Java: Instanceof and Generics

user_147601 0
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Before I look through my generic data structure for a value's index, I'd like to see if it is even an instance of the type this has been parametrized to.

But Eclipse complains when I do this:

@Override
public int indexOf(Object arg0) {
    if (!(arg0 instanceof E)) {
        return -1;
    }

This is the error message:

Cannot perform instanceof check against type parameter E. Use instead its erasure Object since generic type information will be erased at runtime

What is the better way to do it?

instanceof typechecking generics java
9 Answers

Let Java determine it and catch the exception bottom line.

public class Behaviour<T> {
    public void behave(Object object) {
        T typedObject = null;
        
        try { typedObject = (T) object; }
        catch (ClassCastException ignored) {}
        
        if (null != typedObject) {
            // Do something type-safe with typedObject
        }
    }
}
user_37481780
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