如何给JPanel添加背景图片，超级简单，只需要短短几句话，网上大部分都不可以用，特别坑，你们下载后只用修改图片地址就可以使用了！-How to add a background image to JPanel, super simple, just need just a few words, you can use the Internet most are not, especially in the pit, you download images using only modify t