EnumSingelton.java

  public enum PersonEnum {
    INSTANCE;
    
    private int age = 2;

    public int getAge() {
      return age;
    }

    public void setAge(int newAge) {
      this.age = newAge;
    }

  public static void main(String[] args) {

  }
}

  class Test {
    public static void main(String[] args) {
      PersonEnum personEnum = PersonEnum.INSTANCE;
      System.out.println(personEnum.getAge());
      System.out.println(personEnum.getAge());
      personEnum.setAge(10);
      System.out.println(personEnum.getAge());
      personEnum.setAge(11);

      System.out.println(personEnum.getAge());
    }
  }