IconRepository.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.framework.resources;

import javax.swing.Icon;

/**
 * Interface used by UI components to fetch icons based on
 * icon keys. This allows a level of indirection between the UI
 * code and the actual icon. The UI code can be ignorant of
 * the location and construction of the icons.
 */
public interface IconRepository {

    /**
     * Return true if the repository has an icon for the given key.
     * Use this before calling getIcon(String) to avoid creating
     * numerous MissingIconExceptions.
     */
    boolean hasIcon(String key);

    /**
     * Return the icon for the specified key.
     * Throw an exception if the icon is not found. Call
     * hasIcon(String) first to avoid getting an exception when
     * the icon does not exist.
     * Return null if the key is null, this allows for
     * situations where some objects have icons
     * and some do not; the objects without icons can
     * simply return null for their icon keys.
     * Also, null will be returned if a particular repository
     * cannot, or should not, supply an icon for the key.
     */
    Icon getIcon(String key);


    // ********** null implementation **********

    /**
     * This instance will throw an exception for any non-null key
     * and return null for any null key.
     */
    IconRepository NULL_INSTANCE =
        new IconRepository() {
            public boolean hasIcon(String key) {
                return key == null;
            }
            public Icon getIcon(String key) {
                if (key == null) {
                    return null;
                }
                throw new MissingIconException("Missing icon file resource name: " + key, key);
            }
            public String toString() {
                return "NullIconRepository";
            }
        };

}