类是java程序的组织单位，任何的java语句，都要写在类文件里面。（这么说不全对，package语句和import语句就可以写在外面，但编译之后一定是在类文件里面的）-Class is a java program organization unit, any Java statement, write in the class file. (that s not all right, package, and import statements can be written on the outside, but after the compiler must be in the class file.)