org.semanticweb.elk.util.collections.FList Maven / Gradle / Ivy
package org.semanticweb.elk.util.collections;
/*
* #%L
* ELK Utilities Collections
* $Id:$
* $HeadURL:$
* %%
* Copyright (C) 2011 - 2015 Department of Computer Science, University of Oxford
* %%
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
* #L%
*/
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* A simple interface for lists as used in functional programming;
*
*
* @author "Yevgeny Kazakov"
*
* @param
* the elements contained in the list
*/
public interface FList extends Iterable {
/**
* @return the first element in the list; it cannot be {@code null}
*/
E getHead();
/**
* @return the remaining elements of this {@link FList} except for the first
* one, or {@code null} if there are no such elements
*/
FList getTail();
public static class FListIterator implements Iterator {
private FList list_;
public FListIterator(FList list) {
this.list_ = list;
}
@Override
public boolean hasNext() {
return list_ != null;
}
@Override
public E next() {
if (list_ == null)
throw new NoSuchElementException();
E result = list_.getHead();
list_ = list_.getTail();
return result;
}
@Override
public void remove() {
throw new UnsupportedOperationException(
"The list cannot be modified!");
}
}
public static class Equality {
public static boolean equals(FList first, Object second) {
if (second instanceof FList) {
return equals(first, (FList) second);
}
// else
return false;
}
private static boolean equals(FList first, FList second) {
// implementation without recursive call
for (;;) {
if (first == second) {
return true;
}
// else
if (first == null || second == null) {
return false;
}
// else
if (!first.getHead().equals(second.getHead()))
return false;
// else
first = first.getTail();
second = second.getTail();
}
}
}
public static class Hash {
public static int hashCode(FList list) {
// compute has code like for a list
int result = 0;
for (;;) {
if (list == null)
return result;
// else
result = 31 * list.getHead().hashCode();
list = list.getTail();
}
}
}
}