Java值传递机制

布满荆棘的人生 2023-02-20 08:23 86阅读 0赞

# 一、针对于方法内变量的赋值举例 #

/** * Description: * * @author zygui * @date Created on 2020/6/25 19:21 */
    public class VarTest { 
        public static void main(String[] args) { 
    
            System.out.println("***********基本数据类型：****************");
    
            int m = 10;
            int n = m;
            System.out.println("m = " + m + ", n = " + n);  // 很简单, m = 10, n = 10;
    
            n = 20;
            System.out.println("m = " + m + ", n = " + n);  // 很简单, m = 10, n = 20;
    }

public class VarTest2 { 
    
            System.out.println("***********引用数据类型：****************");
    
            Order o1 = new Order();
            o1.orderId = 1001;
            Order o2 = o1; //赋值以后，o1和o2的地址值相同，都指向了堆空间中同一个对象实体。
            System.out.println("o1.orderId = " + o1.orderId + ", o2.orderId = " +o2.orderId); // 1001, 1001
    
            o2.orderId = 1002;
            // 因为指向的是同一地址空间, 当o2修改该空间中的orderId后, o1的orderId也随之改变
            System.out.println("o1.orderId = " + o1.orderId + ", o2.orderId = " +o2.orderId); // 1002, 1002
    
        }
    }
    
    class Order { 
        int orderId;
    }

# 二、针对于方法的参数概念 #

*  形参：方法定义时，声明的小括号内的参数
 *  实参：方法调用时，实际传递给形参的数据

# 三、Java中参数传递机制：值传递 #

规则：

*  如果参数是`基本数据类型`，此时实参赋给形参的是实参真实存储的`数据值`。
 *  如果参数是`引用数据类型`，此时实参赋给形参的是实参存储数据的`地址值`。

推广：

*  如果变量是基本数据类型，此时赋值的是变量所保存的数据值。
 *  如果变量是引用数据类型，此时赋值的是变量所保存的数据的地址值。

##### 传递基本数据类型 #####

public class VarTest { 
        public static void main(String[] args) { 
            int m = 10;
            int n = 20;
            System.out.println("m = " + m + ", n = " + n);
            VarTest vt = new VarTest();
            vt.swap(m, n);
            System.out.println("m = " + m + ", n = " + n); // 10, 20;
    
        }
    
        public void swap(int m, int n){ 
            int temp = m;
            m = n;
            n = temp;
            // System.out.println("m = " + m + ", n = " + n); // 20, 10
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70]

##### 传递引用数据类型 #####

public class VarTest { 
        public static void main(String[] args) { 
            Data data = new Data();
            data.m = 10;
            data.n = 20;
            System.out.println("m = " + data.m + ", n = " + data.n);
    
            // int temp = data.m;
            // data.m = data.n;
            // data.n = temp;
            // System.out.println("m = " + data.m + ", n = " + data.n); // 20, 10
    
            VarTest vt = new VarTest();
            vt.swap(data); // 传的是data的地址值; 它们指向的是同一块内存空间
            System.out.println("m = " + data.m + ", n = " + data.n);
        }
    
        public void swap(Data data) { 
            int temp = data.m;
            data.m = data.n;
            data.n = temp;
            System.out.println("m = " + data.m + ", n = " + data.n); // 20, 10
        }
    }
    
    class Data { 
        int m;
        int n;
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 1]

### 练习 ###

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 2]  
内存图如下  
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