content: /*
   * 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;
          }
      }
  
  }
  