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package algs11;
import stdlib.*;
/* ***********************************************************************
* Compilation: javac java
* Execution: java Autoboxing
*
* Headaches with autoboxing. Why does the following code behave
* the way it does?
*
* % java Autoboxing
* 42 and 42 are incomparable
* 43 == 43
* 142 and 142 are incomparable
*
* Explanation:
* - cmp(new Integer(42), new Integer(42))
* first and second refer to different objects holding the value 42;
* thus, first != second.
* The expressions (first < second) and (first > second) autounbox
* the Integer values to 42, so neither expression is true.
*
* - cmp(43, 43)
* the values 43 are autoboxed to the same Integer object because
* Java's Integer implementation caches the objects associated with
* the values -128 to 127 and the valueOf() method uses the cached
* values (and valueOf() gets called by the autoboxing).
*
* - cmp(142, 142)
* the values 142 are autoboxed to different Integer objects.
*
*
*
*************************************************************************/
public class XAutoboxing {
public static void cmp(Integer first, Integer second) {
if (first < second) StdOut.format("%d < %d\n", first, second);
else if (first == second) StdOut.format("%d == %d\n", first, second);
else if (first > second) StdOut.format("%d > %d\n", first, second);
else StdOut.format("%d and %d are incomparable\n", first, second);
}
public static void main(String[] args) {
cmp(new Integer(42), 43);
cmp(new Integer(42), new Integer(42));
cmp(Integer.valueOf(42), Integer.valueOf (42));
cmp(43, 43);
cmp(142, 142);
double x1 = 0.0, y1 = -0.0;
Double a1 = x1, b1 = y1;
//StdOut.println(x1 == y1); /* eclipse warns: comparing identical expression */
StdOut.println(a1.equals(b1));
double x2 = 0.0/0.0, y2 = 0.0/0.0;
Double a2 = x2, b2 = y2;
StdOut.println(x2 != y2);
StdOut.println(!a2.equals(b2));
}
}
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