no.mnemonic.commons.utilities.collections.ListUtils Maven / Gradle / Ivy
package no.mnemonic.commons.utilities.collections;
import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;
public class ListUtils {
private ListUtils() {
}
/**
* Creates a list from its arguments.
*
* @param values Values to be added to the list.
* @param Type of value parameters.
* @return A list containing all values.
*/
@SafeVarargs
public static List list(T... values) {
if (values == null) return new ArrayList<>();
return new ArrayList<>(Arrays.asList(values));
}
/**
* Creates a list from an iterator.
*
* @param iterator An iterator which values are added to the list.
* @param Type of iterator values.
* @return A list containing all values supplied by the given iterator.
*/
public static List list(Iterator iterator) {
return list(iterator, v -> v);
}
/**
* Creates a list from another collection.
*
* @param collection A collection which values are added to the list.
* @param Type of collection values.
* @return A list containing all values contained in the given collection.
*/
public static List list(Collection collection) {
if (collection == null) return new ArrayList<>();
return new ArrayList<>(collection);
}
/**
* Creates a list from its arguments using a mapping function converting all values.
*
* @param mapping A mapping function applied to all values.
* @param values Values to be added to the list.
* @param Type of value parameters before conversion.
* @param Type of values in the returned list after conversion.
* @return A list containing all values converted using the mapping function.
*/
@SafeVarargs
public static List list(Function mapping, T... values) {
if (values == null) return new ArrayList<>();
return list(Arrays.asList(values), mapping);
}
/**
* Creates a list from an iterator using a mapping function converting all values.
*
* @param iterator An iterator which values are added to the list.
* @param mapping A mapping function applied to all values.
* @param Type of iterator values before conversion.
* @param Type of values in the returned list after conversion.
* @return A list containing all values supplied by the given iterator and converted using the mapping function.
*/
public static List list(Iterator iterator, Function mapping) {
if (mapping == null) throw new IllegalArgumentException("Mapping function not set!");
if (iterator == null) return new ArrayList<>();
List result = new ArrayList<>();
iterator.forEachRemaining(o -> result.add(mapping.apply(o)));
return result;
}
/**
* Creates a list from another collection using a mapping function converting all values.
*
* @param collection A collection which values are added to the list.
* @param mapping A mapping function applied to all values.
* @param Type of collection values before conversion.
* @param Type of values in the returned list after conversion.
* @return A list containing all values contained in the given collection and converted using the mapping function.
*/
public static List list(Collection collection, Function mapping) {
if (mapping == null) throw new IllegalArgumentException("Mapping function not set!");
if (collection == null) return new ArrayList<>();
return collection.stream().map(mapping).collect(Collectors.toList());
}
/**
* Adds an element to a list unless the element is null.
*
* A new list is created if the provided list is null.
*
* @param list List to which the element will be added.
* @param element Element to add.
* @param Type of elements.
* @return List including added element.
*/
public static List addToList(List list, T element) {
if (list == null) list = new ArrayList<>();
if (element == null) return list;
list.add(element);
return list;
}
/**
* Concatenates multiple lists into one new list.
*
* @param lists Multiple lists which will be concatenated.
* @param Type of list values.
* @return A list containing all values from the given lists.
*/
@SafeVarargs
public static List concatenate(List... lists) {
if (lists == null) return new ArrayList<>();
List result = new ArrayList<>();
for (List l : lists) {
if (l != null) result.addAll(l);
}
return result;
}
}