package org.apache.lucene.util; import java.util.Iterator; import java.util.NoSuchElementException; /** * 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. */ /** * An {@link Iterator} implementation that filters elements with a boolean predicate. * @see #predicateFunction */ public abstract class FilterIterator<T> implements Iterator<T> { private final Iterator<T> iterator; private T next = null; private boolean nextIsSet = false; /** returns true, if this element should be returned by {@link #next()}. */ protected abstract boolean predicateFunction(T object); public FilterIterator(Iterator<T> baseIterator) { this.iterator = baseIterator; } public final boolean hasNext() { return nextIsSet || setNext(); } public final T next() { if (!hasNext()) { throw new NoSuchElementException(); } assert nextIsSet; try { return next; } finally { nextIsSet = false; next = null; } } public final void remove() { throw new UnsupportedOperationException(); } private boolean setNext() { while (iterator.hasNext()) { final T object = iterator.next(); if (predicateFunction(object)) { next = object; nextIsSet = true; return true; } } return false; } }