Question

I am trying to implement the Java 1.6 Queue interface, but I am getting the error:

MyBoundedQueue.java:27: MyBoundedQueue is not abstract and does not override abstract method offer(java.lang.Object) in java.util.Queue

What I really don’t understand is that there is no offer(Object) method in the Queue class. The Java 1.6 API for Queue says there is a method boolean offer(E e), where E is a parameterized type, and indeed, I have implemented that, as shown below.

Any help?

import java.util.ArrayDeque;
import java.util.Iterator;
import java.util.Queue;

public class MyBoundedQueue<ItemType> implements Queue
{
    private int _maxSize;
    private ArrayDeque<ItemType> _window;

    public MyBoundedQueue(int maxSize)
    {
        _maxSize = maxSize;
        _window = new ArrayDeque<ItemType>(_maxSize);
    }

    public boolean add(ItemType item)
    {
        if (_window.size() >=  _maxSize)
        {
            _window.removeFirst();
        }

        _window.addLast(item);
    }

    public ItemType element()
    {
        return _window.element();
    }

    public boolean offer(ItemType item)
    {
        add(item);
        return true;
    }

    public ItemType peek()
    {
        return _window.peek();
    }

    public ItemType poll()
    {
        return _window.poll();
    }

    public ItemType remove()
    {
        return _window.remove();
    }

    public void clear()
    {
        _window.clear();
    }

    public int size()
    {
        return _window.size();
    }

    public Iterator<ItemType> iterator()
    {
        return _window.iterator();
    }


}

Answer 1

You need to change it to:

public class MyBoundedQueue implements Queue<ItemType>

It’s telling you offer(Object) because without the Generic typing that’s what it would be. You also don’t need to specify a generic type for your class … you’re not using generic types anywhere.

If you wanted your class to use generics you’d want to do:

public class MyBoundedQueue<T> implements Queue<T> {
...

And everywhere you currently have ItemType you’d use T instead.