为什么我的静态代码块不执行？ [英] Why doesn't my static block of code execute?

问题描述

我正在尝试运行此代码，但我发现了final的这种行为与静态：代码运行时没有执行A的静态块。请提供原因。

I am trying to run this code, I but found out this behavior of final with static: the code runs without executing static block of A. Please provide me with the reason.

class A {
  final static int a=9;
    static { //this block is not executing ??
      System.out.println("static block of A");
     }
}

class Manager {
  static {
    System.out.println("manager sib");
  }

  public static void main(String ...arg) {
    System.out.println("main");
    System.out.println(A.a);
  }
}

为什么A类的静态块不运行？

Why doesn't the static block of Class A run?

推荐答案

问题是 Aa 是常量变量。

原始类型或类型String的变量，是最终的并使用编译时常量表达式（第15.28节）初始化，称为常量变量。

A variable of primitive type or type String, that is final and initialized with a compile-time constant expression (§15.28), is called a constant variable.

因此您的 Manager.main 方法已完全编译 好像它是：

Therefore your Manager.main method is compiled exactly as if it were:

public static void main(String ...arg) {
    System.out.println("main");
    System.out.println(9);
}

没有真正的参考 Aa 以上，所以 A 类甚至不需要存在，更不用说初始化了。 （您可以删除 A.class 并仍然运行经理。）

There's no real reference to A.a any more, so the A class doesn't even need to exist, let alone be initialized. (You can delete A.class and still run Manager.)

如果您依赖于使用 Aa 来确保类型已初始化，则不应添加no-op方法：

If you're relying on using A.a to make sure the type is initialized, you shouldn't add a no-op method instead:

public static void ensureClassIsInitialized() {
} 

然后从 main 方法中调用 。尽管如此，这是非常不寻常的。

then just call that from your main method. It's very unusual to need to do this though.

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