java 什么是类常量？
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What is a class constant?
提问by Kyle
I am told to declare and initialize my class constant. I didn't know what it was so I searched google, apparently everyone already knows what it is and nobody has asked on it. So what is a class constant? Is it just a value that doesn't change throughout the class?
我被告知要声明并初始化我的类常量。我不知道它是什么所以我搜索了谷歌，显然每个人都已经知道它是什么并且没有人问过它。那么什么是类常量呢？它只是一个在整个类中都不会改变的值吗？
采纳答案by Elliott Frisch
JLS-8.3.1.1. staticFieldssays (in part)
JLS-8.3.1.1。static字段说（部分）
A
staticfield, sometimes called a class variable, is incarnated when the class is initialized (§12.4).
一个
static字段，有时也称为类变量，在类被初始化时体现出来（第12.4 节）。
JLS-4.12.4. finalVariablessays (in part)
JLS-4.12.4。final变量说（部分）
A constant variableis a
finalvariable of primitive type or typeStringthat is initialized with a constant expression (§15.28)
甲常量变量是
final原始类型或类型的变量String，其与一个常量表达式初始化（§15.28）
tl;dr
tl;博士
Putting that together, a class constant is a static finalfield.
综上所述，类常量就是一个static final字段。
回答by duffymo
Class variables are static; instance variables are not.
类变量是静态的；实例变量不是。
Final variables are constant.
最终变量是常数。
So a class constant would be declared like this:
所以一个类常量会像这样声明：
public class Foo {
// Class constant
public static final String DEFAULT_NAME = "Bar";
public static void main(String [] args) {
String name = Foo.DEFAULT_NAME;
}
}
It's the same for all instances of Foo.
的所有实例都是一样的Foo。
