你必须向JLabel提供一个 Icon 实现（即 ImageIcon ）。您可以通过 setIcon 方法（如您的问题）或通过 JLabel 构造函数执行此操作：

You have to supply to the JLabel an Icon implementation (i.e ImageIcon). You can do it trough the setIcon method, as in your question, or through the JLabel constructor:

Image image=GenerateImage.toImage(true);  //this generates an image file
ImageIcon icon = new ImageIcon(image); 
JLabel thumb = new JLabel();
thumb.setIcon(icon);

我建议你阅读 JLabel ， 图标 ，以及 ImageIcon 。另外，您可以查看如何使用标签教程，更多信息。

I recommend you to read the Javadoc for JLabel, Icon, and ImageIcon. Also, you can check the How to Use Labels Tutorial, for more information.