core/src/com/google/inject/internal/util/Objects.java

/*
 * Copyright (C) 2007 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.inject.internal.util;

import com.google.inject.internal.Nullable;
import java.util.Arrays;

/**
 * Helper functions that can operate on any {@code Object}.
 *
 * @author Laurence Gonsalves
 */
public final class Objects {
  private Objects() {}

  /**
   * Determines whether two possibly-null objects are equal. Returns:
   *
   * <ul>
   * <li>{@code true} if {@code a} and {@code b} are both null.
   * <li>{@code true} if {@code a} and {@code b} are both non-null and they are
   *     equal according to {@link Object#equals(Object)}.
   * <li>{@code false} in all other situations.
   * </ul>
   *
   * <p>This assumes that any non-null objects passed to this function conform
   * to the {@code equals()} contract.
   */
  public static boolean equal(@Nullable Object a, @Nullable Object b) {
    return a == b || (a != null && a.equals(b));
  }

  /**
   * Generates a hash code for multiple values. The hash code is generated by
   * calling {@link Arrays#hashCode(Object[])}.
   *
   * <p>This is useful for implementing {@link Object#hashCode()}. For example,
   * in an object that has three properties, {@code x}, {@code y}, and
   * {@code z}, one could write:
   * <pre>
   * public int hashCode() {
   *   return Objects.hashCode(getX(), getY(), getZ());
   * }</pre>
   *
   * <b>Warning</b>: When a single object is supplied, the returned hash code
   * does not equal the hash code of that object.
   */
  public static int hashCode(Object... objects) {
    return Arrays.hashCode(objects);
  }
}