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A small collection of Java utilities for every-day use
package com.github.ormfux.common.utils;
import static com.github.ormfux.common.utils.NullableUtils.isNull;
import static com.github.ormfux.common.utils.NullableUtils.nonNull;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.function.Function;
import java.util.function.Predicate;
public final class CollectionUtils {
private CollectionUtils() {
throw new IllegalAccessError(CollectionUtils.class.getSimpleName() + " class is not intended to be instantiated");
}
/**
* Maps from source collection to a target collection.
*
* @param source type
* @param target type
* @param source source collection
* @param result target collection
* @param functor mapping functor
* @return target collection
*/
public static Collection map(final S[] source, final Collection result, final Function functor) {
Objects.requireNonNull(result);
Objects.requireNonNull(functor);
for (final S sourceElement : source) {
result.add(functor.apply(sourceElement));
}
return result;
}
/**
* Maps from source collection to a target collection. ONly elements from the source collection that satisfy the filter
* condition will be mapped and included in the result.
*
* @param source type
* @param target type
* @param source source collection
* @param result target collection
* @param filterCondition the filter condition
* @param mapFunction mapping functor
* @return target collection
*/
public static Collection filterAndMap(final Collection source, final Collection result, final Predicate filterCondition, final Function mapFunction) {
Objects.requireNonNull(result);
Objects.requireNonNull(filterCondition);
Objects.requireNonNull(mapFunction);
for (final S sourceElement : source) {
if (filterCondition.test(sourceElement)) {
result.add(mapFunction.apply(sourceElement));
}
}
return result;
}
/**
* Maps from source collection to a target collection.
*
* @param source type
* @param target type
* @param source source collection
* @param result target collection
* @param functor mapping functor
* @return target collection
*/
public static Collection map(final Collection source, final Collection result, final Function functor) {
Objects.requireNonNull(result);
Objects.requireNonNull(functor);
for (final S sourceElement : source) {
result.add(functor.apply(sourceElement));
}
return result;
}
/**
* Maps from source collection to a target array.
*
* @param source source collection
* @param functor mapping functor
* @return target array
*
* @param source type
* @param target type
*
*/
@SuppressWarnings("unchecked")
public static T[] mapToArray(final Collection source, final Function functor) {
Objects.requireNonNull(functor);
final List resultList = new ArrayList<>(source.size());
for (final S sourceElement : source) {
final T executeResult = functor.apply(sourceElement);
if (nonNull(executeResult)) {
// add the non-null results to the list only
resultList.add(executeResult);
}
}
return (T[]) resultList.toArray();
}
/**
* Filters a source collection and add result to a target collection.
*
* @param source/target type
* @param source source collection
* @param result target collection
* @param predicate filtering predicate
* @return target array
*/
public static Collection filter(final Collection source, final Collection result, final Predicate predicate) {
Objects.requireNonNull(result);
Objects.requireNonNull(predicate);
for (final T sourceElement : source) {
if (predicate.test(sourceElement)) {
result.add(sourceElement);
}
}
return result;
}
/**
* Checks whether a collection is {@code null} or empty.
*
* @param type
* @param collection collection
* @return true, if {@code null} or empty
*/
public static boolean isEmpty(final Collection collection) {
return NullableUtils.check(collection, NullableUtils.isEmpty(), true);
}
/**
* Returns the first element from the given collection that evaluates the given predicate to
* {@code true}.
*
* @param Parameterized type.
*
* @param collection a collection.
* @param predicate The predicate.
* @return the first element from the given collection that evaluates the given predicate to
* {@code true}; {@code null} when there is none.
*/
public static T selectFirst(final Collection collection, final Predicate predicate) {
Objects.requireNonNull(predicate);
for (final T sourceElement : collection) {
if (predicate.test(sourceElement)) {
return sourceElement;
}
}
return null;
}
/**
* Determines whether an element in the given collection evaluates the given predicate to
* {@code true}.
*
* @param Parameterized type.
*
* @param collection a collection.
* @param predicate a predicate.
*
* @return {@code true} when there is an element in the collection fulfilling the predicate.
*/
public static boolean exists(final Collection collection, final Predicate predicate) {
Objects.requireNonNull(predicate);
for (final T sourceElement : collection) {
if (predicate.test(sourceElement)) {
return true;
}
}
return false;
}
/**
* Compares two collections for equality. The elements in both collections should be unique,
* otherwise the result might not be very accurate.
*
* @param Parameterized type.
*
* @param col1 source collection.
* @param col2 target collection.
*
* @return {@code true} both collections have the same size and contain the same elements.
*/
public static boolean isEqual(final Collection col1, final Collection col2) {
if (col1 == col2) {
return true;
} else if ((isNull(col1) && nonNull(col2)) || (nonNull(col1) && isNull(col2))) {
return false;
} else if (col1.size() != col2.size()) {
return false;
} else {
final List remainingContents = new ArrayList(col1);
for (final T col2Element : col2) {
if (!remainingContents.remove(col2Element)) {
return false;
}
}
return remainingContents.isEmpty();
}
}
/**
* Converts a collection to a map. The function is used to produce the map keys.
*
* @param key type
* @param entry type
*
* @param source source collection
* @param keyFunction Function to produce the map keys.
* @return The map.
*/
public static Map asMap(final Collection source, final Function keyFunction) {
return asMap(source, keyFunction, Function.identity());
}
/**
* Converts a collection to a map.
*
* @param key type
* @param map value type
* @param collection element type
*
* @param source source collection
* @param keyFunction Function to produce the map keys.
* @param valueFunction Function to produce the map values.
* @return The collection as map.
*/
public static Map asMap(final Collection source,
final Function keyFunction,
final Function valueFunction) {
final Map map = new HashMap<>();
for (final E sourceElement : source) {
map.put(keyFunction.apply(sourceElement), valueFunction.apply(sourceElement));
}
return map;
}
}