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jtstand-desktop is a gui library, an extension of swing. jtstand-desktop is derived from swingx.

There is a newer version: 1.2.1

/*
 * Copyright (c) 2009 Albert Kurucz.
 *
 * This file, Contract.java is part of JTStand.
 *
 * JTStand is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * JTStand 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with JTStand.  If not, see .
 */
package org.jdesktop.swingx.util;


/**
 * Utility class for checking contracts.
 * 
 * @author Jeanette Winzenburg
 */
public class Contract {

    private Contract() {
        
    }

    /**
     * Tests the input parameter against null. If the input is 
     * an array, checks all of its elements as well. Returns the 
     * unchanged parameter if not null, throws a NullPointerException
     * otherwise. 
     * 
     * PENDING: type of exception? there are raging debates, some
     *   favour an IllegalArgument? 
     *   
     * PENDING: the implementation uses a unchecked type cast to an array.
     *   can we do better, how?
     *     
     * 
     * @param  the type of the input parameter
     * @param input the argument to check against null.
     * @param message the text of the exception if the argument is null
     * @return the input if not null
     * @throws NullPointerException if input is null
     */
    @SuppressWarnings("unchecked")
    public static  T asNotNull(T input, String message) {
        if (input == null) 
            throw new NullPointerException(message);
        
        if (input.getClass().isArray()) {
            if (!input.getClass().getComponentType().isPrimitive()) {
                T[] array = (T[]) input;
                for (int i = 0; i < array.length; i++) {
                    asNotNull(array[i], message);
                }
            }
        }
        
        return input;
    }
}