src/jdk.internal.vm.compiler/share/classes/jdk.internal.vm.compiler.collections/src/jdk/internal/vm/compiler/collections/UnmodifiableEconomicSet.java

/*
 * Copyright (c) 2017, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */


package jdk.internal.vm.compiler.collections;

/**
 * Unmodifiable memory efficient set data structure.
 *
 * @since 1.0
 */
public interface UnmodifiableEconomicSet<E> extends Iterable<E> {

    /**
     * Returns {@code true} if this set contains a mapping for the {@code element}.
     *
     * @since 1.0
     */
    boolean contains(E element);

    /**
     * Returns the number of elements in this set.
     *
     * @since 1.0
     */
    int size();

    /**
     * Returns {@code true} if this set contains no elements.
     *
     * @since 1.0
     */
    boolean isEmpty();

    /**
     * Stores all of the elements in this set into {@code target}. An
     * {@link UnsupportedOperationException} will be thrown if the length of {@code target} does not
     * match the size of this set.
     *
     * @return an array containing all the elements in this set.
     * @throws UnsupportedOperationException if the length of {@code target} does not equal the size
     *             of this set.
     * @since 1.0
     */
    default E[] toArray(E[] target) {
        if (target.length != size()) {
            throw new UnsupportedOperationException("Length of target array must equal the size of the set.");
        }

        int index = 0;
        for (E element : this) {
            target[index++] = element;
        }

        return target;
    }
}