在Java中使用static关键字创建对象 [英] Creating object using static keyword in Java

问题描述

class abc {
    int a = 0;
    static int b;
    static abc h = new abc(); //line 4

    public abc() {
        System.out.println("cons");
    }

    {
        System.out.println("ini");
    }

    static {
        System.out.println("stat");
    }
}

public class ques {
    public static void main(String[] args) {
        System.out.println(new abc().a);
    }
}

当我写这段代码时，我按顺序输出像这样：

When i wrote this code I am getting output in order like this:

ini
cons
stat
ini
cons
0

这时我在 main（）中创建了一个新对象， class abc 已加载， static 变量和块按写入顺序执行。当控制进入第4行 static abc h = new abc（）; 调用实例初始化块。为什么？为什么在第4行创建一个新对象时没有调用静态块，直到那时静态块也没有被调用一次，所以根据惯例静态块应该被调用。为什么会出现意外输出？

Here when I created a new object in main(), class abc got loaded and static variables and blocks are executed in order they are written. When control came to line 4 static abc h = new abc(); Instance Initialization block is called. Why? why is static block not called when a new object is created at line 4 and till that time static block was also not called even once, so according to convention static block should have been called. Why is this unexpected output coming?

推荐答案

静态字段初始化和静态块按声明的顺序执行。在您的情况下，代码在分离声明和初始化后等效于此：

Static fields initialization and static blocks are executed in the order they are declared. In your case, the code is equivalent to this after separating declaration and initialization:

class abc{
    int a;
    static int b;
    static abc h;//line 4

    static {
        h = new abc();//line 4 (split)
        System.out.println("stat");
    }

    public abc() {
        a = 0;
        System.out.println("ini");
        System.out.println("cons");
    }
}

public class ques{
    public static void main(String[] args) {
        System.out.println(new abc().a);
    }
}

所以当你从你的代码到达第4行时，静态初始化实际上正在执行但尚未完成。因此，在 stat 可以打印之前调用构造函数。

So when you reach line 4 from your code, the static initialization is actually being executed and not finished yet. Hence your constructor is called before stat can be printed.

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