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scorex package for Java SCORE
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package scorex.util;

import java.util.Collection;
import java.util.Iterator;

public abstract class AbstractCollection implements Collection {

    protected AbstractCollection() {
    }

    public abstract Iterator iterator();

    public abstract int size();

    public boolean isEmpty() {
        return size() == 0;
    }

    public boolean contains(Object o) {
        Iterator e = iterator();
        if (o==null) {
            while (e.hasNext())
                if (e.next()==null)
                    return true;
        } else {
            while (e.hasNext())
                if (o.equals(e.next()))
                    return true;
        }
        return false;
    }

    public Object[] toArray() {
        throw new UnsupportedOperationException();
    }

    public  T[] toArray(T[] a) {
        throw new UnsupportedOperationException();
    }

    public boolean add(E e) {
        throw new UnsupportedOperationException();
    }

    public boolean remove(Object o) {
        Iterator e = iterator();
        if (o==null) {
            while (e.hasNext()) {
                if (e.next()==null) {
                    e.remove();
                    return true;
                }
            }
        } else {
            while (e.hasNext()) {
                if (o.equals(e.next())) {
                    e.remove();
                    return true;
                }
            }
        }
        return false;
    }

    public boolean containsAll(Collection c) {
        Iterator e = c.iterator();
        while (e.hasNext())
            if (!contains(e.next()))
                return false;
        return true;
    }

    public boolean addAll(Collection c) {
        boolean modified = false;
        Iterator e = c.iterator();
        while (e.hasNext()) {
            if (add(e.next()))
                modified = true;
        }
        return modified;
    }

    public boolean removeAll(Collection c) {
        boolean modified = false;
        Iterator e = iterator();
        while (e.hasNext()) {
            if (c.contains(e.next())) {
                e.remove();
                modified = true;
            }
        }
        return modified;
    }

    public boolean retainAll(Collection c) {
        boolean modified = false;
        Iterator e = iterator();
        while (e.hasNext()) {
            if (!c.contains(e.next())) {
                e.remove();
                modified = true;
            }
        }
        return modified;
    }

    public String toString() {
        Iterator i = iterator();
        if (!i.hasNext())
            return "[]";

        StringBuilder sb = new StringBuilder();
        sb.append('[');
        for (;;) {
            E e = i.next();
            sb.append(e == this ? "(this Collection)" : e);
            if (!i.hasNext())
                return sb.append(']').toString();
            sb.append(", ");
        }
    }
}