Iterables.java
/*
** Module : Iterables.java
** Abstract : Helper methods which make convenient use of Iterable interface
** and foreach loops.
**
** Copyright (c) 2010-2019, Golden Code Development Corporation.
**
** -#- -I- --Date-- --JPRM-- ----------------Description-----------------
** 001 SIY 20100804 @ Created initial version
** 002 SIY 20110112 Minor cleanups.
** 003 HC 20191211 Added reverseFrom and directFrom overloads.
*/
/*
** This program is free software: you can redistribute it and/or modify
** it under the terms of the GNU Affero General Public License as
** published by the Free Software Foundation, either version 3 of the
** License, or (at your option) any later version.
**
** This program 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. See the
** GNU Affero General Public License for more details.
**
** You may find a copy of the GNU Affero GPL version 3 at the following
** location: https://www.gnu.org/licenses/agpl-3.0.en.html
**
** Additional terms under GNU Affero GPL version 3 section 7:
**
** Under Section 7 of the GNU Affero GPL version 3, the following additional
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**
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*/
package com.goldencode.p2j.util;
import java.util.*;
/**
* Set of helper methods for iterables.
*/
public class Iterables
{
/**
* Static factory method which returns reverse iterable for a given list.
*
* @param <T>
* List item type.
* @param list
* List.
*
* @return Instance of {@link Iterable} which performs iteration through
* elements in reverse order.
*/
public static <T> Iterable<T> reverse(final List<T> list)
{
return new RevIterable<T>(list.listIterator(list.size()));
}
/**
* Create new reverse iterable which will traverse list starting from
* given element.
*
* @param <T>
* List item type.
* @param list
* List.
* @param elem
* Initial element from which iteration will be started.
* Note that the element itself will not be returned.
*
* @return Instance of {@link Iterable} which performs iteration through
* elements in reverse order.
*/
public static <T> Iterable<T> reverseFrom(List<T> list, T elem)
{
return reverseFrom(list, elem, false);
}
/**
* Create new reverse iterable which will traverse list starting from
* given element.
*
* @param <T>
* List item type.
* @param list
* List.
* @param elem
* Initial element from which iteration will be started.
* @param inclusive
* When {@code true} the iterator will also include the initial element.
*
* @return Instance of {@link Iterable} which performs iteration through
* elements in reverse order.
*/
public static <T> Iterable<T> reverseFrom(List<T> list, T elem, boolean inclusive)
{
int idx = list.indexOf(elem);
if (idx < 0)
return null;
if (inclusive)
{
idx++;
}
return new RevIterable<T>(list.listIterator(idx));
}
/**
* Return iterable which traverses list in direct order starting from given
* element.
*
* @param <T>
* List item type.
* @param list
* List.
* @param elem
* Initial element from which iteration will be started.
* Note that the element itself will not be returned.
*
* @return Instance of {@link Iterable} which performs iteration through
* elements in direct order.
*/
public static <T> Iterable<T> directFrom(final List<T> list, T elem)
{
return directFrom(list, elem, false);
}
/**
* Return iterable which traverses list in direct order starting from given
* element.
*
* @param <T>
* List item type.
* @param list
* List.
* @param elem
* Initial element from which iteration will be started.
* @param inclusive
* When {@code true} the iterator will also include the initial element.
*
* @return Instance of {@link Iterable} which performs iteration through
* elements in direct order.
*/
public static <T> Iterable<T> directFrom(final List<T> list, T elem, boolean inclusive)
{
final int idx = list.indexOf(elem);
if (idx < 0)
return null;
final ListIterator<T> iter = list.listIterator(idx);
if (!inclusive && iter.hasNext())
iter.next();
return new Iterable<T>()
{
/**
* @see java.lang.Iterable#iterator()
*/
@Override
public Iterator<T> iterator()
{
return iter;
}
};
}
/**
* Reverse iterable implementation.
*
* @param <T>
*/
private static class RevIterable<T>
implements Iterable<T>
{
/**
* Underlying iterator.
*/
private final ListIterator<T> iter;
/**
* Constructor.
*
* @param iter
*/
RevIterable(ListIterator<T> iter)
{
this.iter = iter;
}
/**
* @see java.lang.Iterable#iterator()
*/
@Override
public Iterator<T> iterator()
{
return new Iterator<T>()
{
/**
* @see java.util.Iterator#hasNext()
*/
@Override
public boolean hasNext()
{
return iter.hasPrevious();
}
/**
* @see java.util.Iterator#next()
*/
@Override
public T next()
{
return iter.previous();
}
/**
* @see java.util.Iterator#remove()
*/
@Override
public void remove()
{
throw new UnsupportedOperationException();
}
};
}
}
}