CODEWITHSUNDEEP
javagenerics
Nicholas Newell
Nicholas Newell

Reputation: 97

Fixing error in java: incompatible types: java.lang.Object cannot be converted to capture#1 of?

My code declares a value variable of type Object:

final Object value;

This variable is then loaded with an object.

A generic collection variable is then declared and loaded:

final Collection<?> c = (Collection<?>) argumentDefinition.getFieldValue();

The collection variable is generic in both instances above, with brackets and a question mark that don't pass through in this text.

When I try to use the add method of the collection:

c.add(value)

I get the error message:

java: incompatible types:java.lang.Object cannot be converted to capture #1 of ?

The add method is declared in Collection as:

boolean add(E e);

How can I fix the error? I think I understand what's going on - the compiler creates a placeholder for the generic type that Object isn't compatible with. I can't use a raw type for the collection because I'm trying to eliminate raw types in the code. Do I need to use a helper function, and if so how exactly? Thank you.

Upvotes: 6

Views: 23434

Answers (4)

guest
guest

Reputation: 1

just cast to E before -- this may solve the problem

boolean add(E (E)e);

Upvotes: -1

Vasile Rotaru
Vasile Rotaru

Reputation: 452

You should do the following:

((Collection<Object>)c).add(value);

Then the code will compile and run.

Upvotes: -2

kavi temre
kavi temre

Reputation: 1321

You can replace ? with Object. i think it will work

import java.util.ArrayList;
import java.util.Collection;

public class KaviTemre {
    final Object value="kavi";
    public static void main(String[] args) {
    new KaviTemre().myMethod();
    }
    void myMethod()

    {
        Collection<Object> obj = new ArrayList<Object>();
        final Collection<Object> c = (Collection<Object>)obj;
        c.add(value);

        for(Object o:c)
            System.out.println(o.toString());
    }
}

Upvotes: 0

Eli
Eli

Reputation: 337

It's hard to tell what exactly your problem is without knowing what argumentDefinition.getFieldValue() returns, but a possible solution would be change your variable type from Collection<?> to Collection<Object>.

Upvotes: 5

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