静态修饰符和静态块之间的区别 [英] Difference between static modifier and static block

问题描述

有人向我解释了以下两个陈述之间的区别吗？

Someone explain to me the differences between the following two statements?

一个静态最终变量由a初始化 static 代码块：

A static final variable initialized by a static code block:

private static final String foo;
static { foo = "foo"; }

由一个初始化的静态最终变量赋值：

A static final variable initialized by an assignment:

private static final String foo = "foo";

推荐答案

在这个例子中，有一个微妙的差异 - 在您的第一个示例中， foo 未确定为编译时常量，因此不能用作<$ c中的大小写$ c>切换块（并且不会内联到其他代码中）;在你的第二个例子中，它是。例如：

In this example, there's one subtle difference - in your first example, foo isn't determined to be a compile-time constant, so it can't be used as a case in switch blocks (and wouldn't be inlined into other code); in your second example it, is. So for example:

switch (args[0]) {
    case foo:
        System.out.println("Yes");
        break;
}

当 foo 被认为是一个常量表达式，但不是当它只是一个静态的最终变量时。

That's valid when foo is deemed to be a constant expression, but not when it's "just" a static final variable.

但是，静态初始化程序块通常是当您有更复杂的初始化代码时使用 - 例如填充集合。

However, static initializer blocks are usually used when you have more complicated initialization code - such as populating a collection.

初始化的计时在 JLS 12.4.2 ;任何被认为是编译时常量的静态最终字段首先被初始化（步骤6）并且初始化器被稍后运行（步骤9）;所有初始化程序（无论它们是字段初始化程序还是静态初始化程序）都以文本顺序运行。

The timing for initialization is described in JLS 12.4.2; any static final fields which are considered as compile-time constants are initialized first (step 6) and initializers are run later (step 9); all initializers (whether they're field initializers or static initializers) are run in textual order.

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