When viewing the class or interface of the system called in the program, I hold down the Ctrl key and then click the class or interface with the mouse. The source code is not displayed, but source not found.
After checking on Baidu for a while, I want to install the plug-in, but then I think about it, I am looking for the API of the system, there is no need to install it, and then I find this method:
In the interface that displays the source not found error, there is a button to select Externalam location, and then select External File. Under your JDK installation path, find the src.zip file, which is usually together with the bin and lib folders.
Once selected, it will be displayed.
Purely moving bricks, for beginners reference!