CODEWITHSUNDEEP
javacompiler-errors
Jordan Elpern-Waxman
Jordan Elpern-Waxman

Reputation: 53

compiler says method is undefined ... but it is (I thought)

I'm trying to call:

public class Counter<MyClassSelectorObject> {

    final HashMap<MyClassSelectorObject, Integer> counts = new HashMap<>();

    public void add(MyClassSelectorObject t) {
        counts.merge(t, 1, Integer::sum);
        t.setCount(counts.get(t));
    }
...
}

However I'm getting the following error from my compiler in Eclipse on t.setCount(counts.get(t));:

The method setCount(Integer) is undefined for the type MyClassSelectorObject

However I have 

public class MyClassSelectorObject implements Comparable<MyClassSelectorObject>{

    ...

    public void setCount(Integer value) {
        this.count = value;
    }

    ...

}

The solution that Eclipse's quickfix feature offers me is to cast t to an Object, which makes no sense to me. Then again, I'm just getting back into coding after years away so I might be missing something basic here.

I'm using Java 8 and Eclipse Luna.

Thanks!

Upvotes: 1

Views: 269

Answers (1)

Boris the Spider
Boris the Spider

Reputation: 61148

What you have done is declared a generic class that has a generic type parameter:

public class Counter<T> {

}

Except your T is called MyClassSelectorObject...

So you have shadowed your class with a generic type parameter, you method is equivalent to:

public void add(T t) {
    counts.merge(t, 1, Integer::sum);
    t.setCount(counts.get(t));
}

As there are no bounds on T, the T is equivalent to Object.

As you have already noted, removing the generic type from Counter fixes your problem. Which begs the questions - why did you add it in the first place ...?

Upvotes: 3

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