/*

 * Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.awt;

/**

 * Thrown when code that is dependent on a keyboard, display, or mouse

 * is called in an environment that does not support a keyboard, display,

 * or mouse. Any code that depends on any of those devices should firstly

 * ensure their availability using the {@code GraphicsEnvironment.isHeadless()}

 * method and throw {@code HeadlessException} if the latter returns

 * {@code true}.

 *

 * @since 1.4

 * @author  Michael Martak

 * @see GraphicsEnvironment#isHeadless

 */

public class HeadlessException extends UnsupportedOperationException {

    /*

     * JDK 1.4 serialVersionUID

     */

    private static final long serialVersionUID = 167183644944358563L;

    /**

     * Constructs new {@code HeadlessException} with empty message.

     * For such {@code HeadlessException} the default headless error message

     * may be auto-generated for some platforms.

     * The text of the default headless message may depend on

     * whether the GraphicsEnvironment is in fact headless.

     * That is, the default headless message is both system and environmentally

     * dependent.

     */

    public HeadlessException() {}

    /**

     * Create a new instance with the specified detailed error message.

     * For some platforms the default headless error message may be

     * added at the end of the specified message.

     * The text of the default headless message may depend on

     * whether the GraphicsEnvironment is in fact headless.

     * That is, the default headless message is both system and environmentally

     * dependent.

     *

     * @param  msg the error message

     */

    public HeadlessException(String msg) {

        super(msg);

    }

    /**

     * Returns the detail message string of this {@code HeadlessException}.

     * Depending on the platform the message specified in the constructor may

     * be followed by the default headless error message.

     * The text of the default headless message may depend on

     * whether the GraphicsEnvironment is in fact headless.

     * That is, the default headless message is both system and environmentally

     * dependent.

     *

     * @return  the detail message string of this {@code HeadlessException}

     *          instance (which may be {@code null}).

     */

    public String getMessage() {

        String superMessage = super.getMessage();

        String headlessMessage = GraphicsEnvironment.getHeadlessMessage();

        if (superMessage == null) {

            return headlessMessage;

        } else if (headlessMessage == null) {

            return superMessage;

        } else {

            return superMessage + headlessMessage;

        }

    }

}