Mega Code Archive
A combination of two collections into a collection
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/* DualCollection.java
{{IS_NOTE
Purpose:
Description:
History:
Sun Sep 2 21:29:38 2007, Created by tomyeh
}}IS_NOTE
Copyright (C) 2007 Potix Corporation. All Rights Reserved.
{{IS_RIGHT
This program is distributed under GPL Version 3.0 in the hope that
it will be useful, but WITHOUT ANY WARRANTY.
}}IS_RIGHT
*/
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.AbstractCollection;
/**
* A combination of two collections into a collection.
*
* @author tomyeh
* @since 3.0.0
*/
public class DualCollection extends AbstractCollection
implements java.io.Serializable {
private final Collection _first, _second;
/** Returns a collection by combining two collections.
* It checks whether any of them is null, or equals. And, returns
* the non-null one if another is null.
* If both null, it returns null.
*/
public static final
Collection combine(Collection first, Collection second) {
if (first == second) //we don't use equals to have better performance
return first;
if (first != null)
if (second != null)
return new DualCollection(first, second);
else
return first;
else
return second;
}
/** Constructor.
* It is better to use {@link #combine} instead of this method
* since it checks whether any of them is null or equals.
*/
public DualCollection(Collection first, Collection second) {
_first = first != null ? first: Collections.EMPTY_LIST;
_second = second != null ? second: Collections.EMPTY_LIST;
}
//Collection//
public int size() {
return _first.size() + _second.size();
}
public Iterator iterator() {
return new Iter();
}
private class Iter implements Iterator {
private Iterator _it;
private boolean _bSecond;
private Iter() {
_it = _first.iterator();
}
public boolean hasNext() {
return _it.hasNext() || (!_bSecond && !_second.isEmpty());
}
public Object next() {
if (!_bSecond && !_it.hasNext()) {
_it = _second.iterator();
_bSecond = true;
}
return _it.next();
}
public void remove() {
_it.remove();
}
}
}
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