If String is immutable, why is the following code working ?

[Nagashri Kadur]

public static void main(String[] args) {
String str1 = new String("This is a string");
str1 = "I thought this was immutable !! \n How \t did \t this \t happen ? ";
System.out.println("str1 = " + str1 );
}

The above mentioned code is compiling and is resulting in the following being displayed.
str1 = I thought this was immutable !!
How did this happen ?
If String is immutable how is this working ?

[Henry Wong]

Nagashri Kadur wrote: public static void main(String[] args) {
String str1 = new String("This is a string");
str1 = "I thought this was immutable !! \n How \t did \t this \t happen ? ";
System.out.println("str1 = " + str1 );
}

The above mentioned code is compiling and is resulting in the following being displayed.
str1 = I thought this was immutable !!
How did this happen ?
If String is immutable how is this working ?

Can you tell us the difference between an object and a reference?

Henry

[Nagashri Kadur]

Henry Wong wrote:

Nagashri Kadur wrote: public static void main(String[] args) {
String str1 = new String("This is a string");
str1 = "I thought this was immutable !! \n How \t did \t this \t happen ? ";
System.out.println("str1 = " + str1 );
}

The above mentioned code is compiling and is resulting in the following being displayed.
str1 = I thought this was immutable !!
How did this happen ?
If String is immutable how is this working ?

Can you tell us the difference between an object and a reference?

Henry

When you pass by reference, you pass the address. Am I correct ?

[Nagashri Kadur]

When you pass by reference, the address gets passed. So, any changes made will be reflected. Is that right ?

[Henry Wong]

Nagashri Kadur wrote:When you pass by reference, the address gets passed. So, any changes made will be reflected. Is that right ?

The question was ... can you tell us the difference between an object and a reference? which is very different from can you tell us the difference between "pass by reference" and "pass by value"? Both are very important to understand, but for this question, you need to understand the first distinction -- not the second.


To answer the question. Yes, string objects are immutable. And your example does not refute that. And you need to understand the difference between an object and reference first.

Henry

[Nagashri Kadur]

Oh... OK. Guess there is way more to this than I thought. Thank you Henry ! Let me read up the difference... I really appreciate your guidance

[fred rosenberger]

look at this code:

public static void main(String[] args) { 
  String str1 = new String("This is a string"); 
  String str2 = str1;
  str1 = "I thought this was immutable !! \n How \t did \t this \t happen ? "; 
  System.out.println("str1 = " + str1 ); 
  System.out.println("str2 = " + str2");
} 

and see if that helps you understand.

[Jesper de Jong]

One key thing to understand is: Variables are references. A variable is not the object itself - it's a reference to an object.

String objects are immutable. But if you have a variable that refers to a String object, you can still change the value of the variable itself (making it refer to another String object).