Following the online teacher’s learning, I typed a simplified traditional Chinese conversion code as follows:
found the seventh line of code error, and moved the mouse to the code. The method covertotraditional (string) is undefined for the type zhconverterutil. In fact, it’s a jar package error. The zhconverterutil class in the jar package has no coverttotraditional method

we just need to change coverttotraditional to totraditional to complete the conversion from simplified to traditional Chinese

summary: if you report any error in this aspect in the future, you can go to the jar package to see if there is such a method.