
        android:icon="@drawable/ic_menu_android" />
</menu>

3. hobby_menu.xml（爱好菜单）

<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/sports_hobby"
        android:title="运动"
        android:icon="@drawable/ic_menu_sports" />
    <item
        android:id="@+id/study_hobby"
        android:title="学习"
        android:icon="@drawable/ic_menu_study" />
    <item
        android:id="@+id/read_hobby"
        android:title="看书"
        android:icon="@drawable/ic_menu_read" />
    <item
        android:id="@+id/climb_hobby"
        android:title="爬山"
        android:icon="@drawable/ic_menu_climb" />
</menu>

其中，ic_menu_subject、ic_menu_hobby、ic_menu_java、ic_menu_python、ic_menu_android、ic_menu_sports、ic_menu_study、ic_menu_read、ic_menu_climb是自定义的菜单图标，可以根据实际情况进行修改。

最终实现效果如下图所示：