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== comparison

bobby chaurasia
Ranch Hand

Joined: Mar 30, 2002
Posts: 84
IN java rule round-up I came across the following question:
Integer a = new Integer(5);
Integer b = new Integer(5);
What is the result of running: if( a == b)
I choose true. On checking the answers the It read as false. Not convinced I compiled the code
public static void main( String args[] ) {
Integer a = new Integer(5);
Integer b = new Integer(5);
if (a == b) {
On running it printed "true".
Any comments ?
Brian Glodde
Ranch Hand

Joined: Jun 27, 2001
Posts: 171
The 2nd part of your if/then has a typo. It should be
Then you should see the desired result.
Anthony Villanueva
Ranch Hand

Joined: Mar 22, 2002
Posts: 1055
This expression (a == b) compares the addresses in memory of the objects, not a test of equality of state. Since a and b are two distinct objects, a == b is false, as Brian correctly pointed out. If two references point to the same object, however, the result should be true.
The proof of the pudding is in the eating, they say , so:

The output should be:
Beware of String literals though. Given
String s = "Hello!";
String t = "Hello!";
the String references s and t point to the same object. But
String p = new String("Hello!");
String q = new String("Hello!");
the String references p and q point to different objects!
Anthony Villanueva
Ranch Hand

Joined: Mar 22, 2002
Posts: 1055
BTW if you wish to compare your Integers, use
a.intValue() == b.intValue()
Rob Ross

Joined: Jan 07, 2002
Posts: 2205
Or just good old-fashioned equals()...

if (a.equals(b))...

SCJP 1.4
I agree. Here's the link:
subject: == comparison
It's not a secret anymore!