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/*
* 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.datastax.oss.driver.internal.core.util;
import com.datastax.oss.driver.shaded.guava.common.base.Preconditions;
import java.util.Iterator;
import java.util.NoSuchElementException;
import net.jcip.annotations.NotThreadSafe;
/**
* An iterator that knows in advance how many elements it will return, and maintains a counter as
* elements get returned.
*/
@NotThreadSafe
public abstract class CountingIterator implements Iterator {
protected int remaining;
public CountingIterator(int remaining) {
this.remaining = remaining;
}
public int remaining() {
return remaining;
}
/*
* The rest of this class was adapted from Guava's `AbstractIterator` (which we can't extend
* because its `next` method is final). Guava copyright notice follows:
*
* Copyright (C) 2007 The Guava Authors
*
* Licensed 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.
*/
private enum State {
READY,
NOT_READY,
DONE,
FAILED,
}
private State state = State.NOT_READY;
private ElementT next;
protected abstract ElementT computeNext();
protected final ElementT endOfData() {
state = State.DONE;
return null;
}
@Override
public final boolean hasNext() {
Preconditions.checkState(state != State.FAILED);
switch (state) {
case DONE:
return false;
case READY:
return true;
default:
}
return tryToComputeNext();
}
private boolean tryToComputeNext() {
state = State.FAILED; // temporary pessimism
next = computeNext();
if (state != State.DONE) {
state = State.READY;
return true;
}
return false;
}
@Override
public final ElementT next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
state = State.NOT_READY;
ElementT result = next;
next = null;
// Added to original Guava code: decrement counter when we return an element
remaining -= 1;
return result;
}
public final ElementT peek() {
if (!hasNext()) {
throw new NoSuchElementException();
}
return next;
}
}