Entity Gui Button

I have a button in my Gui for my entity and when I press it I want to change set the xp to 100 for example (xp being a custom variable I have within the entity class). It works when I press the button but then instantly reverts back to the original number.

Is there anything wrong with this?

public void actionPerformed(GuiButton button) {

	if(button.id == 0) {

		entityBlockling.setXP(100);

	}

}