Mega Code Archive
Implements a rolling list
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/*
* Copyright (c) 2006-2008 Chris Smith, Shane Mc Cormack, Gregory Holmes
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
//package com.dmdirc.util;
import java.util.ArrayList;
import java.util.List;
/**
* Implements a "rolling list". A rolling list has a maximum capacity, and
* removes the oldest elements from the list to maintain this capacity.
*
* @param <T> The type if items that this list contains
* @author chris
*/
public class RollingList<T> {
/** The items in this rolling list. */
private final List<T> items = new ArrayList<T>();
/** The maximum capacity of this list. */
private final int capacity;
/** This list's position pointer. */
private int position = 0;
/** Whether or not to add a fake empty item to the end of this list. */
private boolean addEmpty;
/** The "empty" item to be added. */
private T empty;
/**
* Creates a new RollingList of the specified capacity.
*
* @param capacity The capacity of this list.
*/
public RollingList(final int capacity) {
this.capacity = capacity;
this.addEmpty = false;
}
/**
* Creates a new RollingList of the specified capacity, with the specified
* "empty" element appended to the end.
*
* @param capacity The capacity of this list.
* @param empty The "empty" element to be added
*/
public RollingList(final int capacity, final T empty) {
this.capacity = capacity;
this.addEmpty = true;
this.empty = empty;
}
/**
* Removes the specified element from this list.
*
* @param o The object to be removed from the list.
* @return True if the list contained the specified element, false otherwise.
*/
public boolean remove(final Object o) {
return items.remove(o);
}
/**
* Determines if this list is currently empty.
*
* @return True if the list is empty, false otherwise.
*/
public boolean isEmpty() {
return items.isEmpty();
}
/**
* Retrieves the item at the specified index in this list.
*
* @param index The index to look up
* @return The item at the specified index
*/
public T get(final int index) {
return items.get(index);
}
/**
* Determines if this list contains the specified object.
*
* @param o The object to be checked
* @return True if this list contains the item, false otherwise.
*/
public boolean contains(final Object o) {
return items.contains(o);
}
/**
* Clears all items from this list.
*/
public void clear() {
items.clear();
}
/**
* Adds the specified item to this list. If the list has reached its
* maximum capacity, this method will remove elements from the start of the
* list until there is sufficient room for the new element.
*
* @param e The element to be added to the list.
* @return True
*/
public boolean add(T e) {
while (items.size() > capacity - 1) {
items.remove(0);
position--;
}
return items.add(e);
}
/**
* Retrieves the current position within the list.
*
* @return This list's positional pointer
*/
public int getPosition() {
return position;
}
/**
* Sets the positional pointer of this list.
*
* @param position The new position
*/
public void setPosition(int position) {
this.position = position;
}
/**
* Determines if there is an element after the positional pointer of the list.
*
* @return True if there is an element, false otherwise.
*/
public boolean hasNext() {
return (items.size() > position + 1) || ((items.size() > position) && addEmpty);
}
/**
* Retrieves the element after the positional pointer of the list.
*
* @return The next element in the list
*/
public T getNext() {
if (items.size() > position + 1 || !addEmpty) {
return get(++position);
} else {
position++;
return empty;
}
}
/**
* Determines if there is an element befpre the positional pointer of the list.
*
* @return True if there is an element, false otherwise.
*/
public boolean hasPrevious() {
return 0 < position;
}
/**
* Retrieves the element before the positional pointer of the list.
*
* @return The previous element in the list
*/
public T getPrevious() {
return get(--position);
}
/**
* Sets the positional pointer of this list to the end.
*/
public void seekToEnd() {
position = items.size();
}
/**
* Sets the positional pointer of this list to the start.
*/
public void seekToStart() {
position = 0;
}
/**
* Retrieves a list of items that this rolling list contains.
*
* @return A list of items in this rolling list.
*/
public List<T> getList() {
return new ArrayList<T>(items);
}
}
/*
import org.junit.Test;
import static org.junit.Assert.*;
public class WeakListTest extends junit.framework.TestCase {
@Test
public void testBasics() {
final WeakList<String> test = new WeakList<String>();
assertTrue(test.isEmpty());
test.add("abcdef");
test.add("123");
assertEquals(2, test.size());
assertTrue(test.get(0).equals("abcdef"));
assertTrue(test.contains("123"));
assertFalse(test.isEmpty());
test.remove("abcdef");
assertFalse(test.contains("abcdef"));
test.remove("123");
assertTrue(test.isEmpty());
}
}
*/
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