CollectionUtils.java
/*
* *********************************************************************************************************************
*
* TheseFoolishThings: Miscellaneous utilities
* http://tidalwave.it/projects/thesefoolishthings
*
* Copyright (C) 2009 - 2023 by Tidalwave s.a.s. (http://tidalwave.it)
*
* *********************************************************************************************************************
*
* 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.
*
* *********************************************************************************************************************
*
* git clone https://bitbucket.org/tidalwave/thesefoolishthings-src
* git clone https://github.com/tidalwave-it/thesefoolishthings-src
*
* *********************************************************************************************************************
*/
package it.tidalwave.util;
import javax.annotation.Nonnull;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Optional;
import lombok.AccessLevel;
import lombok.NoArgsConstructor;
import static java.util.Collections.emptyList;
/***********************************************************************************************************************
*
* This class contains a bunch of utility methods for manipulating lists.
*
* @author Fabrizio Giudici
* @since 3.2-ALPHA-13
* @it.tidalwave.javadoc.stable
*
**********************************************************************************************************************/
@NoArgsConstructor(access = AccessLevel.PRIVATE)
public final class CollectionUtils
{
/*******************************************************************************************************************
*
* Appends a list to an object. The resulting list is mutable.
*
* @param <T> the type of list items
* @param list the list
* @param object the list to append
* @return the list with the appended object
*
* @it.tidalwave.javadoc.stable
*
******************************************************************************************************************/
@Nonnull
public static <T> List<T> concat (@Nonnull final List<? extends T> list, @Nonnull final T object)
{
final List<T> result = new ArrayList<>(list);
result.add(object);
return result;
}
/*******************************************************************************************************************
*
* Returns a concatenation of the given {@link Collection}s.
*
* @param <T> the static type
* @param collections the input collections
* @return the concatenation
*
* @it.tidalwave.javadoc.stable
*
******************************************************************************************************************/
@Nonnull
public static <T> List<T> concat (@Nonnull final Collection<? extends T>... collections)
{
final List<T> result = new ArrayList<>();
for (final var collection : collections)
{
result.addAll(collection);
}
return result;
}
/*******************************************************************************************************************
*
* Reverses a list. The resulting list is mutable.
*
* @param <T> the type of list items
* @param list the list
* @return the reversed list
*
* @it.tidalwave.javadoc.stable
*
******************************************************************************************************************/
@Nonnull
public static <T> List<T> reversed (@Nonnull final List<? extends T> list)
{
final List<T> result = new ArrayList<>(list);
Collections.reverse(result);
return result;
}
/*******************************************************************************************************************
*
* Sorts a list. The resulting list is mutable.
*
* @param <T> the type of list items
* @param list the list
* @return the sorted list
* @since 3.2-ALPHA-13
*
* @it.tidalwave.javadoc.stable
*
******************************************************************************************************************/
@Nonnull
public static <T extends Comparable<? super T>> List<T> sorted (@Nonnull final List<? extends T> list)
{
final var result = new ArrayList<T>(list);
Collections.sort(result);
return result;
}
/*******************************************************************************************************************
*
* Sorts a list with a given {@link Comparator}. The resulting list is mutable.
*
* @param <T> the type of list items
* @param list the list
* @param comparator the comparator
* @return the sorted list
* @since 3.2-ALPHA-13
*
* @it.tidalwave.javadoc.stable
*
******************************************************************************************************************/
@Nonnull
public static <T> List<T> sorted (@Nonnull final List<? extends T> list,
@Nonnull final Comparator<? super T> comparator)
{
final var result = new ArrayList<T>(list);
result.sort(comparator);
return result;
}
/*******************************************************************************************************************
*
* Returns the (optional) first element of a list.
*
* @param <T> the type of list items
* @param list the list
* @return the first element
*
* @it.tidalwave.javadoc.stable
*
******************************************************************************************************************/
@Nonnull
public static <T> Optional<T> optionalHead (@Nonnull final List<? extends T> list)
{
return list.isEmpty() ? Optional.empty() : Optional.of(list.get(0));
}
/*******************************************************************************************************************
*
* Returns the first element of a list.
*
* @param <T> the type of list items
* @param list the list (cannot be empty)
* @return the first element
* @throws IllegalArgumentException if the list is empty
*
* @it.tidalwave.javadoc.stable
*
******************************************************************************************************************/
@Nonnull
public static <T> T head (@Nonnull final List<? extends T> list)
{
if (list.isEmpty())
{
throw new IllegalArgumentException("List is empty");
}
return list.get(0);
}
/*******************************************************************************************************************
*
* Returns the tail element of a list, that is a list without the first element. The tail of an empty list is an
* empty list. The resulting list is mutable.
*
* @param <T> the type of list items
* @param list the list
* @return the tail of the list
*
* @it.tidalwave.javadoc.stable
*
******************************************************************************************************************/
@Nonnull
public static <T> List<T> tail (@Nonnull final List<? extends T> list)
{
return new ArrayList<>(list.subList(1, list.size()));
}
/*******************************************************************************************************************
*
* Return a sublist of the original {@link List}, from the given {@code from} and {@code to} index (not included).
* If the {@code from} index is negative and/or the {@code to} index is lower than the {@code from} index or if an
* attempt is made to read before the start or past the end of the list, truncation silently occurs.
*
* @param <T> the static type
* @param list the original list
* @param from the first index (included)
* @param to the last index (excluded)
* @return the sublist
* @since 3.2-ALPHA-17
*
******************************************************************************************************************/
@Nonnull
public static <T> List<T> safeSubList (@Nonnull final List<? extends T> list, final int from, final int to)
{
final var safeFrom = Math.max(from, 0);
final var safeTo = Math.min(list.size(), to);
return (safeFrom >= safeTo) ? emptyList() : new ArrayList<>(list.subList(safeFrom, safeTo));
}
/*******************************************************************************************************************
*
* Splits a given {@link List} at a set of boundaries. Each boundary is the starting point of a sublist to be
* returned.
*
* @param <T> the static type
* @param list the original list
* @param boundaries the boundaries
* @return a list of sublists
* @since 3.2-ALPHA-17
*
******************************************************************************************************************/
@Nonnull
public static <T> List<List<T>> split (@Nonnull final List<? extends T> list, final int ... boundaries)
{
final var result = new ArrayList<List<T>>();
for (var i = 0; i < boundaries.length - 1; i++)
{
result.add(safeSubList(list, boundaries[i], boundaries[i + 1]));
}
return result;
}
}