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Kiwi is a utility library. We really like Google's Guava, and also use Apache Commons.
But if they don't have something we need, and we think it is useful, this is where we put it.
package org.kiwiproject.collect;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static java.util.Objects.isNull;
import static java.util.Objects.nonNull;
import lombok.experimental.UtilityClass;
import java.lang.reflect.Array;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Optional;
import java.util.stream.IntStream;
/**
* Utility methods for working with Array instances.
*/
@UtilityClass
public class KiwiArrays {
/**
* Checks whether the specified array is null or empty.
*
* @param items the array
* @param the type of items in the array
* @return {@code true} if array is null or empty; {@code false} otherwise
*/
public static boolean isNullOrEmpty(T[] items) {
return items == null || items.length == 0;
}
/**
* Checks whether the specified array is neither null nor empty.
*
* @param items the array
* @param the type of items in the array
* @return {@code true} if array is NOT null or empty; {@code false} otherwise
*/
public static boolean isNotNullOrEmpty(T[] items) {
return !isNullOrEmpty(items);
}
/**
* Checks whether the specified array is non-null and has only one item.
*
* @param items the array
* @param the type of items in the array
* @return {@code true} if array is non-null and has exactly one item; {@code false} otherwise
*/
public static boolean hasOneElement(T[] items) {
return nonNull(items) && items.length == 1;
}
/**
* Given an array, sort it according to the natural order, returning a new list.
*
* @param items the array
* @param arrayType the type of the items in the array. Needed to ensure the new array is not {@code Object[]}
* @param the type of items in the array
* @return a new sorted array
*/
@SuppressWarnings("unchecked")
public static T[] sorted(T[] items, Class arrayType) {
checkNonNullInputArray(items);
return Arrays.stream(items)
.sorted()
.toArray(size -> (T[]) Array.newInstance(arrayType, size));
}
/**
* Given an array, sort it according to the provided {@link Comparator} returning a new array.
*
* @param items the array
* @param comparator a Comparator to be used to compare stream elements
* @param arrayType the type of the items in the array. Needed to ensure the new array is not {@code Object[]}
* @param the type of items in the array
* @return a new sorted array
*/
@SuppressWarnings("unchecked")
public static T[] sorted(T[] items, Comparator comparator, Class arrayType) {
checkNonNullInputArray(items);
checkNotNull(comparator, "Comparator cannot be null");
return Arrays.stream(items)
.sorted(comparator)
.toArray(size -> (T[]) Array.newInstance(arrayType, size));
}
/**
* Return the first element in the specified array of items.
*
* @param items the array
* @param the type of items in the array
* @return the first item in items
* @throws IllegalArgumentException if the array does not contain at least one item
* @throws NullPointerException if the array is null
*/
public static T first(T[] items) {
return nth(items, 1);
}
/**
* Returns an {@link Optional} containing the first element in specified array of items, or an empty optional
* if the array is null or empty.
*
* @param items the array
* @param the type of items in the array
* @return Optional containing first element if exists, otherwise Optional.empty()
*/
public static Optional firstIfPresent(T[] items) {
return isNotNullOrEmpty(items) ? Optional.of(first(items)) : Optional.empty();
}
/**
* Return the second element in the specified array of items.
*
* @param items the array
* @param the type of items in the array
* @return the second item in items
* @throws IllegalArgumentException if the array does not contain at least two items
* @throws NullPointerException if the array is null
*/
public static T second(T[] items) {
return nth(items, 2);
}
/**
* Return the third element in the specified array of items.
*
* @param items the array
* @param the type of items in the array
* @return the third item in items
* @throws IllegalArgumentException if the array does not contain at least three items
* @throws NullPointerException if the array is null
*/
public static T third(T[] items) {
return nth(items, 3);
}
/**
* Return the fourth element in the specified array of items.
*
* @param items the array
* @param the type of items in the array
* @return the fourth item in items
* @throws IllegalArgumentException if the array does not contain at least four items
* @throws NullPointerException if the array is null
*/
public static T fourth(T[] items) {
return nth(items, 4);
}
/**
* Return the fifth element in the specified array of items.
*
* @param items the array
* @param the type of items in the array
* @return the fifth item in items
* @throws IllegalArgumentException if the array does not contain at least five items
* @throws NullPointerException if the array is null
*/
public static T fifth(T[] items) {
return nth(items, 5);
}
/**
* Returns the penultimate (second to last) element in the specified array.
*
* @param items the array
* @param the type of items in the array
* @return the penultimate item in items
* @throws IllegalArgumentException if the array does not contain at least two items
* @throws NullPointerException if the array is null
* @see #secondToLast(Object[])
*/
public static T penultimate(T[] items) {
checkMinimumSize(items, 2);
return nth(items, items.length - 1);
}
/**
* Synonym for {@link #penultimate(Object[])}.
*
* @param items the array
* @param the type of items in the array
* @return the penultimate item in items
* @throws IllegalArgumentException if the array does not contain at least two items
* @throws NullPointerException if the array is null
* @see #penultimate(Object[])
*/
public static T secondToLast(T[] items) {
return penultimate(items);
}
/**
* Returns the last element in the specified array of items.
*
* @param items the array
* @param the type of items in the array
* @return the last item in the list
* @throws IllegalArgumentException if the array does not contain at least one item
* @throws NullPointerException if the array is null
*/
public static T last(T[] items) {
return nth(items, items.length);
}
/**
* Returns an {@link Optional} containing the last element in specified array of items, or an empty optional
* if the array is null or empty.
*
* @param items the array
* @param the type of items in the array
* @return Optional containing last element if exists, otherwise Optional.empty()
*/
public static Optional lastIfPresent(T[] items) {
return isNotNullOrEmpty(items) ? Optional.of(last(items)) : Optional.empty();
}
/**
* Return the nth element in the specified array of items, starting at one for the first element, two for the
* second, etc.
*
* @param items the array
* @param number the number of the element to retrieve, starting at one (not zero)
* @param the type of items in the array
* @return the nth item in items
* @throws IllegalArgumentException if the array does not contain at least number items
* @throws NullPointerException if the array is null
*/
public static T nth(T[] items, int number) {
checkMinimumSize(items, number);
return items[number - 1];
}
/**
* Returns a array of the collection elements with duplicates stripped out.
*
* @param collection the collection of values
* @param arrayType the type of the items in the array. Needed to ensure the new array is not {@code Object[]}
* @param the type of items in the collection
* @return a new array with only unique elements
* @throws IllegalArgumentException if the collection is null
*/
public static T[] distinct(T[] collection, Class arrayType) {
checkArgument(nonNull(collection), "collection can not be null");
return distinctOrNull(collection, arrayType);
}
/**
* Returns a array of the collection elements with duplicates stripped out or `null` if a null value is passed in.
*
* @param collection the collection of values
* @param arrayType the type of the items in the array. Needed to ensure the new array is not {@code Object[]}
* @param the type of items in the collection
* @return a new array with only unique elements or null.
*/
@SuppressWarnings({"unchecked", "java:S1168"}) //Ignoring Sonar warning to return empty array since this method's name says it will return null
public static T[] distinctOrNull(T[] collection, Class arrayType) {
if (isNull(collection)) {
return null;
}
return Arrays.stream(collection)
.distinct()
.toArray(val -> (T[]) Array.newInstance(arrayType, val));
}
/**
* Returns a new array with the same elements and the same size as the original, however the initial position in the array
* is now the element specified by the "startOffset" and the array wraps around through the contents to end with "startOffset" - 1
*
* @param input the original array
* @param startOffset the desired offset to start the new array
* @param arrayType the type of the items in the array. Needed to ensure the new array is not {@code Object[]}
* @param the type of the items in the array
* @return a new array starting at the desired offset
*/
@SuppressWarnings("unchecked")
public static T[] newArrayStartingAtCircularOffset(T[] input, long startOffset, Class arrayType) {
var size = input.length;
return IntStream.range(0, size)
.mapToObj(i -> input[(int) (startOffset + i) % size])
.toArray(val -> (T[]) Array.newInstance(arrayType, val));
}
/**
* Returns a new array containing the portion of the given array excluding the first element.
*
* @param items the array
* @param the type of the items in the array
* @return a new array containing the given array excluding the first item
* @throws NullPointerException if the array is null
*/
public static T[] subArrayExcludingFirst(T[] items) {
checkNonNullInputArray(items);
if (items.length == 0) {
return zeroSubArray(items);
}
return Arrays.copyOfRange(items, 1, items.length);
}
/**
* Returns a new array containing the portion of the given array excluding the last element.
*
* @param items the array
* @param the type of the items in the array
* @return a new array containing the given array excluding the last item
* @throws NullPointerException if the array is null
*/
public static T[] subArrayExcludingLast(T[] items) {
checkNonNullInputArray(items);
if (items.length == 0) {
return zeroSubArray(items);
}
return Arrays.copyOfRange(items, 0, items.length-1);
}
private static T[] zeroSubArray(T[] items) {
return Arrays.copyOf(items, 0);
}
/**
* Returns a new array containing the portion of the given array starting at the given logical element number, where the
* numbers start at one, until and including the last element in the array. This is useful if something is using
* one-based element numbers for some reason. Use {@link #subArrayFromIndex(Object[], int)} if you want to use zero-based
* list indices.
*
* @param items the array
* @param number the number of the element to start the subarray, starting at one (not zero)
* @param the type of items in the array
* @return a new array containing the given array, starting at the given one-based number
* @throws NullPointerException if the array is null
* @throws IllegalArgumentException if the given number is negative or is higher than the size of the array
*/
public static T[] subArrayFrom(T[] items, int number) {
checkMinimumSize(items, number);
return Arrays.copyOfRange(items, number - 1, items.length);
}
/**
* Returns a new array containing the portion of the given array starting at the given index, until and including the last
* element in the array.
*
* @param items the array
* @param index the index in the array to start the subarray, zero-based like normal Array accessors
* @param the type of items in the array
* @return a new array containing the given array, starting at the given zero-based index
* @throws NullPointerException if the array is null
* @throws IllegalArgumentException if the given index is negative or is higher than the last index in the array
*/
public static T[] subArrayFromIndex(T[] items, int index) {
checkMinimumSize(items, index + 1);
return Arrays.copyOfRange(items, index, items.length);
}
/**
* Returns a new array containing the "first N" elements of the input array.
*
* If the given number is larger than the size of the array, the entire array is returned, rather than throw
* an exception. In this case, the input array is returned directly, i.e. {@code return items}.
*
* @param items the array
* @param number the number of items wanted from the start of the array
* @param the type of items in the array
* @return a new array containing the given array containing the last {@code number} elements
*/
public static T[] firstN(T[] items, int number) {
checkNonNullInputArray(items);
checkMinSizeIsPositive(number);
if (number > items.length) {
return items;
}
return Arrays.copyOfRange(items, 0, number);
}
/**
* Returns a new array containing the "last N" elements of the input array.
*
* If the given number is larger than the size of the array, the entire array is returned, rather than throw
* an exception. In this case, the input array is returned directly, i.e. {@code return items}.
*
* @param items the array
* @param number the number of items wanted from the end of the array
* @param the type of items in the array
* @return a new array containing the given array containing the first {@code number} elements
*/
public static T[] lastN(T[] items, int number) {
checkNonNullInputArray(items);
checkMinSizeIsPositive(number);
if (number > items.length) {
return items;
}
var startIndex = items.length - number;
return Arrays.copyOfRange(items, startIndex, items.length);
}
/**
* Checks that the given array is not null and has the given minimum size.
*
* @param items the array
* @param minSize the minimum required size
* @param the type of the items in the array
* @throws NullPointerException if the array is null
* @throws IllegalArgumentException if minSize is not positive or the array does not contain minSize elements
*/
public static void checkMinimumSize(T[] items, int minSize) {
checkNonNullInputArray(items);
checkMinSizeIsPositive(minSize);
checkArgument(items.length >= minSize,
"expected at least %s items (actual size: %s)",
minSize, items.length);
}
private static void checkMinSizeIsPositive(int minSize) {
checkArgument(minSize > 0, "number must be positive");
}
/**
* Checks that the given array is not null.
*
* @param items the array
* @param the type of items in the array
* @throws NullPointerException if the array is null
*/
public static void checkNonNullInputArray(T[] items) {
checkNotNull(items, "items cannot be null");
}
}
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