SWTError.java

/*******************************************************************************
 * Copyright (c) 2000, 2008, 2012 IBM Corporation, Gerhardt Informatics Kft. and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Gerhardt Informatics Kft. - GEFGWT port
 *******************************************************************************/
package org.eclipse.swt;

import org.eclipse.swt.internal.Library;

/**
 * This error is thrown whenever an unrecoverable error occurs internally in
 * SWT. The message text and error code provide a further description of the
 * problem. The exception has a <code>throwable</code> field which holds the
 * underlying throwable that caused the problem (if this information is
 * available (i.e. it may be null)).
 * <p>
 * SWTErrors are thrown when something fails internally which either leaves SWT
 * in an unknown state (eg. the o/s call to remove an item from a list returns
 * an error code) or when SWT is left in a known-to-be-unrecoverable state (eg.
 * it runs out of callback resources). SWTErrors should not occur in typical
 * programs, although "high reliability" applications should still catch them.
 * </p>
 * <p>
 * This class also provides support methods used by SWT to match error codes to
 * the appropriate exception class (SWTError, SWTException, or
 * IllegalArgumentException) and to provide human readable strings for SWT error
 * codes.
 * </p>
 * 
 * @see SWTException
 * @see SWT#error(int)
 * @see <a href="http://www.eclipse.org/swt/">Sample code and further
 *      information</a>
 */

public class SWTError extends Error {
	/**
	 * The SWT error code, one of SWT.ERROR_*.
	 */
	public int code;

	/**
	 * The underlying throwable that caused the problem, or null if this
	 * information is not available.
	 */
	public Throwable throwable;

	static final long serialVersionUID = 3833467327105808433L;

	/**
	 * Constructs a new instance of this class with its stack trace filled in.
	 * The error code is set to an unspecified value.
	 */
	public SWTError() {
		this(SWT.ERROR_UNSPECIFIED);
	}

	/**
	 * Constructs a new instance of this class with its stack trace and message
	 * filled in. The error code is set to an unspecified value. Specifying
	 * <code>null</code> as the message is equivalent to specifying an empty
	 * string.
	 * 
	 * @param message
	 *            the detail message for the exception
	 */
	public SWTError(String message) {
		this(SWT.ERROR_UNSPECIFIED, message);
	}

	/**
	 * Constructs a new instance of this class with its stack trace and error
	 * code filled in.
	 * 
	 * @param code
	 *            the SWT error code
	 */
	public SWTError(int code) {
		this(code, SWT.findErrorText(code));
	}

	/**
	 * Constructs a new instance of this class with its stack trace, error code
	 * and message filled in. Specifying <code>null</code> as the message is
	 * equivalent to specifying an empty string.
	 * 
	 * @param code
	 *            the SWT error code
	 * @param message
	 *            the detail message for the exception
	 */
	public SWTError(int code, String message) {
		super(message);
		this.code = code;
	}

	/**
	 * Returns the underlying throwable that caused the problem, or null if this
	 * information is not available.
	 * <p>
	 * NOTE: This method overrides Throwable.getCause() that was added to
	 * JDK1.4. It is necessary to override this method in order for inherited
	 * printStackTrace() methods to work.
	 * </p>
	 * 
	 * @return the underlying throwable
	 * 
	 * @since 3.1
	 */
	public Throwable getCause() {
		return throwable;
	}

	/**
	 * Returns the string describing this SWTError object.
	 * <p>
	 * It is combined with the message string of the Throwable which caused this
	 * SWTError (if this information is available).
	 * </p>
	 * 
	 * @return the error message string of this SWTError object
	 */
	public String getMessage() {
		if (throwable == null)
			return super.getMessage();
		return super.getMessage() + " (" + throwable.toString() + ")"; //$NON-NLS-1$ //$NON-NLS-2$
	}

	/**
	 * Outputs a printable representation of this error's stack trace on the
	 * standard error stream.
	 * <p>
	 * Note: printStackTrace(PrintStream) and printStackTrace(PrintWriter) are
	 * not provided in order to maintain compatibility with CLDC.
	 * </p>
	 */
	public void printStackTrace() {
		super.printStackTrace();
		if (Library.JAVA_VERSION < Library.JAVA_VERSION(1, 4, 0)
				&& throwable != null) {
			System.err.println("*** Stack trace of contained error ***"); //$NON-NLS-1$
			throwable.printStackTrace();
		}
	}

}