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 * 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

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 */

package jdk.internal.vm.compiler.collections;

/**

 * Strategy for comparing two objects. Default predefined strategies are {@link #DEFAULT},

 * {@link #IDENTITY}, and {@link #IDENTITY_WITH_SYSTEM_HASHCODE}.

 *

 * @since 19.0

 */

public abstract class Equivalence {

    /**

     * Default equivalence calling {@link #equals(Object)} to check equality and {@link #hashCode()}

     * for obtaining hash values. Do not change the logic of this class as it may be inlined in

     * other places.

     *

     * @since 19.0

     */

    public static final Equivalence DEFAULT = new Equivalence() {

        @Override

        public boolean equals(Object a, Object b) {

            return a.equals(b);

        }

        @Override

        public int hashCode(Object o) {

            return o.hashCode();

        }

    };

    /**

     * Identity equivalence using {@code ==} to check equality and {@link #hashCode()} for obtaining

     * hash values. Do not change the logic of this class as it may be inlined in other places.

     *

     * @since 19.0

     */

    public static final Equivalence IDENTITY = new Equivalence() {

        @Override

        public boolean equals(Object a, Object b) {

            return a == b;

        }

        @Override

        public int hashCode(Object o) {

            return o.hashCode();

        }

    };

    /**

     * Identity equivalence using {@code ==} to check equality and

     * {@link System#identityHashCode(Object)} for obtaining hash values. Do not change the logic of

     * this class as it may be inlined in other places.

     *

     * @since 19.0

     */

    public static final Equivalence IDENTITY_WITH_SYSTEM_HASHCODE = new Equivalence() {

        @Override

        public boolean equals(Object a, Object b) {

            return a == b;

        }

        @Override

        public int hashCode(Object o) {

            return System.identityHashCode(o);

        }

    };

    /**

     * Subclass for creating custom equivalence definitions.

     *

     * @since 19.0

     */

    protected Equivalence() {

    }

    /**

     * Returns {@code true} if the non-{@code null} arguments are equal to each other and

     * {@code false} otherwise.

     *

     * @since 19.0

     */

    public abstract boolean equals(Object a, Object b);

    /**

     * Returns the hash code of a non-{@code null} argument {@code o}.

     *

     * @since 19.0

     */

    public abstract int hashCode(Object o);

}