What is the diff. b/w "==" and ".equals( )" Operators

[Kamran Mughni Siddiqui]

Q, What is the basic difference b/w == and .equals()operators..
e.g:
public class Kamran{
public static void main(String[]args){
String aa=("Kamran");//it is in pool
String bb=new String ("Kamran");//it is in heep
System.out.println(aa==bb);
System.out.println(aa.equals(bb));
}
}
Output:
false
true
what does the "==" and ".equals()" operators do in this code ?
Note:Please try to explain with examples...
Thanx in advance
Kamran(Badarian)

[This message has been edited by Kamran Mughni Siddiqui (edited November 16, 2001).]

[Ragu Sivaraman]

Originally posted by Kamran Mughni Siddiqui:
Q, What is the basic difference b/w == and .equals()operators..
e.g:
public class Kamran{
public static void main(String[]args){
String aa=("Kamran");//it is in pool
String bb=new String ("Kamran");//it is in heep
System.out.println(aa==bb);
System.out.println(aa.equals(bb));
}
}
Output:
false
true
what does the "==" and ".equals()" operators do in this code ?
Note:Please try to explain with examples...
Thanx in advance
Kamran(Badarian)

[This message has been edited by Kamran Mughni Siddiqui (edited November 16, 2001).]

== //Shallow comparison
equals() //Deep comparison
if aa = bb; //then both the reference refer to single litreal Kamran and == will be true
But "Kamran" and new String("Kamran") are different and therefore == will be false
HIH
Ragu

[Valentin Crettaz]

== is for comparing primitive values and object references.
int i=1;
int j=1;
int k=2;
i==j yields true, while i==k yields false.
Integer i1 = new Integer(1);
Integer i2 = new Integer(1);
Integer i3 = i2;
i1 == i2 yields false because i1 and i2 reference different Integer instances. i1.equals(i2) yields true because the integer value held by i1 and i2 are the same.
i3 == i2 yields true since i2 and i3 reference the same object and the operator == compares the references of variables.
equals() is only for comparing equality of objects. See example above.
HIH
------------------
Valentin Crettaz
Sun Certified Programmer for Java 2 Platform

[Vikrama Sanjeeva]

Hi Kamran,
== is the coditional operator.It's basic function is to checks the two operands(one on it's left & one on it's right ) for equality.If they are equal then it prints true & vice versa.This opeartor is used in two cases.
1: With variables(Primitives)//As Valentin Crettaz mentioned
2: With reference variable(Non primitive)
Case:1
When used with simple variables i.e primitives it checks the values present in variables.
Example:

        
    int a=9;
    int b=9;
    System.out.println(a==b);

Out Put will be true
Since here it matches the values presnt in the variables a & b.

Case:2
When used with reference variables i.e non primitive, it checks there references.
Example:

String aa=("Kamran");//it is in pool
String bb=new String ("Kamran");/*it is in heep [B]& it is created using new.Therefore always a new reference is selected*/
System.out.println(aa==bb); /*Prints false since aa is refernce variable in pool & bb is reference variable in heap.i.e both are different references*/

equals()[/B].It is very simple one
It's function is to do a [b]deep matching.Deep matching means to match the contents refer by refernce variable.

String aa=("Kamran");//it is in pool
String bb=new String ("Kamran");//it is in heep
System.out.println(aa.equals(bb)); /* Now it matches the object/content refer by refernce variables which is equal, hence it prints true*/

Bye.
Viki.
------------------
Count the flowers of ur garden,NOT the leafs which falls away!
[This message has been edited by Vikrama Sanjeeva (edited November 17, 2001).]