api/src/main/java/javax/jdo/identity/SingleFieldIdentity.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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
<<<<<<< Updated upstream
 *
 *     https://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
=======
 * 
 *     https://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 
>>>>>>> Stashed changes
 * limitations under the License.
 */

/*
 * SingleFieldIdentity.java
 *
 */

package javax.jdo.identity;

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import javax.jdo.JDOFatalInternalException;
import javax.jdo.JDONullIdentityException;
import javax.jdo.spi.I18NHelper;

/**
 * This class is the abstract base class for all single field identity classes. A common case of
 * application identity uses exactly one persistent field in the class to represent identity. In
 * this case, the application can use a standard JDO class instead of creating a new user-defined
 * class for the purpose.
 *
 * @version 2.0
 */
public abstract class SingleFieldIdentity<SUBCLASS extends SingleFieldIdentity<SUBCLASS>>
    implements Externalizable, Comparable<SUBCLASS> {

  private static final long serialVersionUID = 1L;

  /** The Internationalization message helper. */
  protected static final I18NHelper MSG = I18NHelper.getInstance("javax.jdo.Bundle"); // NOI18N

  /** The class of the target object. */
  private transient Class<?> targetClass;

  /** The name of the class of the target object. */
  private String targetClassName;

  /** The hashCode. */
  protected int hashCode;

  /** The key as an Object. */
  protected Object keyAsObject;

  /**
   * Constructor with target class.
   *
   * @param pcClass the class of the target
   * @since 2.0
   */
  protected SingleFieldIdentity(Class<?> pcClass) {
    if (pcClass == null) throw new NullPointerException();
    targetClass = pcClass;
    targetClassName = pcClass.getName();
  }

  /**
   * Constructor only for Externalizable.
   *
   * @since 2.0
   */
  public SingleFieldIdentity() {}

  /**
   * Set the given key as the key for this instance. Compute the hash code for the instance.
   *
   * @param key The key to use
   * @since 2.0
   */
  protected void setKeyAsObject(Object key) {
    assertKeyNotNull(key);
    keyAsObject = key;
  }

  /**
   * Assert that the key is not null. Throw a JDONullIdentityException if the given key is null.
   *
   * @param key The key to check
   * @since 2.0
   */
  protected void assertKeyNotNull(Object key) {
    if (key == null) {
      throw new JDONullIdentityException(MSG.msg("EXC_SingleFieldIdentityNullParameter")); // NOI18N
    }
  }

  /**
   * Return the target class.
   *
   * @return the target class.
   * @since 2.0
   */
  public Class<?> getTargetClass() {
    return targetClass;
  }

  /**
   * Return the target class name.
   *
   * @return the target class name.
   * @since 2.0
   */
  public String getTargetClassName() {
    return targetClassName;
  }

  /**
   * Return the key as an Object. The method is synchronized to avoid race conditions in
   * multi-threaded environments.
   *
   * @return the key as an Object.
   * @since 2.0
   */
  public synchronized Object getKeyAsObject() {
    if (keyAsObject == null) {
      keyAsObject = createKeyAsObject();
    }
    return keyAsObject;
  }

  /**
   * Create the key as an Object.
   *
   * @return the key as an Object;
   * @since 2.0
   */
  protected Object createKeyAsObject() {
    throw new JDOFatalInternalException(MSG.msg("EXC_CreateKeyAsObjectMustNotBeCalled"));
  }

  /**
   * Check the class and class name and object type. If restored from serialization, class will be
   * null so compare class name.
   *
   * @param obj the other object
   * @return true if the class or class name is the same
   */
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    } else if (obj == null || this.getClass() != obj.getClass()) {
      return false;
    } else {
      SingleFieldIdentity<?> other = (SingleFieldIdentity<?>) obj;
      if (targetClass != null && targetClass == other.targetClass) return true;
      return targetClassName.equals(other.targetClassName);
    }
  }

  /**
   * Return the hash code of the class name.
   *
   * @return the hash code of the class name
   * @since 2.0
   */
  protected int hashClassName() {
    return targetClassName.hashCode();
  }

  /**
   * Return the cached hash code.
   *
   * @return the cached hash code.
   */
  public int hashCode() {
    return hashCode;
  }

  /**
   * Write to the output stream.
   *
   * @param out the stream
   */
  public void writeExternal(ObjectOutput out) throws IOException {
    out.writeObject(targetClassName);
    out.writeInt(hashCode);
  }

  /** Read from the input stream. Creates a new instance with the target class name set */
  public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
    targetClass = null;
    targetClassName = (String) in.readObject();
    hashCode = in.readInt();
  }

  /**
   * Determine the ordering of identity objects. Only the class name is compared. This method is
   * only used by subclasses.
   *
   * @param o Other identity
   * @return The relative ordering between the objects
   * @since 2.2
   */
  protected int compare(SingleFieldIdentity<?> o) {
    return targetClassName.compareTo(o.targetClassName);
  }
}