java.lang.Object 中的“shadow$_klass_”和“shadow$_monitor_”变量是什么

"shadow$_klass_"和"shadow$_monitor_"变量是Java中Object类中的两个特殊变量。这两个变量实际上是由JVM（Java虚拟机）在运行时为每个对象动态生成的，并且对于开发者来说是不可见的。它们被用于实现Java中的一些底层机制，如对象的锁定和类型信息。

java
public class ObjectDemo {
    public static void main(String[] args) {
        Object obj = new Object();
        // 获取对象的类类型
        Class klass = obj.getClass();
        System.out.println("Class: " + klass);
        // 获取对象的元数据信息
        Object shadowKlass = getShadowKlass(obj);
        System.out.println("Shadow Klass: " + shadowKlass);
        // 对象锁定和解锁
        synchronized (obj) {
            Object shadowMonitor = getShadowMonitor(obj);
            System.out.println("Shadow Monitor: " + shadowMonitor);
            // 执行同步操作
            // ...
        }
    }
    private static Object getShadowKlass(Object obj) {
        return getObjectField(obj, "shadow$_klass_");
    }
    private static Object getShadowMonitor(Object obj) {
        return getObjectField(obj, "shadow$_monitor_");
    }
    private static Object getObjectField(Object obj, String fieldName) {
        try {
            Field field = getObjectField(obj.getClass(), fieldName);
            field.setAccessible(true);
            return field.get(obj);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
    private static Field getObjectField(Class klass, String fieldName) throws NoSuchFieldException {
        if (klass != null) {
            try {
                return klass.getDeclaredField(fieldName);
            } catch (NoSuchFieldException e) {
                return getObjectField(klass.getSuperclass(), fieldName);
            }
        }
        throw new NoSuchFieldException(fieldName);
    }
}