/** * 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 com.leansoft.luxun.utils; import java.util.Iterator; import java.util.NoSuchElementException; /** * a template for object iterator * */ public abstract class IteratorTemplate<T> implements Iterator<T> { enum State { DONE, READY, NOT_READY, FAILED; } private State state = State.NOT_READY; private T nextItem = null; public T next() { if (!hasNext()) throw new NoSuchElementException(); state = State.NOT_READY; return nextItem; } public boolean hasNext() { switch (state) { case FAILED: throw new IllegalStateException("Iterator is in failed state"); case DONE: return false; case READY: return true; case NOT_READY: break; } return maybeComputeNext(); } protected abstract T makeNext(); private boolean maybeComputeNext() { state = State.FAILED; nextItem = makeNext(); if (state == State.DONE) return false; state = State.READY; return true; } public void remove() { throw new UnsupportedOperationException(); } protected void resetState() { state = State.NOT_READY; } protected T allDone() { state = State.DONE; return null; } }