How do I fix implementation error in JAVA VS code, “must implement the inherited abstract class”

Question

I am currently learning interfaces, classes and generics.

My current assignment is to create a class which mimics "ArrayLists" in Java. (probably java 7)

this is the interface

I have created a class: public class StudentArrayList implements SimpleArrayList<E> { but I am getting this error: I am getting this error

Error: The type StudentArrayList must implement the inherited abstract method SimpleArrayList<E>.set(int, E)Java(67109264)

I have already implemented all the function signatures in the class, but it is still me asking to implement again and again. How do I fix this issue? please let me know. Thanks!

StudentArrayList.java:

public class StudentArrayList implements SimpleArrayList<E> {

    public static void main(String[] args) {
        System.out.println("Success");
    }

    @Override
    public int size() {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public boolean isEmpty() {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public boolean contains(E o) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public E[] toArray() {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void add(E e) {
        // TODO Auto-generated method stub

    }

    @Override
    public void remove(E o) {
        // TODO Auto-generated method stub

    }

    @Override
    public boolean containsAll(SimpleArrayList<E> c) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public boolean addAll(SimpleArrayList<E> c) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public boolean addAll(int index, SimpleArrayList<E> c) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public boolean removeAll(SimpleArrayList<E> c) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public boolean retainAll(SimpleArrayList<E> c) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public void clear() {
        // TODO Auto-generated method stub

    }

    @Override
    public E get(int index) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void set(int index, E element) {
        // TODO Auto-generated method stub

    }

    @Override
    public void add(int index, E element) {
        // TODO Auto-generated method stub

    }

    @Override
    public void remove(int index) {
        // TODO Auto-generated method stub

    }

    @Override
    public int indexOf(E o) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public int lastIndexOf(E o) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public SimpleArrayList subList(int fromIndex, int toIndex) {
        // TODO Auto-generated method stub
        return null;
    }

}`

Answer 1

You appear to be trying to write a generic class that implements an generic interface. The problem is that you have not actually declared the class as generic. And the compiler therefore things that E is a class name.

The declaration:

public class StudentArrayList implements SimpleArrayList<E> {

should be:

public class StudentArrayList<E> implements SimpleArrayList<E> {

The <E> after StudentArrayList declares E as a type parameter of StudentArrayList .

The compilation errors were probably a result of the compiler thinking that E was a class name (rather than a type parameter) and not being to find any definition for it.