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      1 /*
      2  * Copyright (C) 2007 The Guava Authors
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  * http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.google.common.base;
     18 
     19 import static com.google.common.base.Preconditions.checkState;
     20 
     21 import com.google.common.annotations.GwtCompatible;
     22 
     23 import java.util.Iterator;
     24 import java.util.NoSuchElementException;
     25 
     26 /**
     27  * Note this class is a copy of
     28  * {@link com.google.common.collect.AbstractIterator} (for dependency reasons).
     29  */
     30 @GwtCompatible
     31 abstract class AbstractIterator<T> implements Iterator<T> {
     32   private State state = State.NOT_READY;
     33 
     34   protected AbstractIterator() {}
     35 
     36   private enum State {
     37     READY, NOT_READY, DONE, FAILED,
     38   }
     39 
     40   private T next;
     41 
     42   protected abstract T computeNext();
     43 
     44   protected final T endOfData() {
     45     state = State.DONE;
     46     return null;
     47   }
     48 
     49   @Override
     50   public final boolean hasNext() {
     51     checkState(state != State.FAILED);
     52     switch (state) {
     53       case DONE:
     54         return false;
     55       case READY:
     56         return true;
     57       default:
     58     }
     59     return tryToComputeNext();
     60   }
     61 
     62   private boolean tryToComputeNext() {
     63     state = State.FAILED; // temporary pessimism
     64     next = computeNext();
     65     if (state != State.DONE) {
     66       state = State.READY;
     67       return true;
     68     }
     69     return false;
     70   }
     71 
     72   @Override
     73   public final T next() {
     74     if (!hasNext()) {
     75       throw new NoSuchElementException();
     76     }
     77     state = State.NOT_READY;
     78     return next;
     79   }
     80 
     81   @Override public final void remove() {
     82     throw new UnsupportedOperationException();
     83   }
     84 }
     85