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Programmer Certification (OCPJP)

== question

Greenhorn

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posted 23 years ago

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Would someone please tell me why this would print "False". Thank you.
--Tom
==========
1: Byte b1 = new Byte("127");
2:
3: if(b1.toString() == b1.toString())
4: System.out.println("True");
5: else
6: System.out.println("False");

Hemal Mehta

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Posts: 101

posted 23 years ago

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Theere are several of these questions answered earlier.Check earlier postings..

rahil qamar

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posted 23 years ago

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Herculis
Once you have converted byte to a String, all the methods of String are applicable. The "==" operator checks the memory to which it is referencing. Since the addresses are different , you get a false as the answer. However if you wish to match the contents of the two operands, then do a ".equals()" instead
Rahil

rahil

Prasad Ballari

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Posts: 149

posted 23 years ago

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Hi,
Whenever you call toString() method on any object,the toString() method creates new String by using new operator.If any string created by 'new' opearator will not be in the String pool (that usually happens if u create String without new keyword),hence == operator is not refering to the same memory address.Thats why the the answer is false.
HTH
Prasad

herkulis nugent

Greenhorn

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posted 23 years ago

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Thanks, Prasad. So how can one find out if a string already exists in the string pool? Also, does it follow that that toString() always create new String object even if there's one in the pool?
--Tom
=========

Originally posted by Prasad Ballari:
Hi,
Whenever you call toString() method on any object,the toString() method creates new String by using [b]new operator.If any string created by 'new' opearator will not be in the String pool (that usually happens if u create String without new keyword),hence == operator is not refering to the same memory address.Thats why the the answer is false.
HTH
Prasad[/B]

Prasad Ballari

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posted 23 years ago

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herkulis/Tom,
We need not worry about whether specified string exists in the String pool or not ;as the compiler will do it for you.As the String objects are immutable in nature; the compiler tries to optimise and save some memory by refering it from pool as it knows the String object value is not going to change (because of its immutable nature).
NB: You can put a String in to the pool by calling intern() method
HTH
-Prasad Ballari

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asim wagan

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Posts: 62

posted 23 years ago

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<html><body>
Here is a modification to your program so that it prints TRUE. Using intern() method:
<code>
class sringbyte{
public static void main(String ard[]){
Byte b1 = new Byte("127");
if(b1.toString().intern() == b1.toString().intern())
System.out.println("True");
else
System.out.println("False");
}
}</code>
The string false was printed because each time when you use the toString() method for object you create it creates a new string in the pool. So, to cover it up you can use the intern() method.</body></html>

Don't get me started about those stupid light bulbs.