In one of the projects I needed a simple Round Robin list, which would just return the next object in round robin fashion.
Even though it's trivial to come up with one, surprised to find out that I didn't find any hits when I searched for one.
This is what I came up with after half-hour. Use it as you wish. Download here.
package org.brsanthu.misc;
import java.util.ArrayList;
import java.util.Collection;
/**
* Simple extension to <code>ArrayList</code> with round robin functionality.
* <p>
* Just adds one method {@link #getNext()} which would return the next object
* in the list and the method starts over at first element after reaching the
* end of list.
* <p>
* This class it NOT designed for multi-threaded access. So necessary synchronization
* is required before accessing {@link #getNext()} method.
*
* @since Sep 24th 2007
* @author Santhosh Kumar
*/
public class RoundRobinList extends ArrayList {
private static final long serialVersionUID = 1L;
/**
* Last used index. Initially it would be -1, so that
* first element returned is 0th element of the list.
*/
private int lastIndex = -1;
/**
* Constructs a new round robin list with default capacity.
*/
public RoundRobinList() {
super();
}
/**
* Constructs a new round robin list and pre-populates with the
* objects found in given list.
* <p>
* For more information about usage of the c, see the <code>ArrayList</code> constructor
* page.
*
* @param c - collection of objects to be added by default to the new list.
*/
public RoundRobinList(Collection c) {
super(c);
}
/**
* Creates the new round robin list with specified capacity.
*
* @param initialCapacity - initial capacity.
*/
public RoundRobinList(int initialCapacity) {
super(initialCapacity);
}
/**
* Returns the next object in the list.
* <p>
* First invocation of this method after creating the list, always returns
* the 0th element. Starts over the 0th element after reaching the end of
* list.
* <p>
* If there are no objects in the list, returns <code>null</code>.
*
* @return - returns the next object in the list. <code>null</code> if list is
* empty.
*
*/
public Object getNext() {
if (isEmpty()) {
return null;
}
lastIndex++;
if (lastIndex >= size()) {
lastIndex = 0;
}
return get(lastIndex);
}
} |
| Java2html |
# posted by Santhosh @ 3:48 PM
