blocks|key|3328803|text|如果可以选择，最好的办法是根本不实现/使用clone()，因为it+is+a+broken+API。只需实现/使用复制构造函数即可。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3328804|如果出于某些迫切的原因，您必须使用clone()，但可以更改其实现，请考虑声明Stack<T>.clone()以返回Stack<T>而不是Object+-协变返回类型在Java5之后是合法的。|3328805|更新：如果有问题的Stack是java.util.Stack，请考虑使用its+Javadoc|BOLD|3328806|Deque接口及其实现提供了一组更完整和一致的后进先出堆栈操作，应该优先于此类使用|3328807|。|blockquote|3328808|3328809|3328810|例如，ArrayDeque提供了copy+constructor。|3328811|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/3410035/how-to-make-a-copy-of-arraylist-object-which-is-type-of-list/3410133#3410133|1|http://download.oracle.com/javase/6/docs/api/java/util/Stack.html|2|http://download.oracle.com/javase/6/docs/api/java/util/Deque.html|3|http://download.oracle.com/javase/6/docs/api/java/util/ArrayDeque.html|4|http://download.oracle.com/javase/6/docs/api/java/util/ArrayDeque.html#ArrayDeque%2528java.util.Collection%2529^0|L|7|V|I|0|0|H|7|13|G|1M|8|1X|6|0|0|3|9|5|F|F|10|B|1|0|0|5|0|5|2|0|0|0|0|3|A|3|A|3|G|G|4|0^^$0|@$1|2|3|4|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@$9|1C|A|1D|1|1E]]|E|$]]|$1|F|3|G|5|6|7|1F|8|@$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]|$9|1M|A|1N|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1O|8|@$9|1P|A|1Q|B|J]|$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]]|D|@$9|1V|A|1W|1|1X]]|E|$]]|$1|K|3|L|5|6|7|1Y|8|@$9|1Z|A|20|B|C]]|D|@$9|21|A|22|1|23]]|E|$]]|$1|M|3|N|5|O|7|24|8|@]|D|@]|E|$]]|$1|P|3|-4|5|6|7|25|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|26|8|@]|D|@]|E|$]]|$1|R|3|S|5|6|7|27|8|@$9|28|A|29|B|C]]|D|@$9|2A|A|2B|1|2C]|$9|2D|A|2E|1|2F]]|E|$]]|$1|T|3|-4|5|6|7|2G|8|@]|D|@]|E|$]]]|U|$V|$5|W|X|Y|E|$Z|10]]|11|$5|W|X|Y|E|$Z|12]]|13|$5|W|X|Y|E|$Z|14]]|15|$5|W|X|Y|E|$Z|16]]|17|$5|W|X|Y|E|$Z|18]]]]

If you have the choice, the best is not to implement / use <code>clone()</code> at all, because <a href="https://stackoverflow.com/questions/3410035/how-to-make-a-copy-of-arraylist-object-which-is-type-of-list/3410133#3410133">it is a broken API</a>. Just implement / use a copy constructor instead.

If for some pressing reason you must use <code>clone()</code> but can change its implementation, consider declaring <code>Stack&lt;T&gt;.clone()</code> to return <code>Stack&lt;T&gt;</code> instead of <code>Object</code> - covariant return types are legal since Java5.

Update: if the <code>Stack</code> in question is <code>java.util.Stack</code>, consider <a href="http://download.oracle.com/javase/6/docs/api/java/util/Stack.html" rel="nofollow noreferrer">its Javadoc</a>:

<blockquote>
 A more complete and consistent set of LIFO stack operations is provided by the <a href="http://download.oracle.com/javase/6/docs/api/java/util/Deque.html" rel="nofollow noreferrer"><code>Deque</code></a> interface and its implementations, which should be used in preference to this class.
</blockquote>

And e.g. <a href="http://download.oracle.com/javase/6/docs/api/java/util/ArrayDeque.html" rel="nofollow noreferrer"><code>ArrayDeque</code></a> provides a <a href="http://download.oracle.com/javase/6/docs/api/java/util/ArrayDeque.html#ArrayDeque%28java.util.Collection%29" rel="nofollow noreferrer">copy constructor</a>.

blocks|key|1926146|text|这里是无法避免演员阵容的。clone()返回Object，如果是java.util.Stack，则不使用协变返回类型。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1926147|如果这不是java.util.Stack，那么就不要实现clone()+--这真的很难让它正确。改为创建一个复制构造函数。|1926148|entityMap^0|D|7|M|6|W|F|0|5|F|S|7|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|I|$]]

There is no way to avoid the cast here. <code>clone()</code> returns <code>Object</code>, if it is <code>java.util.Stack</code>, it is not making use of co-variant return types.

If this is not <code>java.util.Stack</code>, then don't implement <code>clone()</code> - it's really hard to get it right. Make a copy-constructor instead.

blocks|key|1926111|text|你别无选择，只能忽略它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1926112|虽然不是直接相关的(因为您不是在编写clone()方法)，但Java+Generics+FAQ中的这个条目读起来很好(整个常见问题解答也是如此！)|offset|length|style|CODE|1926113|entityMap|0|LINK|mutability|MUTABLE|url|http://www.angelikalanger.com/GenericsFAQ/FAQSections/ProgrammingIdioms.html#FAQ502^0|0|I|7|U|H|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@$D|R|E|S|F|G]]|9|@$D|T|E|U|1|V]]|A|$]]|$1|H|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

You have very little choice but to ignore it.

Whilst not directly relevant (because you're not writing a <code>clone()</code> method), this entry in the <a href="http://www.angelikalanger.com/GenericsFAQ/FAQSections/ProgrammingIdioms.html#FAQ502" rel="nofollow">Java Generics FAQ</a> makes good reading (as does the whole FAQ!)

blocks|key|1930918|text|是的，每次使用clone()时，您都需要显式地取消警告。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1930919|这是您可能更喜欢使用复制构造函数而不是clone()的原因之一。|1930920|顺便说一下，在您的代码中，当使用RawStringIterator(RawStringIterator+i)构造函数时，stateStack的第一次初始化是不必要的：|1930921|class+RawStringIterator+{
++++Stack<State>+stateStack+=+new+Stack<State>();
++++RawStringIterator(RawStringIterator+i)+{
++++++++++stateStack+=+(Stack<State>)+i.stateStack.clone();
++++}
++++/*+...+*/
}|code-block|syntax|javascript|1930922|你可能想把它去掉。|1930923|entityMap^0|7|7|0|J|7|0|G|12|1O|A|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@$9|W|A|X|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|13|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|14|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|R|$]]

Yes, you'll need to explicitly suppress the warnings each time you use <code>clone()</code>.

This is one of the reasons you might prefer to use copy constructors instead of <code>clone()</code>, if available.

By the way in your code, when the <code>RawStringIterator(RawStringIterator i)</code> constructor is used, the first initialisation of <code>stateStack</code> is unnecessary:

<pre><code>class RawStringIterator {
 Stack&lt;State&gt; stateStack = new Stack&lt;State&gt;();
 RawStringIterator(RawStringIterator i) {
 stateStack = (Stack&lt;State&gt;) i.stateStack.clone();
 }
 /* ... */
}
</code></pre>

You might want to remove that.

This code:

<pre><code>class RawStringIterator {
 java.util.Stack&lt;State&gt; stateStack = new java.util.Stack&lt;State&gt;();
 RawStringIterator(RawStringIterator i) {
 stateStack = (java.util.Stack&lt;State&gt;) i.stateStack.clone();
 }
 /* ... */
}
</code></pre>

gives me this warning:

<pre><code>Type safety: Unchecked cast from Object to Stack&lt;Utils.OperatorTree.RawStringIterator.State&gt;
</code></pre>

I guess I can ignore the warning here. But I wonder about how to use <code>clone()</code> in general? Do I always have to use a <code>@SuppressWarnings("unchecked")</code> every time I use <code>clone()</code>? Or should I always do the completely redundant extra check?

java: how to use clone() and what about the cast check

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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这段代码：class RawStringIterator { java.util.Stack<State> stateStack = new java.util.Stack<State>(); RawStringIterator(RawStringIterator i) { stateStack = (java.util.Stack<State

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