[Java]对象初始化顺序

2018-05-16  本文已影响0人  猎手Andy

父类:

package effectivejava;

import java.util.ArrayList;
import java.util.List;

public class Person {

    public Person()
    {
        name = "Tom";
               System.out.println("父类构造函数 name is "+name + "  "+this.toString()+"  "+ this.getClass().getName());

    }
    private String name ;
    //初始化块
    {
        name = "Jack";
        System.out.println("父类初始化块 name is "+name + "  "+this.toString());
    }
    //初始化常量数组
    private final static List<String> titles;
    static //静态区初始化
    {
        titles = new ArrayList<String>();
        titles.add("Junior");
        titles.add("Senior");
        titles.add("Expert");
        System.out.println("父类静态初始化块 titles is "+titles);
    }
    
    protected void sayHelloTo(String name)
    {
        System.out.println("父类方法 hello "+name+ "  "+this.toString());
    }
}

子类:

package effectivejava;

public class Student extends Person {

    private static final String teacher;
    public Student()
    {
        className = "Class 1A";
        System.out.println("子类构造函数 class name is "+className+ "  "+this.toString() +"  "+ this.getClass().getName());
    }
    private String className;
    {
        className = "一(2)班";
        System.out.println("子类初始化块 class name is "+className+ "  "+this.toString());
    }
    static {
        teacher = "Chinese Teacher";
        System.out.println("子类静态初始化块 teacher name is "+teacher);
    }
    
    protected void sayHelloTo(String name)
    {
        System.out.println("子类方法 say hello "+name+ "  "+this.toString());
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Student o = new Student();
        o.sayHelloTo("Jack Li");
        //o = new Student();
    }
    
}

运行结果:

父类静态初始化块 titles is [Junior, Senior, Expert]
子类静态初始化块 teacher name is Chinese Teacher
父类初始化块 name is Jack  effectivejava.Student@33909752
父类构造函数 name is Tom  effectivejava.Student@33909752  effectivejava.Student
子类初始化块 class name is 一(2)班  effectivejava.Student@33909752
子类构造函数 class name is Class 1A  effectivejava.Student@33909752  effectivejava.Student
子类方法 say hello Jack Li  effectivejava.Student@33909752

结论:

1. 静态初始化块

     先父类静态初始化块
     再子类静态初始化块

2. 初始化块和构造函数

     先父类初始化块和构造函数
     再子类初始化块和构造函数

注意在父类构造函数或初始化块时的this是子类的对象地址,此时的对象类型是Student而不是Person。

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