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/*******************************************************************************
* Copyright (c) 2005, 2008 Oracle. All rights reserved.
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v1.0, which accompanies this distribution
* and is available at http://www.eclipse.org/legal/epl-v10.html.
*
* Contributors:
* Oracle - initial API and implementation
******************************************************************************/
package org.eclipse.jpt.utility.internal.iterators;
import java.util.Collection;
import java.util.Iterator;
import org.eclipse.jpt.utility.internal.StringTools;
/**
* A <code>CloneIterator</code> iterates over a copy of a collection,
* allowing for concurrent access to the original collection.
* <p>
* The original collection passed to the <code>CloneIterator</code>'s
* constructor should be synchronized; otherwise you run the risk of
* a corrupted collection.
* <p>
* By default, a <code>CloneIterator</code> does not support the
* <code>#remove()</code> operation; this is because it does not have
* access to the original collection. But if the <code>CloneIterator</code>
* is supplied with an <code>Mutator</code> it will delegate the
* <code>#remove()</code> operation to the <code>Mutator</code>.
* Alternatively, a subclass can override the <code>#remove(Object)</code>
* method.
*/
public class CloneIterator<E>
implements Iterator<E>
{
private final Iterator<Object> nestedIterator;
private E current;
private final Mutator<E> mutator;
private boolean removeAllowed;
// ********** constructors **********
/**
* Construct an iterator on a copy of the specified collection.
* The <code>#remove()</code> method will not be supported,
* unless a subclass overrides the <code>#remove(Object)</code>.
*/
public CloneIterator(Collection<? extends E> c) {
this(c, Mutator.ReadOnly.<E>instance());
}
/**
* Construct an iterator on a copy of the specified collection.
* Use the specified mutator to remove objects from the
* original collection.
*/
public CloneIterator(Collection<? extends E> c, Mutator<E> mutator) {
super();
this.nestedIterator = new ArrayIterator<Object>(c.toArray());
this.current = null;
this.mutator = mutator;
this.removeAllowed = false;
}
// ********** Iterator implementation **********
public boolean hasNext() {
return this.nestedIterator.hasNext();
}
public E next() {
this.current = this.nestedNext();
this.removeAllowed = true;
return this.current;
}
public void remove() {
if ( ! this.removeAllowed) {
throw new IllegalStateException();
}
this.remove(this.current);
this.removeAllowed = false;
}
// ********** internal methods **********
/**
* The collection passed in during construction held Es,
* so this cast is not a problem. We need this cast because
* all the elements of the original collection were copied into
* an object array (Object[]).
*/
@SuppressWarnings("unchecked")
protected E nestedNext() {
return (E) this.nestedIterator.next();
}
/**
* Remove the specified element from the original collection.
* <p>
* This method can be overridden by a subclass as an
* alternative to building an <code>Mutator</code>.
*/
protected void remove(E e) {
this.mutator.remove(e);
}
@Override
public String toString() {
return StringTools.buildToStringFor(this);
}
//********** member interface **********
/**
* Used by <code>CloneIterator</code> to remove
* elements from the original collection; since the iterator
* does not have direct access to the original collection.
*/
public interface Mutator<T> {
/**
* Remove the specified object from the original collection.
*/
void remove(T current);
final class ReadOnly<S> implements Mutator<S> {
@SuppressWarnings("unchecked")
public static final Mutator INSTANCE = new ReadOnly();
@SuppressWarnings("unchecked")
public static <R> Mutator<R> instance() {
return INSTANCE;
}
// ensure single instance
private ReadOnly() {
super();
}
// remove is not supported
public void remove(Object current) {
throw new UnsupportedOperationException();
}
@Override
public String toString() {
return "CloneIterator.Mutator.ReadOnly";
}
}
}
}
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