Java Puzzle : Integer Initialization
Here is a simple program which instantiate Integer object using primitive int values with all possible ways, new operator, AutoBoxing, Integer.valueOf() .
1: package com.test;
2: 3: public class IntegerPuzzle {
4: public static void main(String[] args) {
5: Integer a = new Integer(100);
6: Integer b = new Integer(100);
7: Integer c = 100; 8: Integer d = 100; 9: Integer e = Integer.valueOf(100); 10: Integer f = 150; 11: Integer g = 150; 12: 13: System.out.println("a = b ? " + (a==b));
14: System.out.println("c = d ? " + (c==d));
15: System.out.println("d = e ? " + (d==e));
16: System.out.println("a = c ? " + (a==c));
17: System.out.println("f = g ? " + (f==g));
18: } 19: }What would be the output of this program ?
a = b ? false
ReplyDeletec = d ? true
d = e ? true
a = c ? false
f = g ? false
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Confusion is (c==d) and (f==g) comparisons.
Found out that if value is between -128 to 127, then it returns true. Else false
Integer f = 127;
Integer g = 127;
f==g is true
Integer f = 128;
Integer g = 128;
f==g is false
Integer f = -128;
Integer g = -128;
f==g is true
Integer f = -129;
Integer g = -129;
f==g is false
Interesting, that it is working true for 1 byte range.
You are correct dude :)
ReplyDeleteWhy ?
Actually like String class, Integer class also provides caching for better performance. By default it caches only -128 to 128 range of int values ,as these are most used int values. This cache is being used in only two cases
1. Autoboxing
2. Integer.valueOf().
In case of new operator , this caching mechanism will get bypassed.
Developer can increase the cache size by passing runtime argument.
Greatt blog post
ReplyDelete