The second line of the error message says you are trying to add a JLabel to what the third error line is reporting as a List of JButton objects.

　　錯誤消息的第二行表明，您嘗試將一個(gè)JLabel添加到第三個(gè)錯誤行報告的JButton對象的List。

　　Then, if you try to add a JLabel to that collection, the compiler picks up the discrepancy and complains at compile time.

　　然后，如果想要將JLabel添加到集合，則編譯器會(huì )在編譯時(shí)發(fā)現差異和并拋出異常。