How to do it...

1. Since the Android Studio New Project wizard has already created the first activity, we just need to create the second activity. Open the ActivitySwitcher project and navigate to File | New | Activity | Empty Activity, as shown in this screenshot:

2. In the New Android Activity dialog, you can leave the default Activity Name as is, or change it to SecondActivity, as follows:

3. Open the MainActivity.java file and add the following function:

    public void onClickSwitchActivity(View view) { 
        Intent intent = new Intent(this, SecondActivity.class); 
        startActivity(intent); 
    }

4. Now, open the activity_main.xml file located in the res/layout folder and replace the <TextView /> with the following XML to create the button:

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:text="Launch Second Activity"
        android:onClick="onClickSwitchActivity"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

5. You can run the code at this point and see the second activity open. We're going to go further and add a button to SecondActivity to close it, which will bring us back to the first activity. Open the SecondActivity.java file and
   add this function:

    public void onClickClose(View view) { 
        finish(); 
    } 

6. Finally, add the Close button to the SecondActivity layout. Open the activity_second.xml file and add the following <Button> element to the auto-generated ConstraintLayout: 

    <Button
        android:id="@+id/buttonClose"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Close"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:onClick="onClickClose"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

7. Run the application on your device or emulator and see the buttons in action.