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Editorial Team
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Asked: 2026-05-14T06:16:21+00:00

A number of times I’ve argued that using clone() isn’t such a bad practice.

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A number of times I’ve argued that using clone() isn’t such a bad practice. Yes, I know the arguments. Bloch said it’s bad. He indeed did, but he said that implementing clone() is bad. Using clone on the other hand, especially if it is implemented correctly by a trusted library, such as the JDK, is OK.

Just yesterday I had a discussion about an answer of mine that merely suggests that using clone() for ArrayList is OK (and got no upvotes for that reason, I guess).

If we look at the @author of ArrayList, we can see a familiar name – Josh Bloch. So clone() on ArrayList (and other collections) is perfectly fine (just look at their implementations).

Same goes for Calendar and perhaps most of the java.lang and java.util classes.

So, give me a reason why not to use clone() with JDK classes?

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  1. Editorial Team

    So, give me a reason why not to use clone() with JDK classes?

    • Given an ArrayList reference, you would need a getClass check to check that it is not a subclass of the JDK class. And then what? Potential subclasses cannot be trusted. Presumably a subclass would have different behaviour in some way.
    • It requires that the reference is more specific than List. Some people don’t mind that, but the majority opinion is that that is a bad idea.
    • You’ll have to deal with a cast, an unsafe cast at that.
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