com.mchange.v1.util.ListUtils Maven / Gradle / Ivy
/*
* Distributed as part of mchange-commons-java 0.2.11
*
* Copyright (C) 2015 Machinery For Change, Inc.
*
* Author: Steve Waldman
*
* This library is free software; you can redistribute it and/or modify
* it under the terms of EITHER:
*
* 1) The GNU Lesser General Public License (LGPL), version 2.1, as
* published by the Free Software Foundation
*
* OR
*
* 2) The Eclipse Public License (EPL), version 1.0
*
* You may choose which license to accept if you wish to redistribute
* or modify this work. You may offer derivatives of this work
* under the license you have chosen, or you may provide the same
* choice of license which you have been offered here.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
*
* You should have received copies of both LGPL v2.1 and EPL v1.0
* along with this software; see the files LICENSE-EPL and LICENSE-LGPL.
* If not, the text of these licenses are currently available at
*
* LGPL v2.1: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html
* EPL v1.0: http://www.eclipse.org/org/documents/epl-v10.php
*
*/
package com.mchange.v1.util;
import java.util.*;
public final class ListUtils
{
public static List oneElementUnmodifiableList(final Object elem)
{
return new AbstractList()
{
public Iterator iterator()
{ return IteratorUtils.oneElementUnmodifiableIterator( elem ); }
public int size() { return 1; }
public boolean isEmpty()
{ return false; }
public boolean contains(Object o)
{ return o == elem; }
public Object get(int index)
{
if (index != 0)
throw new IndexOutOfBoundsException("One element list has no element index " +
index);
else
return elem;
}
};
}
//we could improve performance here by delegating to a method
//that didn't recheck size...
public static boolean equivalent(List a, List b)
{
if (a.size() != b.size())
return false;
else
{
Iterator ii = a.iterator();
Iterator jj = b.iterator();
return IteratorUtils.equivalent(ii, jj);
}
}
/**
* finds a hash value which takes into account
* the value of all elements, such that two sets
* for which equivalent(a, b) returns
* true will hashContents() to the same value
*/
public static int hashContents(List l)
{
int out = 0;
int count = 0;
for (Iterator ii = l.iterator(); ii.hasNext(); ++count)
{
Object o = ii.next();
if (o != null) out ^= (o.hashCode() ^ count);
}
return out;
}
}