Class dependency causes stackoverflowerror

public class SchoolServiceImpl {private static SchoolServiceImpl instance = new SchoolServiceImpl();private static ClassServiceImpl classServiceImpl = ClassServiceImpl.getInstanse();public static SchoolServiceImpl getInstanse() {if (instance == null)return instance = new SchoolServiceImpl();return instance;}public int getSchoolCount() {return classServiceImpl.getClassesCount();}    public static void main(String[] args) {System.out.println(classServiceImpl.getClassesCount());}}

public class ClassServiceImpl {/** * @param args */private static ClassServiceImpl instance = new ClassServiceImpl();public static  ClassServiceImpl getInstanse() {if (instance == null)return instance = new ClassServiceImpl();return instance;}private static SchoolServiceImpl schoolServiceImpl=SchoolServiceImpl.getInstanse();public int getClassesCount(){   System.out.println(classServiceImpl.toString());return schoolServiceImpl.getSchoolCount();}}

The above two classes depend on each other's methods, resulting in an endless loop and eventually leading to memory overflow.

Lessons learned: Minimize the dependency between classes and achieve one-way dependency.