Android Studio: open specific app from own app

Question

I have a problem and I cant figure it out. (I am new in android studio) Maybe someone can help me. I have search on the internet but I can't find a solution.

I using Android Studio 1.4

I want to open aan specific app from my own app. So if I lauch my app I see a few buttons. When I press one of the buttons, an specific app will be open.

the problem is that when I press the button. I receive the message: app is stopped.

What I have done: Created a new project and place an button on the main activity.

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="New Button"
    android:id="@+id/button1"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true" />

The in the MainActivity.java I add the following lines:

public class MainActivity extends AppCompatActivity {

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

    Button button = (Button) findViewById(R.id.button1);

    button.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            Intent i = new Intent();
            i.setClassName("com.android.calculator2",
                    "com.android.calculator2.Calculator");
            startActivity(i);
        }
    });

Can please someone help me to solve this problem?

Kind regards