//$Id: JoinedIterator.java 3973 2004-06-28 23:58:08Z epbernard $
package org.hibernate.util;
import java.util.Iterator;
import java.util.List;
/**
* An JoinedIterator is an Iterator that wraps a number of Iterators.
*
* This class makes multiple iterators look like one to the caller.
* When any method from the Iterator interface is called, the JoinedIterator
* will delegate to a single underlying Iterator. The JoinedIterator will
* invoke the Iterators in sequence until all Iterators are exhausted.
*
*/
public class JoinedIterator implements Iterator {
private static final Iterator[] ITERATORS = {};
// wrapped iterators
private Iterator[] iterators;
// index of current iterator in the wrapped iterators array
private int currentIteratorIndex;
// the current iterator
private Iterator currentIterator;
// the last used iterator
private Iterator lastUsedIterator;
public JoinedIterator(List iterators) {
this( (Iterator[]) iterators.toArray(ITERATORS) );
}
public JoinedIterator(Iterator[] iterators) {
if( iterators==null )
throw new NullPointerException("Unexpected NULL iterators argument");
this.iterators = iterators;
}
public JoinedIterator(Iterator first, Iterator second) {
this( new Iterator[] { first, second } );
}
public boolean hasNext() {
updateCurrentIterator();
return currentIterator.hasNext();
}
public Object next() {
updateCurrentIterator();
return currentIterator.next();
}
public void remove() {
updateCurrentIterator();
lastUsedIterator.remove();
}
// call this before any Iterator method to make sure that the current Iterator
// is not exhausted
protected void updateCurrentIterator() {
if (currentIterator == null) {
if( iterators.length==0 ) {
currentIterator = EmptyIterator.INSTANCE;
}
else {
currentIterator = iterators[0];
}
// set last used iterator here, in case the user calls remove
// before calling hasNext() or next() (although they shouldn't)
lastUsedIterator = currentIterator;
}
while (! currentIterator.hasNext() && currentIteratorIndex < iterators.length - 1) {
currentIteratorIndex++;
currentIterator = iterators[currentIteratorIndex];
}
}
}
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