问题：
Is there anything like static class in java? java中是否有类似static class东西？
What is the meaning of such a class. 这样的课是什么意思。 Do all the methods of the static class need to be static too? 静态类的所有方法是否也必须是static ？
Is it required the other way round, that if a class contains all the static methods, shall the class be static too? 是否需要反过来，如果一个类包含所有静态方法，那么该类也应该是静态的吗？
What are static classes good for? 静态类有什么用？
解决方案：
参考一： https://stackoom.com/question/VPS8/Java中的静态类
参考二： https://oldbug.net/q/VPS8/Static-Classes-In-Java