CODEWITHSUNDEEP
javagenericsinteger
bluehallu
bluehallu

Reputation: 10295

Java Generics problems

I have this class Entry...

public class Entry <K, V> {
    private final K mKey;
    private final V mValue;

    public Entry() {  
        mKey = null;
        mValue = null;   
    }
}

What happens if I use an int as the mKey? As far as I know ints can't be null!

Upvotes: 1

Views: 203

Answers (3)

Michael Berry
Michael Berry

Reputation: 72399

Generic type parameters need to be objects, they can't be primitives. So you can use the Integer wrapper class around mKey / mValue and set it to null, but trying to use the int primitive will always give you a compilation error.

Upvotes: 0

dty
dty

Reputation: 18998

You can't use primitives as type parameters.

Upvotes: 1

Mark Peters
Mark Peters

Reputation: 81154

A variable of type Integer can be null. An int cannot be null. The latter is the primitive type, the former is a wrapper reference type for dealing with primitives as an Object. If you're using this:

Entry<Integer, String> myEntry;

Then you are necessarily using the wrapper type. Primitives can't be used as type parameters in Java so you can't have Entry<int, String> for example (it won't compile).

Upvotes: 6

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