Lambda implementation of functional interface returns "unimplemented methods" error - but program works

Question

I am using eclipse to learn Java generics and lambda basics and I encountered a problem with the implementation of functional interface. I wanted to implement the method via lambda expression, but then compiler constantly shows "The type MyGenericClass must implement the inherited abstract method FunctionalIfce.getType()" even though I implemented it via lambda expression and later on even used in a program. When running there are no problems - all of the results are correct but error persists. Everything is within one package. Here are the implementations:

import java.lang.reflect.Type;

@FunctionalInterface
public interface FunctionalIfce {
    Type getType();
}

import java.lang.reflect.Type;

public class MyGenericClass<T extends Number> 
                    implements FunctionalIfce{

    private T value;

    // Lambda implementation of interface
    public FunctionalIfce fIfce = () -> {
        Type parameterType = value.getClass();
        return parameterType;
    };

    public T getValue() {
        return value;
    }

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

    @Override
    public String toString() {
        return "The value is equal: "+value+" and it's type: "+fIfce.getType();
    }

    //Stadard implementation ###  Lambda implementation above
    /*
    @Override
    public Type getType() {
        Type parameterType = value.getClass();
        return parameterType;
    }
    */

}

And from Main class I call it as followed:

    public class AdvancedEntry {

        public static void main(String[] args) {
            MyGenericClass<Integer>  generic = new MyGenericClass<>();
            generic.setValue(5);
            System.out.println(generic.toString());         
        }

    }

Is that an eclipse problem or did I make a mistake in my implementation that magically works? I will really appreciate any help on this puzzle since I found nothing that would remotely look like my issue.

Answer 1

You need to remove the interface implementation and it works.

import java.lang.reflect.Type;

public class MyGenericClass<T extends Number>{

    private T value;

    // Lambda implementation of interface
    public FunctionalIfce fIfce = () -> {
        Type parameterType = value.getClass();
        return parameterType;
    };

    public T getValue() {
        return value;
    }

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

    @Override
    public String toString() {
        return "The value is equal: "+value+" and it's type:    "+fIfce.getType();
    }


    //Stadard implementation ###  Lambda implementation above
    /*
    @Override
    public Type getType() {
        Type parameterType = value.getClass();
        return parameterType;
    }
    */

}