package com.carrotsearch.hppc;
import java.util.Iterator;
import java.util.NoSuchElementException;
Simplifies the implementation of iterators a bit. Modeled loosely after
Google Guava's API.
/**
* Simplifies the implementation of iterators a bit. Modeled loosely after
* Google Guava's API.
*/
public abstract class AbstractIterator<E> implements Iterator<E> {
private final static int NOT_CACHED = 0;
private final static int CACHED = 1;
private final static int AT_END = 2;
Current iterator state. /** Current iterator state. */
private int state = NOT_CACHED;
The next element to be returned from next()
if fetched. /**
* The next element to be returned from {@link #next()} if fetched.
*/
private E nextElement;
{@inheritDoc}
/**
* {@inheritDoc}
*/
@Override
public boolean hasNext() {
if (state == NOT_CACHED) {
state = CACHED;
nextElement = fetch();
}
return state == CACHED;
}
{@inheritDoc}
/**
* {@inheritDoc}
*/
@Override
public E next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
state = NOT_CACHED;
return nextElement;
}
Default implementation throws UnsupportedOperationException
. /**
* Default implementation throws {@link UnsupportedOperationException}.
*/
@Override
public void remove() {
throw new UnsupportedOperationException();
}
Fetch next element. The implementation must return done()
when all elements have been fetched. Returns: Returns the next value for the iterator or chain-calls done()
.
/**
* Fetch next element. The implementation must return {@link #done()} when all
* elements have been fetched.
*
* @return Returns the next value for the iterator or chain-calls {@link #done()}.
*/
protected abstract E fetch();
Call when done.
Returns: Returns a unique sentinel value to indicate end-of-iteration.
/**
* Call when done.
*
* @return Returns a unique sentinel value to indicate end-of-iteration.
*/
protected final E done() {
state = AT_END;
return null;
}
}