Strings and equality

[Rrohit rakesh upadhyay]

can anyone please explain the output of the program given below:



class A123
{
public static void main(String args[])
{
String s1="hello123";
String s2="hello"+String.valueOf(123);
String s3="hello"+"123";
String s5=new String("hello123");
if(s1==s2)
System.out.println("s1==s2");
if(s1==s3)
System.out.println("s1==s3");
if(s1==s5)
System.out.println("s1==s5");

if(s2==s3)
System.out.println("s2==s3");
if(s2==s5)
System.out.println("s2==s5");

if(s3==s5)
System.out.println("s3==s5");
System.out.println(s1);
System.out.println(s2);
System.out.println(s3);
System.out.println(s5);

}
}


why s1 is eaqual to s3 and not s2

[Paweł Baczyński]

Have you read this?

[Campbell Ritchie]

Before we give any more answers, please tell us where the question comes from, or whether you wrote it yourself, to avoid problems about copyright.

[Rrohit rakesh upadhyay]

i saw that question on facebook.

[Campbell Ritchie]

Please show us the facebook link.

[Rrohit rakesh upadhyay]

here is the link:

https://m.facebook.com/groups/183792688409636?view=permalink&id=593934157395485&refid=18&_ft_&__tn__=%2As

[Rrohit rakesh upadhyay]

To:Paweł Baczyński

i read the article you suggested and i know" ==" is used to whether the variable refers to the same object or not,and "equals()" is used to match the contents of the variables but i don't understand why s1 is equal to s3 and not equal to s2.

[Paweł Baczyński]

Rrohit rakesh upadhyay wrote:i read the article you suggested and i know" ==" is used to whether the variable refers to the same object or not,and "equals()" is used to match the contents of the variables but i don't understand why s1 is equal to s3 and not equal to s2.

Ok, so now read this

Short story: "hello123" and "hello"+"123" are compile time constants so they go to the string pool. They represent the same string value in the string pool so they are the same object so == gives true.

"hello"+String.valueOf(123) and new String("hello123") are not compile time constants. They are evaluated on runtime creating new objects different from those in string pool, so == gives false..

[Rrohit rakesh upadhyay]

To:Paweł Baczyński


Thank you