Java开发网 - Re:对象的调用，为什么一定要使用静态的成员变量

Java开发网

您没有登录

» Java开发网 » Java SE 综合讨论区

打印话题 寄给朋友 订阅主题

作者

Re:对象的调用，为什么一定要使用静态的成员变量 [Re:athen]

andyforcjsdn

发贴: 1
积分: 0

于 2005-05-01 02:46

Hi,

First of all, pls forgive me use english to talk to you, it is because i don't know any chinese input method. Your question is quite interesting, i think many Java newbies may face the same problem, to solve it we should understand that there are two fields in Java, one is Class Field another is Instance Field.

Definition of Class Fields:

A Class Field is associated with the class in which it is defined, rather than with an instance of the class. The key point to understand about a static field is that there is only a single copy of it. This field is associated with the class itself, not with instances of the class. (excerpt from Java in a nutshell, chapter 3, Object-Oriented Programming in Java - Class Fields).
http://www.unix.org.ua/orelly/java-ent/jnut/ch03_01.htm

So you can access class variables (fields) through an instance or through the class itself.

For example:

class X
{
static int x=12; // class field
void put(int y){
System.out.println(y);
}
public static void main(String[] args)
{

X a = new X();
System.out.println(a.x); //accessing through an instance
System.out.println(X.x); //accessing through the class itself

}
}

Definition of Instance Fields:

Instance fields are associated with instances of the class, rather than with the class itself.
Thus, every X object (instance) we create has its own copy of the int field x.
So you can access an instance member only through a reference to an instance.

For example,

class X
{
int x=12; // instance field
void put(int y){
System.out.println(y);
}
public static void main(String[] args)
{

X a = new X();
System.out.println(a.x); // only accessing through an instance
System.out.pringln(X.x); // illegal
Systme.out.println(x); // illegal
}
}

Pls also refer to http://java.sun.com/docs/books/tutorial/java/javaOO/classvars.html
i hope it will be helpful for you, good luck.

andy

andyforcjsdn edited on 2005-05-01 09:26

• 25了才开始学JAVA晚吗？

话题树型展开

人气	标题	作者	字数	发贴时间
6663	对象的调用，为什么一定要使用静态的成员变量	athen	373	2005-04-29 20:57
5353	Re:对象的调用，为什么一定要使用静态的成员变量	bluepure	51	2005-04-30 00:40
5392	Re:对象的调用，为什么一定要使用静态的成员变量	lancelob	11	2005-04-30 09:26
5416	Re:对象的调用，为什么一定要使用静态的成员变量	vicious	18	2005-04-30 14:01
5518	Re:对象的调用，为什么一定要使用静态的成员变量	andyforcjsdn	1972	2005-05-01 02:46
5344	Re:对象的调用，为什么一定要使用静态的成员变量	jinguizi	119	2005-05-01 18:50
5399	Re:对象的调用，为什么一定要使用静态的成员变量	wan9721	169	2005-05-11 16:53
5393	Re:对象的调用，为什么一定要使用静态的成员变量	dengyinjun	57	2005-05-25 03:05

已读帖子

新的帖子

被删除的帖子