Question

为什么下面的代码在JDK7中抛出CloneNotSupportedException但在JDK6中？

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();
}

线程从未被设计为克隆。做一些阅读引发了我发现的一条评论，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." - David Holmes

Answer 2

这不起作用，因为无法克隆线程。代码的第16行尝试克隆未实现Cloneable接口的超类（Thread）。除了克隆线程之外根本不是一个好主意。您需要创建一个新线程。这是唯一可行的解决方案。

CloneNotSupportedException即使在实现Cloneable时也是如此

2 个答案: