org.apache.jackrabbit.commons.iterator.AbstractLazyIterator Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jackrabbit.commons.iterator;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* {@code AbstractLazyIterator} provides basic iteration methods for a lazy loading iterator that does not support
* remove. Implementing classes only need to implement the {@link #getNext()} method which must return the next item
* in the iteration or {@code null} if the iteration as reached its end.
*/
public abstract class AbstractLazyIterator implements Iterator {
private boolean fetchNext = true;
private T next;
protected AbstractLazyIterator() {
}
@Override
public boolean hasNext() {
if (fetchNext) {
next = getNext();
fetchNext = false;
}
return next != null;
}
@Override
public T next() {
if (fetchNext) {
next = getNext();
} else {
fetchNext = true;
}
if (next == null) {
throw new NoSuchElementException();
}
return next;
}
/**
* Returns the next element of this iteration or {@code null} if the iteration has finished.
* @return the next element.
*/
abstract protected T getNext();
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}