为什么此 Java 代码位于方法外部的大括号 ({}) 中? [英] Why is this Java code in curly braces ({}) outside of a method?

问题描述

我正在为 Java 认证考试做准备，我在其中一个练习测试中看到过类似这样的代码:

I am getting ready for a java certification exam and I have seen code LIKE this in one of the practice tests:

class Foo {  
    int x = 1;  
    public static void main(String [] args) {  
        int x = 2;  
        Foo f = new Foo();  
        f.whatever();  
    }  
    { x += x; }  // <-- what's up with this?
    void whatever() {  
        ++x;  
        System.out.println(x);  
    }  
}

我的问题是......在方法外用花括号编写代码是否有效?这些(如果有的话)有什么影响?

My question is ... Is it valid to write code in curly braces outside a method? What are the effects of these (if any)?

推荐答案

借用 这里 -

通常情况下，您会将用于初始化实例变量的代码放在构造函数.使用构造函数有两种选择初始化实例变量:初始化块和最终方法.实例变量的初始化块看起来就像静态的初始化块，但没有 static 关键字:

Normally, you would put code to initialize an instance variable in a constructor. There are two alternatives to using a constructor to initialize instance variables: initializer blocks and final methods. Initializer blocks for instance variables look just like static initializer blocks, but without the static keyword:

{
    // whatever code is needed for initialization goes here
} 

Java 编译器将初始化块复制到每个构造函数中.因此，这种方法可以用于在多个构造函数之间共享一个代码块.

The Java compiler copies initializer blocks into every constructor. Therefore, this approach can be used to share a block of code between multiple constructors.

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