== confusion

[kavin kumar]

class str2
{
public static void main(String a[])
{
//line1
   str2 s2 = new str2();
//line2
   Object o = s2;
 
int r = 0;
   if(s2==o)
     { System.out.println(r+=1);
     }
 
   if (s2.equals(o))
   {
 System.out.println(r+=1);
     }
 
   if (o.equals(s2))
   {
 System.out.println(r+=1);
     }
}
}
 

I had the same kind of question in Kathy sierra book. But i dont understand their explanation. Plz help me with this.

I think (s2 == o ) should return false;
since they r refering to 2 different objects.
Correct me if iam wrong ?Explain me why?

Thanks in advance
Kavin
[ August 16, 2005: Message edited by: Mark Spritzler ]

[Marcelo Ortega]

When used with object refernces, the == operator checks to see if the references refer to same object. In your case o and s2 refer to the same object because they were made aliases when you did:

Object o = s2;

This made o refer to the object which s2 was refering to at the time, and therefor the equality test will return true.

Remember though, that the operands of the == operator (when comparing references) must be found in the same class heirarchy.

hth, cheers.

[Mark Spritzler]

Deleted your duplicate post. Please refrain from duplicate posting. Thanks

Mark

[kavin kumar]

Sorry mark !I wont.

Hello marzo,

Still iam not clear. Plz take a look at this eg.

Acc. to this one how do u explain?I dont know how to explain my confusion that's why i wrote this eg.

String s1 = new String("abc");
String s3= "abc";
String s4 = "abc";


if(s3==s4)
{ System.out.println("EQ");
}

if(s1==s3)
{ System.out.println("Not good");
}
if(s1.equals(s3))
{ System.out.println("Good");
}
}

[Fes D Gaur]

When you use the new key word you are creating a new String object here for s1. Then for s2 you are referring to a second object. s3 simply latches onto the same object s2 is referring to because of string pooling. Therefore s1==s2 will be false because they are two different objects. s1.equals(s2) or s1.equals(s3) will return true because now you are comparing the contents of the objects.

Fes

[naraharirao mocherla]

HI Kavin Kumar
according to ur code.

whenver u create a string with new key word.it will be given a memory address.
if u create a string using just String s1= "abc";
then this string will be in a pool.
if u create another string with same contents ,but without new keyword then that string will go the already existing string pool.(where "abc "is there);

So ,
s1==s3 gives "NOT GOOD":// references are not same.
s3==s4 gives "EQ".references are same.

s1.equals(s3) gives "Good".// character by character is exactly the same.


According to ur code

String s1 = new String("abc");
String s3= "abc";
String s4 = "abc";
 

if(s3==s4)
{ System.out.println("EQ");
}
 
if(s1==s3)
{ System.out.println("Not good");
}
if(s1.equals(s3))
{ System.out.println("Good");
}
}   

[nagaraj raja]

Hai
== USED TO COMPARE REFERENCE VARIABLES REFEREING TO SAME TO CLASS OR NOT
.equals() USED TO COMPARE THE CONTENT OF THE OBJECTS