== comparison

[bobby chaurasia]

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) {
System.out.println("True");
}
else{
System.out.println("True");
}
On running it printed "true".
Any comments ?

[Brian Glodde]

The 2nd part of your if/then has a typo. It should be
System.out.println("False");
Then you should see the desired result.

[Anthony Villanueva]

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:

 
public class Testing
{
public static void main( String args[] ) 
{
Integer a = new Integer(5);
Integer b = new Integer(5);

if (a == b) 
{
System.out.println("True"); 
}
else
{
System.out.println("False"); 
}

Integer c = a;

if (a == c) 
{
System.out.println("True"); 
}
else
{
System.out.println("False"); 
}
}
}

The output should be:
False
True
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

[Anthony Villanueva]

BTW if you wish to compare your Integers, use
a.intValue() == b.intValue()
instead.
-anthony

[Rob Ross]

Or just good old-fashioned equals()...

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