Android : OnClick Method Scope

Somehow I can see the onClick Methods from other activities in my project. I do not know why, but it seems like they are set global.

Now I have a onButtonOkClick method in my current activity and an onButtonOkClick in the previous activity and I get a NullPointerException because it tries to access the one from the previous activity.

Where can I configure that scope? Apparently the onClick methods have to be public also?

public void onButtonOkClick(View view) {
    // CODE
}

I can also see all elements like EditText and Buttons from other Activities in the resources (R.id). Maybe I misconfigured this somewhere?