“{}”中的主类块从不执行
考虑以下代码：-
class Name {
{System.out.println("hi");}
public static void main(String[] args) {
System.out.println(waffle());
}
static boolean waffle() {
try {
return true;
} finally {
return false;
}
}
}
这永远不会输出“hi”。这是为什么呢？
Consider the following code:-
class Name {
{System.out.println("hi");}
public static void main(String[] args) {
System.out.println(waffle());
}
static boolean waffle() {
try {
return true;
} finally {
return false;
}
}
}
This never outputs "hi" . Why is this?
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评论（3）
大括号中的代码是 实例初始值设定项。
来自 Java 语言规范，第三版，< a href="http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.6" rel="nofollow noreferrer">第 8.6 节：
如果执行
Name类，Java虚拟机会调用public static void main(String[])方法，但是Name类不是未实例化的，因此实例初始化程序中的代码永远不会被执行。还有一个 静态初始化程序，外观与实例初始值设定项类似，但前面有
static关键字：同样，来自 Java 语言规范，第三版，第 8.7 节：
初始化字段页面来自 Java 教程 还包含有关静态和实例初始值设定项块的信息。
The code in the braces is the instance initializer.
From The Java Language Specification, Third Edition, Section 8.6:
If the
Nameclass is executed, thepublic static void main(String[])method is called by the Java virtual machine, but theNameclass is not is not instantiated, so the code in the instance initializer will never be executed.There is also a static initializer, which is similar in appearance to the instance initializer, but it has the
statickeyword in front:Again, from The Java Language Specification, Third Edition, Section 8.7:
The Initializing Fields page from The Java Tutorials also has information about the static and instance initializer blocks.
我认为它仅在实例创建时激活。尝试将其作为 static { ... } 运行
I think it is activated only on instance creation. Try running it as static { ... }
该块应该声明为 static 才能运行，即 static{System.out.println("hi");}
The block should be declared static to get it to run, i.e. static{System.out.println("hi");}