FinalCollections.java Source code

Introduction

Here is the source code for FinalCollections.java

Source

/*
 *     file: FinalCollections.java
 *  package: oreilly.hcj.finalstory
 *
 * This software is granted under the terms of the Common Public License,
 * CPL, which may be found at the following URL:
 * http://www-124.ibm.com/developerworks/oss/CPLv1.0.htm
 *
 * Copyright(c) 2003-2005 by the authors indicated in the @author tags.
 * All Rights are Reserved by the various authors.
 *
 ########## DO NOT EDIT ABOVE THIS LINE ########## */

import java.awt.Color;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

/**
 * Demonstrates the use of final collections.
 * 
 * @author <a href=mailto:kraythe@arcor.de>Robert Simmons jr. (kraythe)</a>
 * @version $Revision: 1.3 $
 */
public class FinalCollections {
    /**
     * Main method for demonstration.
     * 
     * @param args
     *          Command line arguments.
     */
    public static final void main(final String[] args) {
        Rainbow.someMethod();
        System.out.println("------------------");
        try {
            RainbowBetter.someMethod();
        } catch (final UnsupportedOperationException ex) {
            ex.printStackTrace(System.out);
            System.out.println("Told you it would exception =)");
        }
    }

    /**
     * A class that demonstrates the rainbow.
     * 
     * @author <a href=mailto:kraythe@arcor.de>Robert Simmons jr. (kraythe)</a>
     * @version $Revision: 1.3 $
     */
    public static class Rainbow {
        /** The set of valid colors of the rainbow. */
        public static final Set VALID_COLORS;

        static {
            VALID_COLORS = new HashSet();
            VALID_COLORS.add(Color.red);
            VALID_COLORS.add(Color.orange);
            VALID_COLORS.add(Color.yellow);
            VALID_COLORS.add(Color.green);
            VALID_COLORS.add(Color.blue);
            VALID_COLORS.add(Color.decode("#4B0082")); // indigo
            VALID_COLORS.add(Color.decode("#8A2BE2")); // violet
        }

        /**
         * A demo method.
         */
        public static final void someMethod() {
            Set colors = Rainbow.VALID_COLORS;
            colors.add(Color.black); // <= logic error but allowed by compiler
            System.out.println(colors);
        }
    }

    /**
     * A better version of the rainbow class using an unmodifiable set.
     * 
     * @author <a href=mailto:kraythe@arcor.de>Robert Simmons jr. (kraythe)</a>
     * @version $Revision: 1.3 $
     */
    public static class RainbowBetter {
        /** The valid colors of the rainbow. */
        public static final Set VALID_COLORS;

        static {
            Set temp = new HashSet();
            temp.add(Color.red);
            temp.add(Color.orange);
            temp.add(Color.yellow);
            temp.add(Color.green);
            temp.add(Color.blue);
            temp.add(Color.decode("#4B0082")); // indigo
            temp.add(Color.decode("#8A2BE2")); // violet
            VALID_COLORS = Collections.unmodifiableSet(temp);
        }

        /**
         * Some demo method.
         */
        public static final void someMethod() {
            Set colors = RainbowBetter.VALID_COLORS;
            colors.add(Color.black); // <= exception here
            System.out.println(colors);
        }
    }
}

/* ########## End of File ########## */