| /* |
| * 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.kafka.common.utils; |
| |
| import java.util.Iterator; |
| import java.util.NoSuchElementException; |
| |
| /** |
| * A base class that simplifies implementing an iterator |
| * @param <T> The type of thing we are iterating over |
| */ |
| public abstract class AbstractIterator<T> implements Iterator<T> { |
| |
| private enum State { |
| READY, NOT_READY, DONE, FAILED |
| } |
| |
| private State state = State.NOT_READY; |
| private T next; |
| |
| @Override |
| public boolean hasNext() { |
| switch (state) { |
| case FAILED: |
| throw new IllegalStateException("Iterator is in failed state"); |
| case DONE: |
| return false; |
| case READY: |
| return true; |
| default: |
| return maybeComputeNext(); |
| } |
| } |
| |
| @Override |
| public T next() { |
| if (!hasNext()) |
| throw new NoSuchElementException(); |
| state = State.NOT_READY; |
| if (next == null) |
| throw new IllegalStateException("Expected item but none found."); |
| return next; |
| } |
| |
| @Override |
| public void remove() { |
| throw new UnsupportedOperationException("Removal not supported"); |
| } |
| |
| public T peek() { |
| if (!hasNext()) |
| throw new NoSuchElementException(); |
| return next; |
| } |
| |
| protected T allDone() { |
| state = State.DONE; |
| return null; |
| } |
| |
| protected abstract T makeNext(); |
| |
| private Boolean maybeComputeNext() { |
| state = State.FAILED; |
| next = makeNext(); |
| if (state == State.DONE) { |
| return false; |
| } else { |
| state = State.READY; |
| return true; |
| } |
| } |
| |
| } |