In a class component, you noticed that a child component re-renders unnecessarily even when its props don't change. Which method can be used to prevent the unnecessary re-renders related to state changes?

To prevent unnecessary re-renders of a child component in a class component when its props don't change, you can use the shouldComponentUpdate method. By implementing this method, you can control whether the component should update based on certain conditions. The other methods mentioned (componentDidUpdate, componentWillReceiveProps, and render) have different purposes and are not used for preventing unnecessary re-renders specifically related to state changes.