org.glassfish.jersey.internal.util.collection.ImmutableCollectors Maven / Gradle / Ivy

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package org.glassfish.jersey.internal.util.collection;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collector;

/**
 * Set of convenient function regarding a collection immutability. Particularly useful in the conjunction with
 * {@link java.util.stream.Stream}.
 */
public class ImmutableCollectors {

    /**
     * Creates a {@link Collector} of an immutable list for {@link java.util.stream.Stream#collect(Collector)}.
     *
     * @param  type of the immutable list.
     * @return collector for immutable list.
     */
    public static  Collector, List> toImmutableList() {
        return Collector.of(ArrayList::new, List::add, (left, right) -> {
            left.addAll(right);
            return left;
        }, Collections::unmodifiableList);
    }

    /**
     * Creates a {@link Collector} of an immutable Set for {@link java.util.stream.Stream#collect(Collector)}.
     *
     * @param  type of the immutable set.
     * @return collector for immutable set.
     */
    public static  Collector, Set> toImmutableSet() {
        return Collector.of(HashSet::new, Set::add, (left, right) -> {
            left.addAll(right);
            return left;
        }, Collections::unmodifiableSet);
    }

    /**
     * Creates a {@link Collector} of an immutable Set for {@link java.util.stream.Stream#collect(Collector)}.
     *
     * @param  type of the immutable linked hash set.
     * @return collector for immutable linked hash set.
     */
    public static  Collector, Set> toImmutableLinkedSet() {
        return Collector.of(LinkedHashSet::new, Set::add, (left, right) -> {
            left.addAll(right);
            return left;
        }, Collections::unmodifiableSet);
    }
}