BaseHasUuid.java

/*
 * #%L
 * FlatPack serialization code
 * %%
 * Copyright (C) 2012 Perka 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.
 * #L%
 */
package com.getperka.flatpack;

import java.util.UUID;

/**
 * Utility base class that provides lazy UUID generation.
 */
public class BaseHasUuid implements HasUuid {
  private UUID uuid;

  /**
   * Equal to any {@link HasUuid} type with the same UUID and where one type is assignable to
   * another.
   */
  @Override
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }
    if (!(obj instanceof HasUuid)) {
      return false;
    }
    return getUuid().equals(((HasUuid) obj).getUuid())
      && (getClass().isAssignableFrom(obj.getClass()) ||
      obj.getClass().isAssignableFrom(getClass()));
  }

  /**
   * Generates a new UUID by calling {@link #defaultUuid()} if a value has not been previously set.
   */
  @Override
  public UUID getUuid() {
    if (uuid == null) {
      uuid = defaultUuid();
    }
    return uuid;
  }

  /**
   * Calls {@code getUuid().hashCode()}.
   */
  @Override
  public int hashCode() {
    return getUuid().hashCode();
  }

  @Override
  public void setUuid(UUID uuid) {
    this.uuid = uuid;
  }

  /**
   * Returns a random UUID. Subclasses can override this method to change the value returned by
   * {@link #getUuid()}.
   */
  protected UUID defaultUuid() {
    return UUID.randomUUID();
  }
}