弄懂局部变量和成员变量的内存位置

红太狼 2024-03-16 12:02 13阅读 0赞

### 成员变量和局部变量的区别 ###

![259763d6d795470eb5acac41a5f432c2.png][]

**成员变量**(*Member Variables*) **局部变量**（Local Variable）

### 测试局部变量和成员变量在内存中的位置 ###

#### 1.上测试代码 ####

@Service
    public class User {
        private final  static int a1 = 1;
        private final  static String b1 = "你";
        private final  static int[] c1 = {1,2,3};
        private int d1 = 2;
        private String e1 = "好";
        private int[] f1 = {4,5,6};
    
        public void aa() {
            int d1 = 2;
            System.out.println("User的aa()的d1" + "  值  " +d1+  "  内存  " + System.identityHashCode(d1));
            String e1 = "好";
            System.out.println("User的aa()的e1" + "  值  " +e1+  "  内存  " + System.identityHashCode(e1));
            int[] f1 = {4,5,6};
            System.out.println("User的aa()的f1" + "  值  " +f1+  "  内存  " + System.identityHashCode(f1));
        }
        public void bb() {
            int d1 = 2;
            System.out.println("User的bb()的d1" + "  值  " +d1+  "  内存  " + System.identityHashCode(d1));
            String e1 = "好";
            System.out.println("User的bb()的e1" + "  值  " +e1+  "  内存  " + System.identityHashCode(e1));
            int[] f1 = {4,5,6};
            System.out.println("User的bb()的f1" + "  值  " +f1+  "  内存  " + System.identityHashCode(f1));
        }
    
        public static int getA1() {
            return a1;
        }
    
        public static String getB1() {
            return b1;
        }
    
        public static int[] getC1() {
            return c1;
        }
    
        public  int getD1() {
            return d1;
        }
    
        public  String getE1() {
            return e1;
        }
    
        public  int[] getF1() {
            return f1;
        }
    }

@Service
    public class Nat {
        private final  static int a1 = 1;
        private final  static String b1 = "你";
        private final  static int[] c1 = {1,2,3};
        private int d1 = 2;
        private String e1 = "好";
        private int[] f1 = {4,5,6};
    
        public void aa() {
            int d1 = 2;
            System.out.println("Nat的aa()的d1" + "  值  " +d1+  "  内存  " + System.identityHashCode(d1));
            String e1 = "好";
            System.out.println("Nat的aa()的e1" + "  值  " +e1+  "  内存  " + System.identityHashCode(e1));
            int[] f1 = {4,5,6};
            System.out.println("Nat的aa()的f1" + "  值  " +f1+  "  内存  " + System.identityHashCode(f1));
        }
        public void bb() {
            int d1 = 2;
            System.out.println("Nat的bb()的d1" + "  值  " +d1+  "  内存  " + System.identityHashCode(d1));
            String e1 = "好";
            System.out.println("Nat的bb()的e1" + "  值  " +e1+  "  内存  " + System.identityHashCode(e1));
            int[] f1 = {4,5,6};
            System.out.println("Nat的bb()的f1" + "  值  " +f1+  "  内存  " + System.identityHashCode(f1));
        }
    
        public static int getA1() {
            return a1;
        }
    
        public static String getB1() {
            return b1;
        }
    
        public static int[] getC1() {
            return c1;
        }
    
        public  int getD1() {
            return d1;
        }
    
        public  String getE1() {
            return e1;
        }
    
        public  int[] getF1() {
            return f1;
        }
    }

@RestController
    @RequestMapping("/aaa")
    public class Qqq {
    @Autowired
    private User user;
        @Autowired
        private Nat nat;
        @GetMapping("/bbb")
        public void ccc() {
            
            System.out.println("User的a1" + "  值  " +User.getA1()+  "  内存  " + System.identityHashCode(User.getA1()));
            System.out.println("User的b1" + "  值  " +User.getB1()+  "  内存  " + System.identityHashCode(User.getB1()));
            System.out.println("User的c1" + "  值  " +User.getC1()+  "  内存  " + System.identityHashCode(User.getC1()));
            System.out.println("User的d1" + "  值  " +user.getD1()+  "  内存  " + System.identityHashCode(user.getD1()));
            System.out.println("User的e1" + "  值  " +user.getE1()+  "  内存  " + System.identityHashCode(user.getE1()));
            System.out.println("User的f1" + "  值  " +user.getF1()+  "  内存  " + System.identityHashCode(user.getF1()));
            user.aa();
            user.bb();
    
            System.out.println("Nat的a1" + "  值  " +Nat.getA1()+  "  内存  " + System.identityHashCode(Nat.getA1()));
            System.out.println("Nat的b1" + "  值  " +Nat.getB1()+  "  内存  " + System.identityHashCode(Nat.getB1()));
            System.out.println("Nat的c1" + "  值  " +Nat.getC1()+  "  内存  " + System.identityHashCode(Nat.getC1()));
            System.out.println("Nat的d1" + "  值  " +nat.getD1()+  "  内存  " + System.identityHashCode(nat.getD1()));
            System.out.println("Nat的e1" + "  值  " +nat.getE1()+  "  内存  " + System.identityHashCode(nat.getE1()));
            System.out.println("Nat的f1" + "  值  " +nat.getF1()+  "  内存  " + System.identityHashCode(nat.getF1()));
            nat.aa();
            nat.bb();
        }
    }

#### 2.运行结果 ####

> <table> 
> <tbody> 
> <tr> 
> <td style="vertical-align:middle;width:52.7pt;">User的a1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:78.35pt;">值&nbsp; 1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:49.95pt;">内存&nbsp; 697815822</td> 
> <td style="vertical-align:middle;width:98.1pt;"></td> 
> <td style="vertical-align:middle;width:91px;">Nat的a1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:63px;">值&nbsp; 1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:49.95pt;">内存&nbsp; 697815822</td> 
> <td style="vertical-align:middle;width:49.95pt;"></td> 
> <td style="vertical-align:middle;width:86.1pt;"></td> 
> <td style="vertical-align:middle;width:49.95pt;"></td> 
> <td style="vertical-align:middle;width:49.95pt;"></td> 
> <td style="vertical-align:middle;width:49.95pt;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;">User的b1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; 你&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 1403028226</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;">Nat的b1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:63px;">值&nbsp; 你&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 1403028226</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;">User的c1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; [I@2feff326&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 804254502</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;">Nat的c1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:63px;">值&nbsp; [I@55f2d93a&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 1441978682</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;"></td> 
> <td style="vertical-align:middle;width:63px;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;"></td> 
> <td style="vertical-align:middle;width:63px;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;">User的d1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; 2&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 387698249</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;">User的aa()的d1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:63px;">值&nbsp; 2&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 387698249</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;">User的bb()的d1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; 2&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 387698249</td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;">User的e1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; 好&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 225287</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;">User的aa()的e1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:63px;">值&nbsp; 好&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 225287</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;">User的bb()的e1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; 好&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 225287</td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;">User的f1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; [I@576c4b96&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 1466715030</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;">User的aa()的f1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:63px;">值&nbsp; [I@3402bcd0&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 872594640</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;">User的bb()的f1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; [I@3ac55420&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 986010656</td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;"></td> 
> <td style="vertical-align:middle;width:63px;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;"></td> 
> <td style="vertical-align:middle;width:63px;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;">Nat的d1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; 2&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 387698249</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;">Nat的aa()的d1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:63px;">值&nbsp; 2&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 387698249</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;">Nat的bb()的d1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; 2&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 387698249</td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;">Nat的e1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; 好&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 225287</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;">Nat的aa()的e1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:63px;">值&nbsp; 好&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 225287</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;">Nat的bb()的e1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; 好&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 225287</td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> <tr> 
> <td style="vertical-align:middle;">Nat的f1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; [I@60f718e9&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 1626806505</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;width:91px;">Nat的aa()的f1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;width:63px;">值&nbsp; [I@3efad7a0&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 1056626592</td> 
> <td style="vertical-align:middle;"></td> 
> <td style="vertical-align:middle;">Nat的bb()的f1&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">值&nbsp; [I@7bf85e1b&nbsp;&nbsp;</td> 
> <td style="vertical-align:middle;">内存&nbsp; 2079874587</td> 
> <td style="vertical-align:middle;"></td> 
> </tr> 
> </tbody> 
> </table>

#### 3.结果分析 ####

首先声明,我额外试验了,局部变量用final修饰和不用final修饰对指向的值的内存地址没有任何影响.因此上面的结果就没有出现用final修饰的局部变量

内存结果分析就是下面我画的图,都在图里面的

![2f2580facc2c4b2a905a47f2956dfb4a.png][]

#### 4.对上图结果分析总结 ####

**成员变量的内存位置**:

1.用final修饰的成员变量,也叫常量.比如final int a=1.这个"a"和"a"指向1的指向,是存在运行时常量池中.

2.没用final修饰的成员变量,比如final int a=1.这个"a"和"a"指向1的指向,是存在方法区的类的信息下面的.

**局部变量的内存位置**:

1.用final修饰的局部变量,比如int a=1.这个"a"和"a"指向1的指向,百度说是存在栈中的,但是不知道存在栈的哪一块.

2.没用final修饰的成员变量,比如int a=1.这个"a"和"a"指向1的指向,是存在栈的方法自己的栈帧中的局部变量表里的.

[259763d6d795470eb5acac41a5f432c2.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/b011ecc2f500417c99f639df94ec15f8.png
[2f2580facc2c4b2a905a47f2956dfb4a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/8b59b325c10b43f5a34fa36fce1f55ae.png