Pass by What ?

Nic Sense Zone — Thu, 13 Apr 2006 04:07:00 GMT

�?/span> Java 中值类型和引用�c�d��是如何进行传递的�Q�这个是我今天要谈论话题�?/span>

关于�q�个话题�Q�我的一个好友的推荐下看了一��文章，�q�才使我有了写这��文章的��x��。这��文章是�?/span> Pass-by-Value Please �?/span> (http://www.javaranch.com/campfire/StoryPassBy.jsp) �Q�顺便再向大家推荐一个网站，��是 http://www.javaranch.com �Q�一个很好的 Java 乐园�?/span>

好了�Q�回到正题吧～免得一下又跑远了～呵呵·

关于值类型，我想大家都很清楚了，�ȝ��说来��是 Copy the value and give it to you �?/span>

��L��如下代码�Q?br />

�l�果如下�Q?/span>

a= 2

b= 2

=============== the value has changed ===============

a= 3

b= 2

�q�个例子很明显，不用�q�多的解释， a �?/span> b 已经是两个独立的�Q�互补相�q�的倹{�?/span>

下面�q�入我们今天的重点，关于引用�c�d��?/span>

我这里想借鉴一下我开��提到的那篇文章�Q�里面提到的杯子�Q?/span> I like the cap, do you?

在这里，我想打一个比方，把我们杯子里的引�?/span> Reference 作一个类��|��在操作系�l�里�Q�有一个很重要的概念，那就�?b style="mso-bidi-font-weight: normal">�q�程控制�?/span>�Q�他是进�E�实体的一部分�Q�是操作�pȝ��中最重要的记录型数据�l�构�Q�他记录了操作系�l�所需的，用于描述�q�程的当前情况以及控制进�E�运行的全部信息。同��P��引用也是如此�Q�只是没有这么复杂�Ş了。引用里存放�?/span> java object 的相关信息，以便�?/span> JVM (Java Virtual Machine) 在堆中找到对�?/span> (Java 对象全部在堆�?/span> ) �?/span>

我们可以把这�U�情冉|��象成在一个杯子里放了一个类��g��q�程控制块的 reference �Q�下面来看如下代码：

1 package blog.nichlas.article.j2se;
2
3 import static java.lang.System.out;
4
5 public class PassByValue {
6     public static void testPassValue(){
7         int a = 2 ;
8         int b = a ;
9         out.println("a= " + a ) ;
10         out.println("b= " + b ) ;
11         out.println("=============== the value has changed ===============");
12         a = 3 ;  // has change the value of a, but tht value of b is never be changed
13         out.println("a= " + a ) ;
14         out.println("b= " + b ) ;
15     }
16
17     public static void testPassReference(){
18         ObjectForTest o1 = new ObjectForTest("Object one");
19         ObjectForTest o2 = o1;
20         out.println(o1.getInfo());
21         out.println(o2.getInfo());
22         out.println("=============== the value has changed ===============");
23         o1 = new ObjectForTest("Object two");
24         out.println(o1.getInfo());
25         out.println(o2.getInfo());
26     }
27
28     public static void main(String [] args){
29         out.println();
30         PassByValue.testPassValue();
31         out.println();
32         PassByValue.testPassReference();
33     }
34 }
35
36 class ObjectForTest{
37     String info ;
38
39     public ObjectForTest(){
40         info = "default";
41     }
42
43     public ObjectForTest(String initInfo){
44         info = initInfo ;
45     }
46
47     public String getInfo(){
48         return info;
49     }
50
51     public void setInfo(String changeInfo){
52         info = changeInfo;
53     }
54 }

�q�行�l�果是：

a= 2

b= 2

=============== the value has changed ===============

a= 3

b= 2

Object one

=============== the value has changed ===============

Object two

Object one

�q�里可以很明昄��表示出其实所谓的 Reference 其实��p��值类型是很相似的�Q�所以我们可以给 Reference 取一个名字�?b style="mso-bidi-font-weight: normal">引用�?/span>”�?/span>

�q�里只是�?/span> o1 的引用值拷贝了一份给 o2 �?/span>

不过�q�里要注意的��是虽然是引用值的拯��Q�但他们却引用了同一个对象，��M��一个对对象的改变都会，在另外一个引用上都可以显�C�的出来�?br />看如下的例子�Q?br />

1 package blog.nichlas.article.j2se;
2
3 import static java.lang.System.out;
4
5 public class PassByValue {
6     public static void testPassValue(){
7         int a = 2 ;
8         int b = a ;
9         out.println("a= " + a ) ;
10         out.println("b= " + b ) ;
11         out.println("=============== the value has changed ===============");
12         a = 3 ;  // has change the value of a, but tht value of b is never be changed
13         out.println("a= " + a ) ;
14         out.println("b= " + b ) ;
15     }
16
17     public static void testPassReference(){
18         ObjectForTest o1 = new ObjectForTest("Object one");
19         ObjectForTest o2 = o1;
20         out.println(o1.getInfo());
21         out.println(o2.getInfo());
22         out.println("=============== the value has changed ===============");
23         o1 = new ObjectForTest("Object two");
24         out.println(o1.getInfo());
25         out.println(o2.getInfo());
26     }
27
28     public static void testChangeObject(){
29         ObjectForTest o1 = new ObjectForTest("Object one");
30         ObjectForTest o2 = o1;
31         out.println(o1.getInfo());
32         out.println(o2.getInfo());
33         out.println("=============== the value has changed ===============");
34         o1.setInfo("Object Value changed!");
35         out.println(o1.getInfo());
36         out.println(o2.getInfo());
37     }
38
39     public static void main(String [] args){
40         out.println();
41         PassByValue.testPassValue();
42         out.println();
43         PassByValue.testPassReference();
44         out.println();
45         PassByValue.testChangeObject();
46     }
47 }
48
49 class ObjectForTest{
50     String info ;
51
52     public ObjectForTest(){
53         info = "default";
54     }
55
56     public ObjectForTest(String initInfo){
57         info = initInfo ;
58     }
59
60     public String getInfo(){
61         return info;
62     }
63
64     public void setInfo(String changeInfo){
65         info = changeInfo;
66     }
67 }

�l�果如下�Q?/span>

a= 2

b= 2

=============== the value has changed ===============

a= 3

b= 2

Object one

=============== the value has changed ===============

Object two

Object one

=============== the value has changed ===============

Object Value changed

从这里可以看刎ͼ� o1 对对象的改变体现在了 o2 上了�Q�通过�?/span> o2 的调用可以看出�?/span>

以上是我对这个问题的看法�Q�希望大家可以给一点帮助�?/span>

Nic Sense Zone 2006-04-13 12:07 发表评论

��的使用

Nic Sense Zone — Wed, 18 Jan 2006 04:21:00 GMT

摘要: 1. 关于OutputStream �?write�Q�int�Q�方�?public abstract void write(int b) throws IOException 此方法接受一个不大于255的整��C��为参敎ͼ��q�将其以相应的byte输出到outputStream�?不知读者有没有惌��Z��么要求int型的参数��于2... 阅读全文

Nic Sense Zone 2006-01-18 12:21 发表评论

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Pass by What ?

���的使用

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