需要在服务端的onBind方法中返回一个IBinder对象，同时在客户端中调用bindService方法时传入ServiceConnection对象，通过ServiceConnection的回调方法得到服务端返回的IBinder对象。以下是示例代码：

服务端代码：

public class MyService extends Service {
    private final IBinder binder = new MyBinder();

    @Override
    public IBinder onBind(Intent intent) {
        return binder;
    }

    public class MyBinder extends Binder {
        public MyService getService() {
            return MyService.this;
        }
    }

    public int getRandomNumber() {
        return new Random().nextInt(100);
    }
}

客户端代码：

public class MainActivity extends AppCompatActivity {
    private MyService myService;
    private boolean isBound = false;

    private ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
            MyService.MyBinder binder = (MyService.MyBinder) iBinder;
            myService = binder.getService();
            isBound = true;
            Log.d(TAG, "Service connected");
        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {
            isBound = false;
            Log.d(TAG, "Service disconnected");
        }
    };

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

        Intent intent = new Intent(this, MyService.class);
        bindService(intent, connection, BIND_AUTO_CREATE);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (isBound) {
            unbindService(connection);
            isBound = false;
        }
    }

    public void onClick(View view) {
        if (isBound) {
            int number = myService.getRandomNumber();
            Toast.makeText(this, "Random number: " + number, Toast.LENGTH_SHORT).show();
        }
    }
}