代码块详解

青旅半醒 2023-10-01 19:17 27阅读 0赞

## 1.基本介绍 ##

![在这里插入图片描述][61e67cc274bf4fbf83d30f23f4586ddb.png]  
**基本语法**  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBASmF2YeeahOWtpuS5oOS5i-i3rw_size_20_color_FFFFFF_t_70_g_se_x_16]  
**代码块的好处**  
1.相当于另外一种形式的构造器((对构造器的补充机制)，可以用来做初始化的操作  
2.场景：如果多个构造器中都有重复的语句，可以抽取到初始化块中，提高代码的复用性

package codeblock;
    
    
    public class code1 {
        
        public static void main(String[] args) {
        
            new Movie();
            System.out.println("----------------------");
            new Movie("tom");
            System.out.println("----------------------");
            new Movie("jack","jim");
            System.out.println("----------------------");
            new Movie("jacky","tim",20);
        }
    }
    
    class Movie{
        
        private String name;
        private String director;
        private double price;
    
        {
        
            System.out.println("电影开始");
            System.out.println("准备观看");
        }
        public Movie() {
        
            System.out.println("无参构造器被调用");
        }
    
        public Movie(String name) {
        
            System.out.println("Movie(String name)被调用");
            this.name = name;
        }
    
        public Movie(String name, String director) {
        
            System.out.println("Movie(String name,String director)被调用");
            this.name = name;
            this.director = director;
        }
    
        public Movie(String name, String director, double price) {
        
            System.out.println("Movie(String name,String director,double price)被调用");
            this.name = name;
            this.director = director;
            this.price = price;
        }
    }

执行结果  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBASmF2YeeahOWtpuS5oOS5i-i3rw_size_20_color_FFFFFF_t_70_g_se_x_16 1]

如果构造器当中有相同的语句，我们可以把这些语句放在代码块中，不然会显得代码冗余
    这样子不管我们调用哪一个构造器，创建对象，都会先调用代码块的内容
    代码块调用顺序优先于构造器

## 2.代码块使用的注意事项 ##

**代码块先执行，构造器再执行**  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBASmF2YeeahOWtpuS5oOS5i-i3rw_size_16_color_FFFFFF_t_70_g_se_x_16]

package  codeblock;
    
     
    public class code2 {
        
        public static void main(String[] args) {
        
            new A();
        }
    }
    class A{
        
        static {
        
            System.out.println("静态代码块A执行");
        }
        {
        
            System.out.println("代码块A执行");
        }
        public A(){
        
            System.out.println("构造器A执行");
        }
    
    }

执行结果:

静态代码块A执行
    代码块A执行
    构造器A执行

package com.zyh.codeblock;
    
    /**
     * @author zengyihong
     * @create 2022--02--20 9:22
     */
    public class code2 {
        
        public static void main(String[] args) {
        
            //new A();
            new B();
        }
    }
    class A{
        
        static {
        
            System.out.println("静态代码块A执行");
        }
        {
        
            System.out.println("代码块A执行");
        }
        public A(){
        
            System.out.println("构造器A执行");
        }
    
    }
    
    class B extends A{
        
    
        static {
        
            System.out.println("静态代码块B执行");
        }
        {
        
            System.out.println("代码块B执行");
        }
    
    
    }

执行结果:  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBASmF2YeeahOWtpuS5oOS5i-i3rw_size_7_color_FFFFFF_t_70_g_se_x_16]  
**静态代码块随着类的加载而加载，并且只会加载一次，代码块随着对象的创建，每创建一次，都会调用一次**

package  codeblock;
    
     
    public class code2 {
        
        public static void main(String[] args) {
        
            //new A();
            new B();
            System.out.println("-------------------");
            new B();
        }
    }
    class A{
        
        static {
        
            System.out.println("静态代码块A执行");
        }
        {
        
            System.out.println("代码块A执行");
        }
        public A(){
        
            System.out.println("构造器A执行");
        }
    
    }
    
    class B extends A{
        
    
        static {
        
            System.out.println("静态代码块B执行");
        }
        {
        
            System.out.println("代码块B执行");
        }
    
    
    }

![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBASmF2YeeahOWtpuS5oOS5i-i3rw_size_11_color_FFFFFF_t_70_g_se_x_16]  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBASmF2YeeahOWtpuS5oOS5i-i3rw_size_15_color_FFFFFF_t_70_g_se_x_16]

package codeblock;
    
    public class code3 {
        
      public static void main(String[] args) {
        
    
        D d = new D();// (1) A 静态代码块 01 (2) getN1 被调用...(3)A 普通代码块 01(4)getN2 被调用...(5)A()  构造器被调
    
      }
    }
    
    class D {
        
       //普通代码块
    
     {
        
      System.out.println("A 普通代码块 01");
     }
    
     private int n2 = getN2();//普通属性的初始化
    
    
     private static    int n1 = getN1();
     static {
         //静态代码块
      System.out.println("D 静态代码块 01");
     }
    
     //静态属性的初始化
    
     public static int getN1() {
        
      System.out.println("getN1 被调用...");
      return 100;
     }
    
     public int getN2() {
         //普通方法/非静态方法
      System.out.println("getN2 被调用...");
      return 200;
     }
     //无参构造器
     public D() {
        
      System.out.println("A()  构造器被调用");
     }
    }

![在这里插入图片描述][2800db50bd404138b50b409b26cddfd1.png]  
![在这里插入图片描述][8ab5f03499cb4cf7a7b92a0838b122f7.png]

package codeblock;
    
    public class CodeBlockDetail03 {
        
        public static void main(String[] args) {
        
            //(1)AAA 的普通代码块(2)AAA()  构造器被调用(3)BBB 的普通代码块(4)BBB()  构造器被调用 }
            new BBB();
        }
    }
        class AAA {
         //父类 Object
            {
        
                System.out.println("AAA 的普通代码块");
            }
    
            public AAA() {
        
    //(1)super()
    //(2)调用本类的普通代码块
                System.out.println("AAA()  构造器被调用....");
            }
    
    
        }
    
       class BBB extends AAA {
        
            {
        
                System.out.println("BBB 的普通代码块...");
            }
    
            public BBB() {
        
    //(1)super()
    //(2)调用本类的普通代码块
                System.out.println("BBB()  构造器被调用....");
            }
        }

![在这里插入图片描述][899dbd333e6d4480a5a6eec2a747ea5b.png]  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBASmF2YeeahOWtpuS5oOS5i-i3rw_size_18_color_FFFFFF_t_70_g_se_x_16]

静态代码块只能调用静态属性，静态方法，而普通代码块可以调用任何成员

注:本文是学习韩顺平老师的课程所写

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[2800db50bd404138b50b409b26cddfd1.png]: https://img-blog.csdnimg.cn/2800db50bd404138b50b409b26cddfd1.png
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