string is immutable ?

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what is the meaning of string is immutable , i read about this topic and i understand that any new operation on that string will create a new object ? Right ??

- -
So if it is right , what is the meaning by below code ?

C#

string x="Hello";
x="good morning";

what the above code meaning ?
is x in the first line and x is the second line are the same ? or they are two different object ?
please i need to understand , so appreciate any demonstration with example , thanks

Posted 8-Mar-14 22:10pm

Hercal

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3 solutions

Solution 3

String is immutable in nature means we can't reassign the the value to the same object.
When we will reassign the value to a variable like

string a="Hello";
a="Hello World";

In the above example first it is creating a object and assigning the "Hello" value. But when reassigning then it keeps the reference of "a" in memory and destroy it and create new object with value "Hello world".

Posted 8-Mar-14 22:48pm

Singh Rajan

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agent_kruger 9-Mar-14 5:01am

1 vote, because it has already been answered correctly. Please don't answer the question which is already being answered and if still answering provide new points.
Sorry sir, if i am rude.

Hercal 9-Mar-14 6:12am

string a="Hello"; a="Hello World";............... [a] is a reference saved in [ stack] it point to an object has value of "hello" which saved in memory [ heap ] then same reference [a] now point to another object with another value saved in heap " hello world" ......is this concept right or wrong ????=============if it is wrong , please clarify and if my concept is right then i have one more question ,....what about the old object ["hello"] when it will be destroyed ? and is there an availability to retrieve it back.??

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Abhinav S · Accepted Answer · 2014-03-08T22:14:00

Solution 1

Strings are immutable.
This means that when you add something to this string or remove a character, a new string is created.
The existing string value reference remains and is not destroyed.

string a = "1";
string b = "2";
string a = a + b;

This code creates a new string in memory called "12" and assigns it to a. "1" still remains and will be collected as and when appropriate.

Posted 8-Mar-14 22:14pm

Abhinav S

Comments

Peter Leow 9-Mar-14 4:22am

clear and concise, 5ed.

Abhinav S 9-Mar-14 6:01am

Thank you.

Hercal 9-Mar-14 4:24am

so they use a string builder which is mutable because of this issue , right ?

Hercal 9-Mar-14 6:14am

string a="Hello"; a="Hello World";............... [a] is a reference saved in [ stack] it point to an object has value of "hello" which saved in memory [ heap ] then same reference [a] now point to another object with another value saved in heap " hello world" ......is this concept right or wrong ????=============if it is wrong , please clarify and if my concept is right then i have one more question ,....what about the old object ["hello"] when it will be destroyed ?

agent_kruger 9-Mar-14 4:58am

sir, nice explanation +5 vote. But i want to ask how to get the "1" back which was stored previously.

Abhinav S 9-Mar-14 6:02am

Thanks. Nope you cant get the 1 back. Try c = "1";
But this is not a guarantee since the old 1 may already have been collected.

agent_kruger 9-Mar-14 7:02am

sir, does collect here means the value is being erased?

Hercal 9-Mar-14 5:44am

Agent_Spock ( nice question )

agent_kruger 9-Mar-14 7:02am

thank you, sir.

Krunal Rohit · Accepted Answer · 2014-03-08T22:27:00

Solution 2

Quote:
String is immutable means that you cannot change the object itself, but you can change the reference ofcourse

For example,

C#

string x="Hello";
x+="good morning";
Console.WriteLine(x);  // will print, Hello good morning

-KR

Posted 8-Mar-14 22:27pm

Krunal Rohit

Updated 8-Mar-14 22:43pm

v2

Comments

Hercal 9-Mar-14 4:30am

ok nice ,now it is clear to me but what about the old object ? when it will be removed from memory ?

Krunal Rohit 9-Mar-14 4:33am

old object reference would be changed by new reference. You can judge it through the output.

-KR

Richard MacCutchan 9-Mar-14 4:38am

No it won't, it will only print "good morning"

Krunal Rohit 9-Mar-14 4:45am

Ans is updated now..
Typo mistake.

-KR