How is it possible to have ClassCastException after instanceof returns true

Question

I am getting the following code snippet from Android's Pair.java

public boolean equals(Object o) {
    if (o == this) return true;
    if (!(o instanceof Pair)) return false;
    final Pair<F, S> other;
    try {
        other = (Pair<F, S>) o;
    } catch (ClassCastException e) {
        return false;
    }
    return first.equals(other.first) && second.equals(other.second);
}

I was wondering, how is it possible to have ClassCastException, after instanceof returns true.

check your import. Maybe you are importing two different Pair class — Blackbelt
– Blackbelt, Commented Sep 25, 2012 at 14:09
You aren't getting a ClassCastException, are you? It should be impossible in this case. Just because you found code somewhere that catches some random exception doesn't mean this exception can actually be thrown. — David Wasser
– David Wasser, Commented Sep 25, 2012 at 14:33
It's possible your F and/or S class is the one throwing the ClassCastException. Post full code sample or a stack trace, please. — KJP
– KJP, Commented Sep 25, 2012 at 14:47
Full code is already posted as external link in the question. That's the official code from Android — Cheok Yan Cheng
– Cheok Yan Cheng, Commented Sep 25, 2012 at 15:22

artbristol · Accepted Answer · 2012-09-25 14:36:23Z

4

It isn't possible. The code makes no sense. Whoever wrote it probably didn't understand that F and S are erased at runtime so a ClassCastException could never happen.

answered Sep 25, 2012 at 14:36

artbristol

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2 Comments

Cheok Yan Cheng Over a year ago

The code are from Google Android engineers. Possible they see something we don't notice?

Cheok Yan Cheng Over a year ago

Same guess from me. Anyone can go wrong, including Googlers :)

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