Java

Java RSS

hi.. string compare

Please support our Java advertiser: Programming Forums - DaniWeb Sister Site

•

Join Date: Nov 2006

Posts: 1

Reputation: harisha is an unknown quantity at this point

Solved Threads: 0

harisha

Offline

Newbie Poster

hi.. string compare

Nov 30th, 2006

hi. this is harisha, newbie.

how to compare two strings in java.

.

String id,t;

if (id.compareTo(t) > 2)

{....}

is this correct.while i compile it shows error.

reply me soon..

Last edited by harisha; Nov 30th, 2006 at 5:47 am. Reason: urgent

•

Join Date: Mar 2004

Posts: 765

Reputation: Phaelax is on a distinguished road

Solved Threads: 38

Phaelax

Offline

Master Poster

Re: hi.. string compare

Dec 1st, 2006

what error are you getting?

•

Join Date: Dec 2004

Posts: 4,217

Reputation: peter_budo has much to be proud of

Solved Threads: 489

peter_budo peter_budo is offline

Offline

Code tags enforcer

Re: hi.. string compare

Dec 1st, 2006

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
if(string1.compareTo(string2) == 0)
             STRING EQUALS
else
             STRINGS DO NOT MATCH
if(string1.compareTo(string2) == 0)
             STRING EQUALS
else
             STRINGS DO NOT MATCH

be aware this method can return three values less then zero, zero, or greater then zero. Only equal to zero is string are same

more info on string

Learn to see in another's calamity the ills which you should avoid.
Publilius Syrus
(~100 BC)
LJC - London Java Community, Graduate & Undergraduate Software Development Community, JAVAWUG (Java Web User Group), The London Android Group

•

Join Date: May 2006

Posts: 21

Reputation: java_programmer is an unknown quantity at this point

Solved Threads: 0

java_programmer java_programmer is offline

Offline

Newbie Poster

Re: hi.. string compare

Dec 1st, 2006

You can use equals() method or == operator to compare two Strings instead of compareTo() method.

•

Join Date: Nov 2004

Posts: 6,143

Reputation: jwenting is just really nice

Solved Threads: 212

jwenting

Offline

duckman

Re: hi.. string compare

Dec 1st, 2006

NEVER use == to compare objects. It doesn't work.
It MIGHT work for Strings, but there's NO guarantee.

As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.

•

Join Date: Mar 2004

Posts: 765

Reputation: Phaelax is on a distinguished road

Solved Threads: 38

Phaelax

Offline

Master Poster

Re: hi.. string compare

Dec 1st, 2006

Doesn't == just compare the memory address of two objects to see if its the same? So it'd only return true if the references were the same?

•

Join Date: Aug 2005

Posts: 5,266

Reputation: iamthwee is a splendid one to behold

Solved Threads: 377

iamthwee

Offline

Posting Expert

Re: hi.. string compare

Dec 1st, 2006

I didn't think you could overload operators like that, as you would do in other languages such as c++?

*Voted best profile in the world*

•

Join Date: Mar 2004

Posts: 765

Reputation: Phaelax is on a distinguished road

Solved Threads: 38

Phaelax

Offline

Master Poster

Re: hi.. string compare

Dec 1st, 2006

I tried a little test, and as far as Strings go, these all return as you would expect if you had used equals().

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
String s1 = "test1";
        String s2 = "test";
 
        boolean test1 = ("test" == "test");
        boolean test2 = (s1 == s2);
        s2 = "test1";
        boolean test3 = (s1 == s2);
 
        System.out.println(test1);
        System.out.println(test2);
        System.out.println(test3);
String s1 = "test1";
        String s2 = "test";
        
        boolean test1 = ("test" == "test");
        boolean test2 = (s1 == s2);
        s2 = "test1";
        boolean test3 = (s1 == s2);
        
        System.out.println(test1);
        System.out.println(test2);
        System.out.println(test3);

Using jdk1.5 if it makes a difference.

•

Join Date: Nov 2004

Posts: 6,143

Reputation: jwenting is just really nice

Solved Threads: 212

jwenting

Offline

duckman

Re: hi.. string compare

Dec 2nd, 2006

•

Originally Posted by iamthwee

I didn't think you could overload operators like that, as you would do in other languages such as c++?

You can't.
Java doesn't feature operator overloading.
The only effective operator overloading is the built in support for string concatenation using the + sign.

•

Doesn't == just compare the memory address of two objects to see if its the same? So it'd only return true if the references were the same?

That is correct.
With the existence of the String object pool however and many people first encountering the operator applied to objects (rather than primitives) when trying to compare Strings they often get confused into thinking it does work to compare the content of objects.
Even with Strings though it can in fact fail, depending on how the Strings were constructed.

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
String s1 = "Hello World";
String s2 = "Hello World";
boolean b = s1 == s2;
String s1 = "Hello World";
String s2 = "Hello World";
boolean b = s1 == s2;

will yield true because "Hello World" will be placed on the String object pool and the JVM will assign s2 to the same actual instance as s1.

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
String s1 = "Hello World";
String s2 = new String("Hello World");
boolean b = s1 == s2;
String s1 = "Hello World";
String s2 = new String("Hello World");
boolean b = s1 == s2;

will yield false because here you have forced the JVM to create a new String instance on the heap when defining s2 (containing a clone of the content of s1), thus s1 and s2 don't point to the same instance on the String object pool.

And those are simple examples. In real programs it can get a lot more tricky to figure it out, as the 2 Strings might for example come from deserialised objects received from other programs, previous program runs that stored them on disk, or reflection based generation, performed by classes far removed from your comparison to which you may not have the source.

As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.