使用参数化类的Java泛型问题

Question

All! I have breaking my head over this things for a few hours now. I'm sorry if it's something so trivial but I guess I don't understand Java generics well enough. I'm a novice Java programmer.

I have 2 interfaces. Int1 and Int2. Int2 extends Int1. Int2Impl implements Int2. Lesson1.java and AnotherClass.java are given below also. Questions follow after the classes.

Int1.java

     public interface Int1<E> {
           public Lesson1<E> interfaceimpl(Class<E> klass);
     }

Int2.java

     public interface Int2<E> extends Int1<E> {
         String getSomething();
     }

Lesson1.java

    public class Lesson1<E> {

    }

Int2Impl.java

    public class Int2Impl<E> implements Int2<E> {
        Class<E> klass;

        @Override
        public String getSomething() {
          return "nothing";
        }

        @Override
        public Lesson1<E> interfaceimpl(Class<E> klass) {
            this.klass = klass;
            return null;
        }
   }

AnotherClass.java

  public class AnotherClass<E> {
        private Int2<E> interface2; 

        private <E> void newMethod(Class<E> klass) {
            interface2 = new Int2Impl<>();
          **interface2.interfaceimpl(klass);**

      }
   }

The line of code that's causing a compilation issue is,

interface2.interfaceimpl(klass); in the class AnotherClass.java

the errors and the quickfixes that Eclipse offers are:

Error:

  The method interfaceimpl(java.lang.Class<E>) in the type Int1<E> is not 
  applicable for the arguments (java.lang.Class<E>)

Quick Fixes:

1) Change method interfaceImpl(Class<E>) to interface(Class<E>) 
2) Cast Argument klass to Class<E> 
3) Change type of klass to Class<E>
4) Create method interfaceImpl(Class<E>) in type 'Int2'

None of the quick fixes make sense to me. Plus they also don't fix the problem regardless of which one I choose. Can someone point out the mistake and why Eclipse throws this error?

Thanks!

Answer 1

Your AnotherClass is already of generic type E . No need to define E again at method level.

Just remove <E> from your newMethod() as follows:

public class AnotherClass<E> {
    private Int2<E> interface2;

    private void newMethod(Class<E> klass) {
        interface2 = new Int2Impl<>();
        interface2.interfaceimpl(klass);

    }
}