Java 中类的变量、代码块、构造方法加载的顺序

Java 面试 About 2,536 words

加载顺序

  1. 父类静态变量
  2. 父类静态代码块
  3. 子类静态变量
  4. 子类静态代码块
  5. 父类成员变量
  6. 父类代码块
  7. 父类构造方法
  8. 子类成员变量
  9. 子类代码块
  10. 子类构造方法

示例代码

public class Parent {

    public static final ParentStaticFiled PARENT_STATIC_FILED = new ParentStaticFiled();

    public ParentMemberFiled parentMemberFiled = new ParentMemberFiled();

    private String parentMemberVar;

    static {
        System.out.println(LocalDateTime.now() + " Parent static block#" + PARENT_STATIC_FILED);
    }

    {
        System.out.println(LocalDateTime.now() + " Parent non static block#" + parentMemberVar);
    }

    public Parent() {
        parentMemberVar = "pmv";
        System.out.println(LocalDateTime.now() + " Parent Constructor#" + parentMemberVar);
    }
}

public class ParentStaticFiled {

    public ParentStaticFiled() {

        System.out.println(LocalDateTime.now() + " Parent static field");

    }
}

public class ParentMemberFiled {

    public ParentMemberFiled() {

        System.out.println(LocalDateTime.now() + " Parent member field");

    }
}

public class Child extends Parent {

    public static final ChildStaticFiled CHILD_STATIC_FILED = new ChildStaticFiled();

    public String childMemberVar = "cmv";

    public ChildMemberFiled childMemberFiled = new ChildMemberFiled();

    static {
        System.out.println(LocalDateTime.now() + " Child static block#" + CHILD_STATIC_FILED);
    }

    {
        System.out.println(LocalDateTime.now() + " Child non static block#" + childMemberVar);
    }

    public Child() {
        System.out.println(LocalDateTime.now() + " Child constructor#" + childMemberVar);
    }

    public static void main(String[] args) {
        Child child = new Child();
    }

}

public class ChildStaticFiled {

    public ChildStaticFiled() {

        System.out.println(LocalDateTime.now() + " Child static field");

    }
}

public class ChildMemberFiled {

    public ChildMemberFiled() {

        System.out.println(LocalDateTime.now() + " Child member field");

    }
}

输出:

2021-04-19T19:58:34.549045300 Parent static field
2021-04-19T19:58:34.564671500 Parent static block#ParentStaticFiled@402f32ff
2021-04-19T19:58:34.595926100 Child static field
2021-04-19T19:58:34.595926100 Child static block#ChildStaticFiled@5ae9a829
2021-04-19T19:58:34.595926100 Parent member field
2021-04-19T19:58:34.595926100 Parent non static block#null
2021-04-19T19:58:34.595926100 Parent Constructor#pmv
2021-04-19T19:58:34.595926100 Child member field
2021-04-19T19:58:34.595926100 Child non static block#cmv
2021-04-19T19:58:34.595926100 Child constructor#cmv
Views: 1,752 · Posted: 2021-04-19

————        END        ————

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