// guts of AbstractCollection.java

package java.util;

public abstract class AbstractCollection<E> implements Collection<E> {

    protected AbstractCollection() { }

    // Query Operations
    public abstract Iterator<E> iterator();
    public abstract int size();

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

    public boolean contains(Object o) {
	Iterator<E> 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() {
	Object[] result = new Object[size()];
	Iterator<E> e = iterator();
	for (int i=0; e.hasNext(); i++)
	    result[i] = e.next();
	return result;
    }

    public <T> T[] toArray(T[] a) {
        int size = size();
        if (a.length < size)
            a = (T[])java.lang.reflect.Array
		.newInstance(a.getClass().getComponentType(), size);

        Iterator<E> it=iterator();
	Object[] result = a;
        for (int i=0; i<size; i++)
            result[i] = it.next();
        if (a.length > size)
	    a[size] = null;
        return a;
    }

    // Modification Operations

    public boolean add(E o) {  // subclasses should override
	throw new UnsupportedOperationException();
    }

    public boolean remove(Object o) {
	Iterator<E> 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;
    }

    // Bulk Operations

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

    public boolean addAll(Collection<? extends E> c) {
	boolean modified = false;
	Iterator<? extends E> 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> e = iterator();
	while (e.hasNext()) {
	    if (!c.contains(e.next())) {
		e.remove();
		modified = true;
	    }
	}
	return modified;
    }

    public void clear() {
	Iterator<E> e = iterator();
	while (e.hasNext()) {
	    e.next();
	    e.remove();
	}
    }

    //  String conversion

    public String toString() {
	StringBuffer buf = new StringBuffer();
	buf.append("[");

        Iterator<E> i = iterator();
        boolean hasNext = i.hasNext();
        while (hasNext) {
            E o = i.next();
            buf.append(o == this ? "(this Collection)" : String.valueOf(o));
            hasNext = i.hasNext();
            if (hasNext)
                buf.append(", ");
        }

	buf.append("]");
	return buf.toString();
    }

}