/*******************************************************************************
 * Copyright (c) 2000, 2003 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials 
 * are made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jface.util;

 
/**
 * <code>Assert</code> is useful for for embedding runtime sanity checks
 * in code. The static predicate methods all test a condition and throw some
 * type of unchecked exception if the condition does not hold.
 * <p>
 * Assertion failure exceptions, like most runtime exceptions, are
 * thrown when something is misbehaving. Assertion failures are invariably
 * unspecified behavior; consequently, clients should never rely on
 * these being thrown (or not thrown). <b>If you find yourself in the
 * position where you need to catch an assertion failure, you have most 
 * certainly written your program incorrectly.</b>
 * </p>
 * <p>
 * Note that an <code>assert</code> statement is slated to be added to the
 * Java language in JDK 1.4, rending this class obsolete.
 * </p>
 */
public final class Assert {
	
	/**
	 * <code>AssertionFailedException</code> is a runtime exception thrown
	 * by some of the methods in <code>Assert</code>.
	 * <p>
	 * This class is not declared public to prevent some misuses; programs that catch 
	 * or otherwise depend on assertion failures are susceptible to unexpected
	 * breakage when assertions in the code are added or removed.
	 * </p>
	 */
	private static class AssertionFailedException extends RuntimeException {

		/**
		 * Constructs a new exception.
		 */
		public AssertionFailedException() {
		}
		
		/**
		 * Constructs a new exception with the given message.
		 */
		public AssertionFailedException(String detail) {
		    super(detail);
		}
	}
/* This class is not intended to be instantiated. */
private Assert() {
}
/**
 * Asserts that an argument is legal. If the given boolean is
 * not <code>true</code>, an <code>IllegalArgumentException</code>
 * is thrown.
 *
 * @param expression the outcome of the check
 * @return <code>true</code> if the check passes (does not return
 *    if the check fails)
 * @exception IllegalArgumentException if the legality test failed
 */
public static boolean isLegal(boolean expression) {
	// succeed as quickly as possible
	if (expression) {
		return true;
	}
	return isLegal(expression, "");//$NON-NLS-1$
}
/**
 * Asserts that an argument is legal. If the given boolean is
 * not <code>true</code>, an <code>IllegalArgumentException</code>
 * is thrown.
 * The given message is included in that exception, to aid debugging.
 *
 * @param expression the outcome of the check
 * @param message the message to include in the exception
 * @return <code>true</code> if the check passes (does not return
 *    if the check fails)
 * @exception IllegalArgumentException if the legality test failed
 */
public static boolean isLegal(boolean expression, String message) {
	if (!expression)
		throw new IllegalArgumentException("assertion failed; " + message); //$NON-NLS-1$
	return expression;
}
/**
 * Asserts that the given object is not <code>null</code>. If this
 * is not the case, some kind of unchecked exception is thrown.
 * <p>
 * As a general rule, parameters passed to API methods must not be
 * <code>null</code> unless <b>explicitly</b> allowed in the method's
 * specification. Similarly, results returned from API methods are never
 * <code>null</code> unless <b>explicitly</b> allowed in the method's
 * specification. Implementations are encouraged to make regular use of 
 * <code>Assert.isNotNull</code> to ensure that <code>null</code> 
 * parameters are detected as early as possible.
 * </p>
 * 
 * @param object the value to test
 * @exception Throwable an unspecified unchecked exception if the object
 *   is <code>null</code>
 */
public static void isNotNull(Object object) {
	// succeed as quickly as possible
	if (object != null) {
		return;
	}
	isNotNull(object, "");//$NON-NLS-1$
}
/**
 * Asserts that the given object is not <code>null</code>. If this
 * is not the case, some kind of unchecked exception is thrown.
 * The given message is included in that exception, to aid debugging.
 * <p>
 * As a general rule, parameters passed to API methods must not be
 * <code>null</code> unless <b>explicitly</b> allowed in the method's
 * specification. Similarly, results returned from API methods are never
 * <code>null</code> unless <b>explicitly</b> allowed in the method's
 * specification. Implementations are encouraged to make regular use of 
 * <code>Assert.isNotNull</code> to ensure that <code>null</code> 
 * parameters are detected as early as possible.
 * </p>
 * 
 * @param object the value to test
 * @param message the message to include in the exception
 * @exception Throwable an unspecified unchecked exception if the object
 *   is <code>null</code>
 */
public static void isNotNull(Object object, String message) {
	if (object == null)
		throw new AssertionFailedException("null argument;" + message);//$NON-NLS-1$
}
/**
 * Asserts that the given boolean is <code>true</code>. If this
 * is not the case, some kind of unchecked exception is thrown.
 *
 * @param expression the outcome of the check
 * @return <code>true</code> if the check passes (does not return
 *    if the check fails)
 */
public static boolean isTrue(boolean expression) {
	// succeed as quickly as possible
	if (expression) {
		return true;
	}
	return isTrue(expression, "");//$NON-NLS-1$
}
/**
 * Asserts that the given boolean is <code>true</code>. If this
 * is not the case, some kind of unchecked exception is thrown.
 * The given message is included in that exception, to aid debugging.
 *
 * @param expression the outcome of the check
 * @param message the message to include in the exception
 * @return <code>true</code> if the check passes (does not return
 *    if the check fails)
 */
public static boolean isTrue(boolean expression, String message) {
	if (!expression)
		throw new AssertionFailedException("Assertion failed: "+message);//$NON-NLS-1$
	return expression;
}
}