/*******************************************************************************
* Copyright (c) 2002 - 2006 IBM Corporation.
* 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:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package com.ibm.wala.util.collections;
import java.util.Iterator;
/**
* A utility to efficiently compose an iterator and a singleton
*/
public class IteratorPlusOne<T> implements Iterator<T> {
public static <T> IteratorPlusOne<T> make(Iterator<? extends T> it, T xtra) {
if (it == null) {
throw new IllegalArgumentException("null it");
}
return new IteratorPlusOne<T>(it, xtra);
}
private final Iterator<? extends T> it;
// the following field will be nulled out after visiting xtra.
private T xtra;
private IteratorPlusOne(Iterator<? extends T> it, T xtra) {
this.it = it;
this.xtra = xtra;
}
@Override
public boolean hasNext() {
return it.hasNext() || (xtra != null);
}
@Override
public T next() {
if (it.hasNext()) {
return it.next();
} else {
T result = xtra;
xtra = null;
return result;
}
}
@Override
public void remove() throws UnsupportedOperationException {
throw new UnsupportedOperationException();
}
}