org.openl.util.CollectionUtils Maven / Gradle / Ivy
package org.openl.util;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Objects;
/**
* An util class for collections and arrays.
*
* @author Yury Molchan
*/
public class CollectionUtils {
/**
* Return {@code true} if a collection is null or is empty.
*
* @param col the checked collection.
* @return return {@code true} if the collection does not contain any elements.
* @see Collection#isEmpty()
*/
public static boolean isEmpty(Collection col) {
return col == null || col.isEmpty();
}
/**
* Return {@code true} if a collection contains at least one element. This method is inverse to
* {@link #isEmpty(Collection)}.
*
* @param col the checked collection.
* @return {@code true} if the collection contains at least one element.
*/
public static boolean isNotEmpty(Collection col) {
return !isEmpty(col);
}
/**
* Return {@code true} if a map is null or is empty.
*
* @param map the checked map.
* @return return {@code true} if the map does not contain any elements.
* @see Map#isEmpty()
*/
public static boolean isEmpty(Map map) {
return map == null || map.isEmpty();
}
/**
* Return {@code true} if a map contains at least one element. This method is inverse to {@link #isEmpty(Map)}.
*
* @param map the checked map.
* @return {@code true} if the map contains at least one element.
*/
public static boolean isNotEmpty(Map map) {
return !isEmpty(map);
}
/**
* Return {@code true} if an array is null or is empty.
*
* @param array the checked array.
* @return return {@code true} if the array does not contain any elements.
*/
public static boolean isEmpty(T[] array) {
return array == null || array.length == 0;
}
/**
* Return {@code true} if an array contains at least one element. This method is inverse to {@link #isEmpty(T[])}.
*
* @param array the checked array.
* @return {@code true} if the array contains at least one element.
*/
public static boolean isNotEmpty(T[] array) {
return !isEmpty(array);
}
/**
* Return {@code true} if an array is null or is empty.
*
* @param array the checked array.
* @return return {@code true} if the array does not contain any elements.
* @throws IllegalArgumentException if the argument is not an array.
* @see Array#getLength(Object)
*/
public static boolean isEmpty(T array) {
return array == null || Array.getLength(array) == 0;
}
/**
* Return {@code true} if an array contains at least one element. This method is inverse to {@link #isEmpty(T[])}.
*
* @param array the checked array.
* @return {@code true} if the array contains at least one element.
* @throws IllegalArgumentException if the argument is not an array.
*/
public static boolean isNotEmpty(T array) {
return !isEmpty(array);
}
/**
* Returns a new Collection consisting of the elements of the input collection transformed by the given transformer.
*
*
* @param the type of object in the input collection.
* @param the type of object in the output collection.
* @param col the collection to get the input from, may be null.
* @param mapper the mapper to use.
* @return the transformed result (new list).
* @throws NullPointerException if the mapper is null.
*/
public static List map(Iterable col, Mapper mapper) {
if (col == null) {
return null;
}
Objects.requireNonNull(mapper, "mapper cannot be null");
int size = col instanceof Collection ? ((Collection) col).size() : 0;
ArrayList result = new ArrayList<>(size);
for (I input : col) {
O output = mapper.map(input);
result.add(output);
}
return result;
}
/**
* Finds the first element in the given collection which matches the given predicate.
*
*
* @param the type of object the {@link Iterable} contains.
* @param col the collection to search, may be null.
* @param predicate the predicate to use.
* @return the first element of the collection which matches the predicate or null if none could be found.
* @throws NullPointerException if the predicate is null.
*/
public static T findFirst(Iterable col, Predicate predicate) {
if (col == null) {
return null;
}
Objects.requireNonNull(predicate, "predicate cannot be null");
for (final T item : col) {
if (predicate.evaluate(item)) {
return item;
}
}
return null;
}
/**
* Selects all elements from input collection which match the given predicate into an output collection.
*
*
* @param the type of object the {@link Iterable} contains.
* @param col the collection to search, may be null.
* @param predicate the predicate to use.
* @return the all the elements of the collection which matches the predicate or [] if none could be found or null
* if the input collection is null.
* @throws NullPointerException if the predicate is null.
*/
public static List findAll(Iterable col, Predicate predicate) {
if (col == null) {
return null;
}
Objects.requireNonNull(predicate, "predicate cannot be null");
int size = col instanceof Collection ? ((Collection) col).size() : 0;
ArrayList result = new ArrayList<>(size);
for (final T item : col) {
if (predicate.evaluate(item)) {
result.add(item);
}
}
return result;
}
/**
* Checks an array on {@code null} value.
*
* @param array the checked array.
* @param the element type of checked array.
* @return {@code true} if the array contains {@code null}.
*/
public static boolean hasNull(T[] array) {
for (T item : array) {
if (item == null) {
return true;
}
}
return false;
}
public static Object toArray(Collection list, Class instanceClass) {
if (list == null) {
return null;
}
Object result = Array.newInstance(instanceClass, list.size());
int i = 0;
for (Object el : list) {
Array.set(result, i, el);
i++;
}
return result;
}
/**
* Defines a functor interface implemented by classes that map one object into another.
*
* A Mapper converts the input object to the output object. The input object should be left unchanged.
*
* @param the input type to the mapper.
* @param the output type from the mapper.
*/
public interface Mapper {
/**
* Maps the input object (leaving it unchanged) into some output object.
*
* @param input the object to be mapped, should be left unchanged.
* @return a mapped object.
*/
O map(I input);
}
/**
* Defines a functor interface implemented by classes that perform a predicate test on an object.
*
* A Predicate is the object equivalent of an if statement. It uses the input object to
* return a true or false value, and is often used in validation or filtering.
*
*
* @param the type that the predicate queries.
*/
public interface Predicate {
/**
* Use the specified parameter to perform a test that returns true or false.
*
* @param object the object to evaluate, should not be changed.
* @return true or false.
*/
boolean evaluate(T object);
}
}