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/*******************************************************************************
* Copyright (c) 2009 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.common.utility.internal.iterables;
import java.util.Iterator;
import org.eclipse.jpt.common.utility.internal.StringTools;
import org.eclipse.jpt.common.utility.internal.iterators.ChainIterator;
/**
* A <code>ChainIterable</code> provides a pluggable {@link Iterable}
* that loops over a chain of arbitrarily linked objects. The chain
* should be null-terminated (i.e. a call to the {@link #nextLink(Object)}
* method should return <code>null</code> when it is passed the last
* link of the chain).
* To use, supply a starting link and supply a {@link ChainIterator.Linker} or
* subclass <code>ChainIterable</code> and override the
* {@link #nextLink(Object)} method.
* The starting link will be the first object returned by the iterable's iterator.
* If the starting link is <code>null</code>, the iterable will be empty.
* Note this iterable does not support <code>null</code> elements.
*
* @param <E> the type of elements returned by the iterable's iterator
*
* @see ChainIterator
*/
public class ChainIterable<E>
implements Iterable<E>
{
private final E startLink;
private final ChainIterator.Linker<E> linker;
/**
* Construct an iterable with the specified starting link
* and a default linker that calls back to the iterable.
* Use this constructor if you want to override the
* {@link #nextLink(Object)} method instead of building
* a {@link ChainIterator.Linker}.
*/
public ChainIterable(E startLink) {
super();
this.startLink = startLink;
this.linker = this.buildDefaultLinker();
}
/**
* Construct an iterator with the specified starting link
* and linker.
*/
public ChainIterable(E startLink, ChainIterator.Linker<E> linker) {
super();
this.startLink = startLink;
this.linker = linker;
}
protected ChainIterator.Linker<E> buildDefaultLinker() {
return new DefaultLinker();
}
public Iterator<E> iterator() {
return new ChainIterator<E>(this.startLink, this.linker);
}
/**
* Return the next link in the chain; null if there are no more links.
* <p>
* This method can be overridden by a subclass as an alternative to
* building a {@link ChainIterator.Linker}.
*/
protected E nextLink(@SuppressWarnings("unused") E currentLink) {
throw new RuntimeException("This method was not overridden."); //$NON-NLS-1$
}
@Override
public String toString() {
return StringTools.buildToStringFor(this, this.startLink);
}
//********** default linker **********
protected class DefaultLinker implements ChainIterator.Linker<E> {
public E nextLink(E currentLink) {
return ChainIterable.this.nextLink(currentLink);
}
}
}
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