Class 正在加载，静态块

Question

我有这段代码，我运行它使用 -verbose:class 选项来查看加载的 classes。令我惊讶的是，它显示它已加载 class A1 和 A2，但未调用静态块。

谁能解释一下这种行为

package P1;



import java.lang.reflect.InvocationTargetException;

public class DemoReflection {

    static {
        System.out.println("Loading Demo");
    }

    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException,
            InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        System.out.println("A2 " + A2.class.getClassLoader().getClass());
        System.out.println("Demo " + DemoReflection.class.getClassLoader().getClass());
        System.out.println("A1 " + A1.class.getClassLoader().getClass());
    }

}

class A1 {
    static {
        System.out.println("Loading A1");
    }
}

class A2 extends A1 {

    static {
        System.out.println("Loading A2");
    }

    public A2() {
        System.out.println("m2");
    }

    public void m1() {
        System.out.println("m1");
    }
}

class A3 {

    static int a3Id = 3;

    static {
        System.out.println("Loading A3");
    }

}

输出：

Answer 1

简单版：静态块仅在您第一次创建对象或访问该对象的静态成员时运行 class.

Answer 2

JLS §8.7 说：

A static initializer declared in a class is executed when the class is initialized (§12.4.2).

那么初始化是什么意思呢？在这里引用 JLS §12.4.2. This describes detailed initialization procedure. However point JLS §12.4.1 可能更合适。它说：

A class or interface type T will be initialized immediately before the first occurrence of any one of the following:
T is a class and an instance of T is created.
T is a class and a static method declared by T is invoked.
A static field declared by T is assigned.
A static field declared by T is used and the field is not a constant variable (§4.12.4).
T is a top level class (§7.6), and an assert statement (§14.10) lexically nested within T (§8.1.3) is executed.

这些选项均不适用于您的情况，因此不会调用静态块。

Class 正在加载，静态块

Class Loading, static block

java

static

classloader