How do we call a method located in another activity? 

 

For example I'm trying to use this method from the "MainActivity"

public void change () {
    ConstraintLayout layout = findViewById(R.id.main_layout);
    layout.setBackgroundResource(R.drawable.wallpaper);

}

into the second activity (SecondActivity) when clicking a button

I tried this 

MainAcitvity MA = new MainActivity();

MA.change();

 

but it didn't work. what's the correct way to do it in Android?