DiffableDifferentiator.java

/*******************************************************************************
 * Copyright (c) 1998, 2015 Oracle and/or its affiliates. All rights reserved.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *     Oracle - initial API and implementation from Oracle TopLink
******************************************************************************/
package org.eclipse.persistence.tools.workbench.utility.diff;

/**
 * This differentiator delegates to the actual objects being compared.
 * The two objects are "identical" if either
 *     they are both null
 * or
 *     object 1 says they are
 *
 * All of the behavior for this class is paremeterized,
 * allowing us to use a singleton.
 */
public class DiffableDifferentiator implements Differentiator {

    // singleton
    private static DiffableDifferentiator INSTANCE;

    /**
     * Return the singleton.
     */
    public static synchronized Differentiator instance() {
        if (INSTANCE == null) {
            INSTANCE = new DiffableDifferentiator();
        }
        return INSTANCE;
    }

    /**
     * Ensure non-instantiability.
     */
    private DiffableDifferentiator() {
        super();
    }

    /**
     * @see Differentiator#diff(Object, Object)
     */
    public Diff diff(Object object1, Object object2) {
        return this.diff(object1, object2, DiffableAdapter.NORMAL);
    }

    /**
     * @see Differentiator#keyDiff(Object, Object)
     */
    public Diff keyDiff(Object object1, Object object2) {
        return this.diff(object1, object2, DiffableAdapter.KEY);
    }

    private String fatalDescriptionTitle() {
        return "The two objects cannot be compared";
    }

    private Diff diff(Object object1, Object object2, DiffableAdapter adapter) {
        if (object1 == object2) {
            return new NullDiff(object1, object2, this);
        }
        if ((object1 == null) || (object2 == null)) {
            return new SimpleDiff(object1, object2, this.fatalDescriptionTitle(), this);
        }
        return adapter.diff((Diffable) object1, object2);
    }

    /**
     * @see Differentiator#comparesValueObjects()
     */
    public boolean comparesValueObjects() {
        return false;
    }

    /**
     * @see Object#toString()
     */
    public String toString() {
        return "DiffableDifferentiator";
    }

}