为什么在使用 .getSource() 方法时将 ChangeEvent 对象转换为 JSlider？

Question

The book I'm learning from is going through event listeners and I'm confused about casting a ChangeEvent object to a JSlider object when using the event.getSource() method. Why is this necessary?

Secondarily, does casting or method calling take precedence? It seems like the method call occurs first if the .getSource() method is a ChangeEvent method.

I apologize for the single line of code but that's all the book has to offer outside of simple explicit directions to cast the ChangeEvent to a JSlider:

"This method is called with a ChangeEvent object that can identify the slider component that changed in cale. Call the object's getSource() method and cast the object to a JSlider, as in the following statement:" (followed by the code below with no explanation why to cast it).

JSlider changedSlider = (JSlider) event.getSource();

Answer 1

That doesn't cast the event to JSlider . It casts the source of the event to JSlider .

The source of the event is the slider which has fired the event.

And the cast is probably necessary because the rest of the code needs to access the JSlider properties/methods.