java 引用传值图解

旧城等待， 2022-05-19 04:19 210阅读 0赞

碰到了一个群内求助关于引用传值的问题.

这里把容易混淆的赋值和类传值问题进行详细说明

# 引用修改 #

@Test
        public void testEquals()  {
            Boolean b = new Boolean(false);
            change(b);
            System.out.println(b);
        }
    
        private void change(Boolean b)  {
            b = !b;
        }

关于这个例子的答案,熟练java的你一定知道结果是`false`.

那么这是为什么呢,内存的布局是怎样的呢?

![新建][new1.png]  
错误理解  
![修改堆][changeDui.png]  
实际上  
![新申请空间][new3.png]  
![赋值栈地址][new4.png]

## 疑问解答 ##

为什么不是修改栈的指向?  
![赋值栈地址][question1.jpg]  
因为不是同一个栈地址,按照 黑色->绿色->红色 的顺序去看  
![赋值栈地址][methodStack.png]

# 引用属性修改 #

@Test
         public void testClass()  {
             Student student = new Student();
             student.name = "name";
             changeClassAttr(student);
             System.out.println(student.name);
         }
    
         class Student{
             String name;
         }
         private void changeClassAttr(Student stu)  {
             stu.name = "changeAttr";
         }

![修改属性][classNewStu.png]  
![类新申请空间][changeAttr.png]

# 混淆点 #

根据`引用修改`的理论,那么现在是不是就已经知道这里的答案了呢?

@Test
        public void testClass()  {
            Student student = new Student();
            student.name = "name";
            changeClass(student);
            System.out.println(student.name);
        }
    
        class Student{
            String name;
        }
    
        private void changeClass(Student stu)  {
            stu = new Student();
            stu.name = "changeClass";
        }

[new1.png]: http://cdn.blog.shangwantong.com/java-core/ref/new1.png
[changeDui.png]: http://cdn.blog.shangwantong.com/java-core/ref/changeDui.png
[new3.png]: http://cdn.blog.shangwantong.com/java-core/ref/new3.png
[new4.png]: http://cdn.blog.shangwantong.com/java-core/ref/new4.png
[question1.jpg]: http://cdn.blog.shangwantong.com/java-core/ref/question1.jpg
[methodStack.png]: http://cdn.blog.shangwantong.com/java-core/ref/methodStack.png
[classNewStu.png]: http://cdn.blog.shangwantong.com/java-core/ref/classNewStu.png
[changeAttr.png]: http://cdn.blog.shangwantong.com/java-core/ref/changeAttr.png