java - CloneNotSupportedException 即使在实现 Cloneable 时也是如此

Question

为什么以下代码在 JDK7 中抛出 CloneNotSupportedException 而在 JDK6 中不抛出？

public class DemoThread extends Thread implements Cloneable {

    /**
     * @param args
     */
    public static void main(String[] args) {
        DemoThread t = new DemoThread();
        t.cloned();
    }

    public DemoThread cloned()
    {
        try {
            return (DemoThread) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return null;
    }

}

Answer 1

这是 Thread 在 SE 7 中对 clone() 的实现

/**
 * Throws CloneNotSupportedException as a Thread can not be meaningfully
 * cloned. Construct a new Thread instead.
 *
 * @throws  CloneNotSupportedException
 *          always
 */
@Override
protected Object clone() throws CloneNotSupportedException {
    throw new CloneNotSupportedException();
}

线程从未被设计为被克隆。做一些阅读引发了其中一条评论，我发现这总结得很好:"But we either have to disallow cloning or give it meaningful semantics - and the latter isn't going to happen." -- 大卫·霍姆斯