Java：无法转换为自定义类

Question

I am creating a Tic-Tac-Toe game in which a square in the grid is represented by a class called Square which I created. It extends JButton, but I added a boolean field called pressable which states whether or not the button can be pressed in-game. If the button already has a letter, then it cannot be pressed. I want to implement code in my actionPerformed() method that will check the pressable variable, and if pressable is false, it will not change the letter of the square. I am using the getSource() method on my ActionEvent to give me a reference to the square pressed. Therefore, I need to cast the Object to type Square so that I can access its pressable field. But when I do this, I get the following error: java.lang.ClassCastException: javax.swing.JButton cannot be cast to tic.tac.toe.Square This makes no sense to me. Before I needed each square to have a pressable field, I used a JButton, which worked just fine. But since Square inherits JButton, I would think that it would work as well. How can I fix this?

Answer 1

The JVM is telling you the truth: the object returned by getSource() is in fact a JButton and is not a Square object, despite your statements above. So the fact is, you are adding your ActionListener to a JButton and not to a Square object. You will need to inspect your code to see why this is so. If you need more of our help, you'll need to show this code.

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Edit
You state:

I looked into it and realized that my "Start" button was going through the same process, which is where the error came from.

Thank you for the update.

This suggests that you're using one ActionListener for all buttons, which you'll not want to do. Certainly all the tic-tac-toe buttons can use the same listener, but any others should use there own separate listener object, perhaps via an anonymous inner class.

Answer 2

You could disable the JButton the first time it is clicked with .setEnabled(false) which would get around this issue. But I agree with HovercraftFullOfEels.