Byte

[Fisher Daniel]

Hi all,
I have code :
class A
{
public static void main(String[] args)
{
Byte a = new Byte("127");
if (a.toString() == a.toString())
System.out.println("True");
else
System.out.println("False");
}
}
Why the answer is "False" ?
thanks
daniel

[Guoqiao Sun]

Hi, the reason is, every time the .toString() method return a new String object. Two new String objects comparison will return false even they contain same text inside.
Hope it helps.

------------------
Guoqiao Sun
Sun Certified Programmer for Java™ 2 Platform
try my mock exam¹²³ at my homepage.

[Mark Seegers]

But:

class Str{
public static void main(String[] args){
String a = "hello";
String b = "hello";
if (a == b){
System.out.println("True");
} else {
System.out.println("False");
}
}
}

returns True. So why doesn't the first example?

[tvs sundaram]

WE WILL ANALYSE YOUR CODE
--------------------
class Str{
public static void main(String[] args){ String a = "hello";// THIS IS A STRING LITERAL
String b = "hello";// AND ALSO THIS
// STRING LITERALS ARE NOT OBJECTS
// THEY ARE CREATED IN STRING POOL
// HERE IN String a,b YOU R REFERING TO THE SAME LITERAL
// HENCE NO FREASH STRING IS CRETED FOR YOUR SECOND STATEMENT
// THAT IS String b="hello" WILL BE THE SME LITERAL AS GENERATED
// USING String a="hello" UT VARIABLE b ALSO POINTS TO IT
// THEY ARE NOT FOR GARBAGE COLLECTION
// NOW DOING == OPERATION REFERS TO THE SAME STRING IN STRING POOL
// AND HENCE
if (a == b){ System.out.println("True");// CORRECT }
else { System.out.println("False"); }
}}
HOPE THIS HELPS
tvs sundaram
SCP for Java 2 Platform

[Geoff Tate]

Mark,
the reason is the way java handles strings. When you create a string literal, java adds it to an internal table. Since strings are immutable, there is no need to keep multiple copies of the same data. So since you already created "hello", it is added to the table. "hello" is again looked up and found in the table when you add a reference to b. since a & b now point to the same reference to "hello", they are indeed equal. I believe that if you were to have said b = new String("hello"), then you would have received false because a new strinq object would have been created. There is a little used method on the String object called intern() which would add the value of the string object to the interal string table.