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copley/Java Snippets

Created May 23, 2020
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Java Snippets
package snippets;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.lang.reflect.Array;
import java.nio.charset.StandardCharsets;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.AbstractMap.SimpleEntry;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.OptionalInt;
import java.util.Set;
import java.util.concurrent.ThreadLocalRandom;
import java.util.function.Function;
import java.util.function.IntBinaryOperator;
import java.util.function.IntFunction;
import java.util.function.IntPredicate;
import java.util.function.Predicate;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
public abstract class Snippets {
/**
* Calculates the greatest common denominator (gcd) of an array of numbers
*
* @param numbers Array of numbers
* @return gcd of array of numbers
*/
public static OptionalInt gcd(int[] numbers) {
return Arrays.stream(numbers)
.reduce((a, b) -> gcd(a, b));
}
/**
* Calculates the lowest common multiple (lcm) of an array of numbers.
*
* @param numbers Array of numbers
* @return lcm of array of numbers
*/
public static OptionalInt lcm(int[] numbers) {
IntBinaryOperator lcm = (x, y) -> (x * y) / gcd(x, y);
return Arrays.stream(numbers)
.reduce((a, b) -> lcm.applyAsInt(a, b));
}
private static int gcd(int a, int b) {
if (b == 0) {
return a;
}
return gcd(b, a % b);
}
/**
* Returns the maximum value in an array.
*
* @param numbers Array of numbers
* @return maximum value in an array
*/
public static OptionalInt arrayMax(int[] numbers) {
return Arrays.stream(numbers).max();
}
/**
* Returns the minimum value in an array.
*
* @param numbers Array of numbers
* @return minimum value in an array
*/
public static OptionalInt arrayMin(int[] numbers) {
return Arrays.stream(numbers).min();
}
/**
* Chunks an array into smaller arrays of a specified size.
*
* @param numbers Input array of numbers
* @param size The chunk size
* @return Smaller chunks
*/
public static int[][] chunk(int[] numbers, int size) {
return IntStream.iterate(0, i -> i + size)
.limit((long) Math.ceil((double) numbers.length / size))
.mapToObj(cur -> Arrays.copyOfRange(numbers, cur, cur + size > numbers.length ? numbers.length : cur + size))
.toArray(int[][]::new);
}
/**
* Counts the occurrences of a value in an array.
*
* @param numbers Array of numbers
* @param value the value for which we have to count occurrences
* @return count of total number of occurrences of the value
*/
public static long countOccurrences(int[] numbers, int value) {
return Arrays.stream(numbers)
.filter(number -> number == value)
.count();
}
/**
* Deep flattens an array.
*
* @param input A nested array containing integers
* @return flattened array
*/
public static int[] deepFlatten(Object[] input) {
return Arrays.stream(input)
.flatMapToInt(o -> {
if (o instanceof Object[]) {
return Arrays.stream(deepFlatten((Object[]) o));
}
return IntStream.of((Integer) o);
}).toArray();
}
/**
* Returns the difference between two arrays.
*
* @param first the first array
* @param second the second array
* @return Elements in first that are not in second
*/
public static int[] difference(int[] first, int[] second) {
Set<Integer> set = Arrays.stream(second).boxed().collect(Collectors.toSet());
return Arrays.stream(first)
.filter(v -> !set.contains(v))
.toArray();
}
/**
* Filters out all values from an array for which the comparator function does not return true.
*
* @param first the first array
* @param second the second array
* @param comparator the comparator function
* @return the resulting array
*/
public static int[] differenceWith(int[] first, int[] second, IntBinaryOperator comparator) {
return Arrays.stream(first)
.filter(a ->
Arrays.stream(second)
.noneMatch(b -> comparator.applyAsInt(a, b) == 0)
).toArray();
}
/**
* Returns all the distinct values of an array.
*
* @param elements ints
* @return distinct values
*/
public static int[] distinctValuesOfArray(int[] elements) {
return Arrays.stream(elements).distinct().toArray();
}
/**
* Removes elements in an array until the passed function returns true. Returns the remaining elements in the array.
*
* @param elements
* @param condition
* @return
*/
public static int[] dropElements(int[] elements, IntPredicate condition) {
while (elements.length > 0 && !condition.test(elements[0])) {
elements = Arrays.copyOfRange(elements, 1, elements.length);
}
return elements;
}
/**
* Returns a new array with n elements removed from the right
*
* @param elements
* @param n number of elements to remove
* @return array after removing n elements
*/
public static int[] dropRight(int[] elements, int n) {
if (n < 0) {
throw new IllegalArgumentException("n is less than 0");
}
return n < elements.length
? Arrays.copyOfRange(elements, 0, elements.length - n)
: new int[0];
}
/**
* Returns every nth element in an array.
*
* @param elements
* @param nth
* @return
*/
public static int[] everyNth(int[] elements, int nth) {
return IntStream.range(0, elements.length)
.filter(i -> i % nth == nth - 1)
.map(i -> elements[i])
.toArray();
}
/**
* Filters out the non-unique values in an array.
* <p>
* Use Array.stream().filter() for an array containing only the unique values.
*
* @param elements input array
* @return unique values in the array
*/
public static int[] filterNonUnique(int[] elements) {
return Arrays.stream(elements)
.filter(el -> indexOf(elements, el) == lastIndexOf(elements, el))
.toArray();
}
/**
* Find index of element in the array. Return -1 in case element does not exist.
* <p>
* Uses IntStream.range().filter() to find index of the element in the array.
*
* @param elements input array
* @param el element to find
* @return index of the element
*/
public static int indexOf(int[] elements, int el) {
return IntStream.range(0, elements.length)
.filter(idx -> elements[idx] == el)
.findFirst()
.orElse(-1);
}
/**
* Find last index of element in the array. Return -1 in case element does not exist.
* <p>
* Uses IntStream.iterate().limit().filter() to find index of the element in the array.
*
* @param elements input array
* @param el element to find
* @return index of the element
*/
public static int lastIndexOf(int[] elements, int el) {
return IntStream.iterate(elements.length - 1, i -> i - 1)
.limit(elements.length)
.filter(idx -> elements[idx] == el)
.findFirst()
.orElse(-1);
}
/**
* Flattens an array.
*
* @param elements input array
* @return flattened array
*/
public static int[] flatten(Object[] elements) {
return Arrays.stream(elements)
.flatMapToInt(el -> el instanceof int[]
? Arrays.stream((int[]) el)
: IntStream.of((int) el)
).toArray();
}
/**
* Flattens an array up to the specified depth.
*
* @param elements input array
* @param depth depth to which to flatten array
* @return flattened array
*/
public static Object[] flattenDepth(Object[] elements, int depth) {
if (depth == 0) {
return elements;
}
return Arrays.stream(elements)
.flatMap(el -> el instanceof Object[]
? Arrays.stream(flattenDepth((Object[]) el, depth - 1))
: Arrays.stream(new Object[]{el})
).toArray();
}
/**
* Groups the elements of an array based on the given function.
*
* @param elements input array
* @param func function
* @param <T> type parameter
* @return grouped elements in a Map
*/
public static <T, R> Map<R, List<T>> groupBy(T[] elements, Function<T, R> func) {
return Arrays.stream(elements).collect(Collectors.groupingBy(func));
}
/**
* Returns all the elements of an array except the last one.
* Use Arrays.copyOfRange() to return all except the last one
*
* @param elements
* @param <T>
* @return
*/
public static <T> T[] initial(T[] elements) {
return Arrays.copyOfRange(elements, 0, elements.length - 1);
}
/**
* Initializes an array containing the numbers in the specified range where start and end are inclusive.
*
* @param end
* @param start
* @return
*/
public static int[] initializeArrayWithRange(int end, int start) {
return IntStream.rangeClosed(start, end).toArray();
}
public static int[] initializeArrayWithValues(int n, int value) {
return IntStream.generate(() -> value).limit(n).toArray();
}
public static int[] intersection(int[] first, int[] second) {
Set<Integer> set = Arrays.stream(second).boxed().collect(Collectors.toSet());
return Arrays.stream(first)
.filter(set::contains)
.toArray();
}
public static <T extends Comparable<? super T>> int isSorted(T[] arr) {
final int direction = arr[0].compareTo(arr[1]) < 0 ? 1 : -1;
for (int i = 0; i < arr.length; i++) {
T val = arr[i];
if (i == arr.length - 1) return direction;
else if ((val.compareTo(arr[i + 1]) * direction > 0)) return 0;
}
return direction;
}
public static <T> String join(T[] arr, String separator, String end) {
return IntStream.range(0, arr.length)
.mapToObj(i -> new SimpleEntry<>(i, arr[i]))
.reduce("", (acc, val) -> val.getKey() == arr.length - 2
? acc + val.getValue() + end
: val.getKey() == arr.length - 1 ? acc + val.getValue() : acc + val.getValue() + separator, (fst, snd) -> fst);
}
public static <T> String join(T[] arr, String separator) {
return join(arr, separator, separator);
}
public static <T> String join(T[] arr) {
return join(arr, ",");
}
public static <T> T nthElement(T[] arr, int n) {
if (n > 0) {
return Arrays.copyOfRange(arr, n, arr.length)[0];
}
return Arrays.copyOfRange(arr, arr.length + n, arr.length)[0];
}
public static <T, R> Map<T, R> pick(Map<T, R> obj, T[] arr) {
return Arrays.stream(arr)
.filter(obj::containsKey)
.collect(Collectors.toMap(k -> k, obj::get));
}
public static Map<String, Object>[] reducedFilter(Map<String, Object>[] data, String[] keys, Predicate<Map<String, Object>> fn) {
return Arrays.stream(data)
.filter(fn)
.map(el -> Arrays.stream(keys).filter(el::containsKey)
.collect(Collectors.toMap(Function.identity(), el::get)))
.toArray((IntFunction<Map<String, Object>[]>) Map[]::new);
}
public static <T> T sample(T[] arr) {
return arr[(int) Math.floor(Math.random() * arr.length)];
}
public static <T> T[] sampleSize(T[] input, int n) {
T[] arr = Arrays.copyOf(input, input.length);
int length = arr.length;
int m = length;
while (m > 0) {
int i = (int) Math.floor(Math.random() * m--);
T tmp = arr[i];
arr[i] = arr[m];
arr[m] = tmp;
}
return Arrays.copyOfRange(arr, 0, n > length ? length : n);
}
public static <T> T[] shuffle(T[] input) {
T[] arr = Arrays.copyOf(input, input.length);
int length = arr.length;
int m = length;
while (m > 0) {
int i = (int) Math.floor(Math.random() * m--);
T tmp = arr[i];
arr[i] = arr[m];
arr[m] = tmp;
}
return arr;
}
public static <T> T[] similarity(T[] first, T[] second) {
return Arrays.stream(first)
.filter(a -> Arrays.stream(second).anyMatch(b -> Objects.equals(a, b)))
// Make a new array of first's runtime type, but empty content:
.toArray(i -> (T[]) Arrays.copyOf(new Object[0], i, first.getClass()));
}
public static <T> T[] emptyArray(Class<T> clz) {
return (T[]) Array.newInstance(clz, 0);
}
public static <T extends Comparable<? super T>> int sortedIndex(T[] arr, T el) {
boolean isDescending = arr[0].compareTo(arr[arr.length - 1]) > 0;
return IntStream.range(0, arr.length)
.filter(i -> isDescending ? el.compareTo(arr[i]) >= 0 : el.compareTo(arr[i]) <= 0)
.findFirst()
.orElse(arr.length);
}
public static <T> T[] symmetricDifference(T[] first, T[] second) {
Set<T> sA = new HashSet<>(Arrays.asList(first));
Set<T> sB = new HashSet<>(Arrays.asList(second));
return Stream.concat(
Arrays.stream(first).filter(a -> !sB.contains(a)),
Arrays.stream(second).filter(b -> !sA.contains(b))
).toArray(i -> (T[]) Arrays.copyOf(new Object[0], i, first.getClass()));
}
public static <T> T[] tail(T[] arr) {
return arr.length > 1
? Arrays.copyOfRange(arr, 1, arr.length)
: arr;
}
public static <T> T[] take(T[] arr, int n) {
return Arrays.copyOfRange(arr, 0, n);
}
public static <T> T[] takeRight(T[] arr, int n) {
return Arrays.copyOfRange(arr, arr.length - n, arr.length);
}
public static <T> T[] union(T[] first, T[] second) {
Set<T> set = new HashSet<>(Arrays.asList(first));
set.addAll(Arrays.asList(second));
return set.toArray((T[]) Arrays.copyOf(new Object[0], 0, first.getClass()));
}
public static <T> T[] without(T[] arr, T... elements) {
List<T> excludeElements = Arrays.asList(elements);
return Arrays.stream(arr)
.filter(el -> !excludeElements.contains(el))
.toArray(i -> (T[]) Arrays.copyOf(new Object[0], i, arr.getClass()));
}
public static List<Object[]> zip(Object[]... arrays) {
OptionalInt max = Arrays.stream(arrays).mapToInt(arr -> arr.length).max();
return IntStream.range(0, max.getAsInt())
.mapToObj(i -> Arrays.stream(arrays)
.map(arr -> i < arr.length ? arr[i] : null)
.toArray())
.collect(Collectors.toList());
}
public static Map<String, Object> zipObject(String[] props, Object[] values) {
return IntStream.range(0, props.length)
.mapToObj(i -> new SimpleEntry<>(props[i], i < values.length ? values[i] : null))
.collect(
HashMap::new, (m, v) -> m.put(v.getKey(), v.getValue()), HashMap::putAll);
}
public static double average(int[] arr) {
return IntStream.of(arr)
.average()
.orElseThrow(() -> new IllegalArgumentException("Array is empty"));
}
public static List<String> anagrams(String input) {
if (input.length() <= 2) {
return input.length() == 2
? Arrays.asList(input, input.substring(1) + input.substring(0, 1))
: Collections.singletonList(input);
}
return IntStream.range(0, input.length())
.mapToObj(i -> new SimpleEntry<>(i, input.substring(i, i + 1)))
.flatMap(entry ->
anagrams(input.substring(0, entry.getKey()) + input.substring(entry.getKey() + 1))
.stream()
.map(s -> entry.getValue() + s))
.collect(Collectors.toList());
}
public static int byteSize(String input) {
// Read the link below to learn more
// https://stackoverflow.com/questions/16270994/difference-between-string-length-and-string-getbytes-length
return input.getBytes().length;
}
public static String capitalize(String input, boolean lowerRest) {
return input.substring(0, 1).toUpperCase() +
(lowerRest
? input.substring(1, input.length()).toLowerCase()
: input.substring(1, input.length()));
}
public static String capitalizeEveryWord(final String input) {
return Pattern.compile("\\b(?=\\w)").splitAsStream(input)
.map(w -> capitalize(w, false))
.collect(Collectors.joining());
}
public static int countVowels(String input) {
return input.replaceAll("[^aeiouAEIOU]", "").length();
}
public static String escapeRegExp(String input) {
return Pattern.quote(input);
}
public static String fromCamelCase(String input, String separator) {
return input
.replaceAll("([a-z\\d])([A-Z])", "$1" + separator + "$2")
.toLowerCase();
}
public static boolean isAbsoluteUrl(String url) {
return Pattern.compile("^[a-z][a-z0-9+.-]*:").matcher(url).find();
}
public static boolean isLowerCase(String input) {
return Objects.equals(input, input.toLowerCase());
}
public static boolean isUpperCase(String input) {
return Objects.equals(input, input.toUpperCase());
}
public static String mask(String input, int num, String mask) {
int length = input.length();
return num > 0
?
input.substring(0, length - num).replaceAll(".", mask)
+ input.substring(length - num)
:
input.substring(0, Math.negateExact(num))
+ input.substring(Math.negateExact(num), length).replaceAll(".", mask);
}
public static boolean isPalindrome(String input) {
String s = input.toLowerCase().replaceAll("[\\W_]", "");
return Objects.equals(
s,
new StringBuilder(s).reverse().toString()
);
}
public static String reverseString(String input) {
return new StringBuilder(input).reverse().toString();
}
public static String sortCharactersInString(String input) {
return Arrays.stream(input.split("")).sorted().collect(Collectors.joining());
}
public static String[] splitLines(String input) {
return input.split("\\r?\\n");
}
public static String toCamelCase(String input) {
Matcher matcher = Pattern.compile("[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+").matcher(input);
List<String> matchedParts = new ArrayList<>();
while (matcher.find()) {
matchedParts.add(matcher.group(0));
}
String s = matchedParts.stream()
.map(x -> x.substring(0, 1).toUpperCase() + x.substring(1).toLowerCase())
.collect(Collectors.joining());
return s.substring(0, 1).toLowerCase() + s.substring(1);
}
public static String toKebabCase(String input) {
Matcher matcher = Pattern.compile("[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+").matcher(input);
List<String> matchedParts = new ArrayList<>();
while (matcher.find()) {
matchedParts.add(matcher.group(0));
}
return matchedParts.stream()
.map(String::toLowerCase)
.collect(Collectors.joining("-"));
}
public static List<String> match(String input, String regex) {
Matcher matcher = Pattern.compile(regex).matcher(input);
List<String> matchedParts = new ArrayList<>();
while (matcher.find()) {
matchedParts.add(matcher.group(0));
}
return matchedParts;
}
public static String toSnakeCase(String input) {
Matcher matcher = Pattern.compile("[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+").matcher(input);
List<String> matchedParts = new ArrayList<>();
while (matcher.find()) {
matchedParts.add(matcher.group(0));
}
return matchedParts.stream()
.map(String::toLowerCase)
.collect(Collectors.joining("_"));
}
public static String truncateString(String input, int num) {
return input.length() > num
? input.substring(0, num > 3 ? num - 3 : num) + "..."
: input;
}
public static String[] words(String input) {
return Arrays.stream(input.split("[^a-zA-Z-]+"))
.filter(s -> !s.isEmpty())
.toArray(String[]::new);
}
//Read the link below for more information
// https://stackoverflow.com/questions/309424/read-convert-an-inputstream-to-a-string
public static String convertInputStreamToString(final InputStream in) throws IOException {
ByteArrayOutputStream result = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
int length;
while ((length = in.read(buffer)) != -1) {
result.write(buffer, 0, length);
}
return result.toString(StandardCharsets.UTF_8.name());
}
public static int[] randomInts(int total, int start, int end) {
return ThreadLocalRandom.current().ints(total, start, end).toArray();
}
public String readFileAsString(Path path) throws IOException {
return new String(Files.readAllBytes(path));
}
public static String stackTraceAsString(final Throwable throwable) {
final StringWriter sw = new StringWriter();
throwable.printStackTrace(new PrintWriter(sw));
return sw.toString();
}
public static <T> T[] concat(T[] first, T[] second) {
return Stream.concat(
Stream.of(first),
Stream.of(second)
).toArray(i -> (T[]) Arrays.copyOf(new Object[0], i, first.getClass()));
}
public static String getCurrentWorkingDirectoryPath() {
return FileSystems.getDefault().getPath("").toAbsolutePath().toString();
}
public static boolean isNumeric(final String input) {
if (input == null || input.isEmpty()) {
return false;
}
return IntStream.range(0, input.length())
.allMatch(i -> Character.isDigit(input.charAt(i)));
}
public static int findNextPositivePowerOfTwo(int value) {
return 1 << (32 - Integer.numberOfLeadingZeros(value - 1));
}
public static boolean isEven(final int value) {
return (value & 0b1) == 0;
}
public static boolean isPowerOfTwo(final int value) {
return value > 0 && ((value & (~value + 1)) == value);
}
public static int generateRandomInt() {
return ThreadLocalRandom.current().nextInt();
}
public static String tmpDirName() {
String tmpDirName = System.getProperty("java.io.tmpdir");
if (!tmpDirName.endsWith(File.separator)) {
tmpDirName += File.separator;
}
return tmpDirName;
}
public static String osName() {
return System.getProperty("os.name").toLowerCase();
}
public static boolean isDebuggerAttached() {
final RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
return runtimeMXBean.getInputArguments()
.stream()
.anyMatch(arg -> arg.contains("-agentlib:jdwp"));
}
/**
* Input a line of numbers separated by space as integers
* and return ArrayList of Integers.
* eg. the String "1 2 3 4 5 6 7 8 9" is returned as an ArrayList of Integers.
*
* @param numbers range of numbers separated by space as a string
* @return ArrayList of Integers
*/
public static int[] stringToIntegers(String numbers) {
return Arrays.stream(numbers.split(" ")).mapToInt(Integer::parseInt).toArray();
}
/* Class Utilities */
public static List<Class<?>> getAllInterfaces(final Class<?> cls) {
return Stream.concat(
Arrays.stream(cls.getInterfaces()).flatMap(intf ->
Stream.concat(Stream.of(intf), getAllInterfaces(intf).stream())),
cls.getSuperclass() == null ? Stream.empty() : getAllInterfaces(cls.getSuperclass()).stream()
).distinct().collect(Collectors.toList());
}
public static boolean isInnerClass(final Class<?> cls) {
return cls != null && cls.getEnclosingClass() != null;
}
public static <E extends Enum<E>> Map<String, E> getEnumMap(final Class<E> enumClass) {
return Arrays.stream(enumClass.getEnumConstants())
.collect(Collectors.toMap(Enum::name, Function.identity()));
}
}
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