whats the difference between == and equals

[savita jadhav]

can some explain me the difference between == and equals?
why equals is used with object ans string only?
savita

[parag kulkarni]

hi savita !
There is a lots of difference in both. == does only "coparision" that is as visible to our eye as well say a string or numbers etc. But with equals() the comparision is deeper
For example 1-1-2001 and 1-jan-2001 are equal from the 'moment in time" consideration so == will return false whilst equals() will return true if used with apropriate calsses.
I hope that explains it all.
parag kulkarni
mumbai

[Rekha Sivadasan]

equals is a method defined in the Object class. It operates on objects and takes in an argument of Object and returns a boolean value. It has been declared as public boolean equals(Object o). This method has been overriden in various classes like String, Boolean, Integer etc.
In String class equals compares the characters inside String object, whereas == compares object references.
The same holds good for Integer class. equals method - where the actual int value is compared whereas == compares object references.
Check the following programme out. It will make things more clear.
class EqualsTest{
public static void main(String arg[]){
String a = new String("Test");
String a1 = new String("Test");
Integer i = new Integer(100);
Integer i1 = new Integer(100);
System.out.println("a.equals(a1) " + a.equals(a1));
System.out.println("i.equals(i1) " + i.equals(i1));
System.out.println(a == a1);
System.out.println(i == i1);

}
}
Hope this helps.
Rekha

[kaffo lekan]

What about this code,is the test for == correct.
class EqualsTest{
public static void main(String arg[]){
String a = "Test";
String a1 = "Test";
Integer i = 100;
Integer i1 = 100;
System.out.println("a.equals(a1) " + a.equals(a1));
System.out.println("i.equals(i1) " + i.equals(i1));
System.out.println(a == a1);
System.out.println(i == i1);

}
}
what is the output.
thanks

[Rekha Sivadasan]

You get a compile time error for the programme since you can't create an Integer object like that.
As far as String are concerned both the output will be true since Strings are immutable and when similar strings are created without the new keyword both a and a1 refer to the same object.

[savita jadhav]

thanks everybody for solving my problem.got the concept
savita

[Sandeep Nachane]

Savita,
You may find the self review questions on my homepages useful, if you need to test your == and equals() concepts. http://www.tipsmart.com/javacert/selfreview/objequiv.htm
-Sandeep Nachane