001package algs11;
002import stdlib.*;
003/* ***********************************************************************
004 *  Compilation:  javac java
005 *  Execution:  java Autoboxing
006 *
007 *  Headaches with autoboxing. Why does the following code behave
008 *  the way it does?
009 *
010 *  % java Autoboxing
011 *  42 and 42 are incomparable
012 *  43 == 43
013 *  142 and 142 are incomparable
014 *
015 *  Explanation:
016 *    - cmp(new Integer(42), new Integer(42))
017 *      first and second refer to different objects holding the value 42;
018 *      thus, first != second.
019 *      The expressions (first < second) and (first > second) autounbox
020 *      the Integer values to 42, so neither expression is true.
021 *
022 *   - cmp(43, 43)
023 *     the values 43 are autoboxed to the same Integer object because
024 *     Java's Integer implementation caches the objects associated with
025 *     the values -128 to 127 and the valueOf() method uses the cached
026 *     values (and valueOf() gets called by the autoboxing).
027 *
028 *   - cmp(142, 142)
029 *     the values 142 are autoboxed to different Integer objects.
030 *
031 *
032 *
033 *************************************************************************/
034
035public class XAutoboxing {
036
037        public static void cmp(Integer first, Integer second) {
038                if (first < second)       StdOut.format("%d < %d\n", first, second);
039                else if (first == second) StdOut.format("%d == %d\n", first, second);
040                else if (first > second)  StdOut.format("%d > %d\n", first, second);
041                else                      StdOut.format("%d and %d are incomparable\n", first, second);
042        }
043
044        public static void main(String[] args) {                
045                cmp(new Integer(42), 43);
046                cmp(new Integer(42), new Integer(42));
047                cmp(Integer.valueOf(42), Integer.valueOf (42));
048                cmp(43, 43);
049                cmp(142, 142);
050
051                double x1 = 0.0, y1 = -0.0;
052                Double a1 = x1, b1 = y1;
053                //StdOut.println(x1 == y1); /* eclipse warns: comparing identical expression */
054                StdOut.println(a1.equals(b1));
055
056                double x2 = 0.0/0.0, y2 = 0.0/0.0;
057                Double a2 = x2, b2 = y2;
058                StdOut.println(x2 != y2);
059                StdOut.println(!a2.equals(b2));
060        }
061
062}