在java虚拟机中——第7章类型的生存期——初始化的代码片段如下。

class NewParent {

    static int hoursOfSleep = (int) (Math.random() * 3.0);

    static {
        System.out.println("NewParent was initialized.");
    }
}

class NewbornBaby extends NewParent {

    static int hoursOfCrying = 6 + (int) (Math.random() * 2.0);

    static {
        System.out.println("NewbornBaby was initialized.");
    }
}

class Example2 {

    // Invoking main() is an active use of Example2
    public static void main(String[] args) {

        // Using hoursOfSleep is an active use of NewParent,
        // but a passive use of NewbornBaby
        int hours = NewbornBaby.hoursOfSleep;
        System.out.println(hours);
    }

    static {
        System.out.println("Example2 was initialized.");
    }
}

在上面的例子中，执行example2的main（）只会初始化example2和newparent。新生婴儿未初始化，不需要加载。 Example2 参考文献 NewbornBaby ，我认为应该是“jvm加载” NewbornBaby 一开始它发现 NewbornBaby 没有 hoursOfSleep 字段，然后继续加载 NewbornBaby 的超类 NewParent ". 那么，为什么java虚拟机内部说不需要加载newbornbaby呢？
之后 javac Example2.java ，我跑 java -verbose:class Example2 ，下面是输出的一部分。

[Loaded Example2 from file:/Users/jason/trivial/]
[Loaded sun.launcher.LauncherHelper$FXHelper from /Library/Java/JavaVirtualMachines/jdk1.8.0_181.jdk/Contents/Home/jre/lib/rt.jar]
[Loaded java.lang.Class$MethodArray from /Library/Java/JavaVirtualMachines/jdk1.8.0_181.jdk/Contents/Home/jre/lib/rt.jar]
[Loaded java.lang.Void from /Library/Java/JavaVirtualMachines/jdk1.8.0_181.jdk/Contents/Home/jre/lib/rt.jar]
Example2 was initialized.
[Loaded NewParent from file:/Users/jason/trivial/]
[Loaded NewbornBaby from file:/Users/jason/trivial/]
[Loaded java.lang.Math$RandomNumberGeneratorHolder from /Library/Java/JavaVirtualMachines/jdk1.8.0_181.jdk/Contents/Home/jre/lib/rt.jar]
[Loaded java.util.Random from /Library/Java/JavaVirtualMachines/jdk1.8.0_181.jdk/Contents/Home/jre/lib/rt.jar]
NewParent was initialized.
1

它表明jvm确实加载了 NewbornBaby .