Compiler error with calling Generic methods java

Question

I have created a generic class with few methods. I just want to call the method and add value but its not working. Here is the code

public interface GenericInterface<T> {
    public T getValue();
    public  void setValue(T t);
}

public class FirstGeneric<T> implements GenericInterface<T> {
    private T value;

    public FirstGeneric(T _value) {
        this.value = _value;
    }

    @Override
    public T getValue() {
        return value;
    }

    @Override
    public void setValue(T t) {
        this.value = t;
    }

    @SuppressWarnings("unchecked")
    public static <T> T addValues(FirstGeneric<T> myGeneric, FirstGeneric<T> myGeneric1) {
        T result = null;
        if (myGeneric != null && myGeneric1 != null) {
            T t1 = myGeneric.getValue();
            T t2 = myGeneric1.getValue();
            result = (T) t1.toString().concat(t2.toString());
            System.out.println("Result is:=" + result);
        }
        return result;
    }

    public static void main(String args[]) {
        Integer int1 = 1;
        FirstGeneric<Integer> myInt = new FirstGeneric<Integer>(int1);
        String value = "Hello";
        FirstGeneric<String> myString = new FirstGeneric<String>(value);
        addValues(myString,  myInt);
    }
}

But i am getting compilation error at last line.

The method addValues(FirstGeneric, FirstGeneric) in the type FirstGeneric is not applicable for the arguments (FirstGeneric, FirstGeneric)

What I am doing wrong? Thanks.

Eran · Accepted Answer · 2018-03-26 08:40:19Z

4

addValues has a single generic type parameter, which means you can't pass to it both a FirstGeneric<Integer> and a FirstGeneric<String>.

To make the addValues(myString, myInt) call valid, you can define two generic type parameters in your method:

public static <T,U> String addValues(FirstGeneric<T> myGeneric, FirstGeneric<U> 
   myGeneric1) {
    String result = null;
    if (myGeneric != null && myGeneric1 != null) {
        T t1 = myGeneric.getValue();
        U t2 = myGeneric1.getValue();
        result = t1.toString().concat(t2.toString());
        System.out.println("Result is:=" + result);
    }
    return result;
}

Note that I changed the return type to String, since it's clearly a String (produced by t1.toString().concat(t2.toString())), so you can't cast it to T and hope that T would be a String.

answered Mar 26, 2018 at 8:40

Eran

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