I helped my classmates solve the problem today, and found that I still can’t remember this point, so I edited this article to deepen my memory, and hope to help more friends.
As shown in the red box in the figure below, there is already a drop-down arrow on the left side of my datepicker.jar package. If not , what should I do?
Right-click the package that you want to add a drop-down arrow, and there are many options. In the red frame area in the figure below, there is an option of "add to library" , ( because I already have a drop-down arrow, so the options page I screenshot is the same as no drop-down The option page of the arrow is different ) Click it. Then a prompt box will pop up, just click OK (forgot to take a screenshot). After completing these two steps, a drop-down clipper will appear on the left side of the bag.
