Java访问修饰符原理及代码解析

一、概述

访问等级比较：public > protected > default > private

无论是方法还是成员变量，这四种访问权限修饰符作用都一样

• public:不管包外包内，所有类（子类+非子类）均可使用
• protected
  • 包内：所有类可使用
  • 包外：子类可使用，非子类不可使用
• default
  • 包内：所有类可使用
  • 包外：所有类不可使用
• private：仅本类可使用
  

二、示例代码

test包内的父类permission

public class permission {
  private int privatevalue = 1;
  public int publicvalue = 1;
  protected int protectedvalue = 1;
  int defaultvalue = 1;
  
  void defaultfunc(){
    system.out.println("this is a default function");
  }
  
  public void publicfunc(){
    system.out.println("this is a public function");
  }
  
  protected void protectedfunc() {
    system.out.println("this is a protected function");
  }

  private void privatefunc(){
    system.out.println("this is a private function");
  }
}

test包内的子类subpermission

public class subpermission extends permission{
  public void permissiontest(){
    // public, protected, default function and variable can be used
    system.out.println("this is a default value:" + this.defaultvalue);
    system.out.println("this is a public value:" + this.publicvalue);
    system.out.println("this is a protected value:" + this.protectedvalue);

    this.publicfunc();
    this.protectedfunc();
    this.defaultfunc();
  }
}

test包外的子类

import base.test.permission;

public class demo extends permission {
  public static void main(string[] args) {
    // if is not a subclass, only public function and variable can be used
    permission obj = new permission();
    obj.publicfunc();
    system.out.println("this is a public value:" + obj.publicvalue);

    // if is a subclass, public and protected function and variable can ba used
    demo demo = new demo();
    demo.publicfunc();
    demo.protectedfunc();
    system.out.println("this is a public value:" + demo.publicvalue);
    system.out.println("this is a protected value:" + demo.protectedvalue);
  }
}

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