Java Strings are immutable?

Question

Why are Java strings considered immutable? I can say String name = "Paul"; and later on change name value to name = "Henry";. Where is immutability coming from?

You are not changing the previous string object, instead you are making and assigning new object to `name`. — Adil Soomro, May 14 '13 at 12:17
Five Good Reasons: [Why String is immutable or final in Java](http://javarevisited.blogspot.in/2010/10/why-string-is-immutable-in-java.html) — Grijesh Chauhan, May 14 '13 at 12:18
http://stackoverflow.com/questions/1552301/immutability-of-strings-in-java — Steve P., May 14 '13 at 12:18

NimChimpsky · Answer 1 · 2015-05-07T07:32:56.790

3

A new string is created, they are definitely immutable and interned btw.

You can't do this :

String name = "Paul"; // in effect the same as new String("Paul");
name.setValue("Henry")

becuase a string is immutable you have to create a completely new object.

edited May 07 '15 at 07:32

answered May 14 '13 at 12:17

NimChimpsky

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How and yet name is the object and its value has been changed to "Henry" ? – Paul Odero May 14 '13 at 12:20
@PaulOdero: `name` is not the object. `name` is a reference to a (String) object. At first it's a reference to the `"Paul"` object, later you change that reference to point to the `"Henry"` object. The `"Paul"` object does not change, because it is immutable. – jlordo May 14 '13 at 12:24
@jlordo Does both `"Paul"` `"Henry"` exists in String pool. so that intially `name` pointed to `"Paul"` and then to `"Henry"` – Santhosh May 05 '15 at 15:08
@SanKrish no, see update – NimChimpsky May 07 '15 at 07:33

score 1 · Accepted Answer · answered May 14 '13 at 12:17

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The object itself didn't change.

What you have done is the following

name <- String("Paul")
name <- String("Henry")

String("Paul") has been not been changed.

Try the following:

String a = "test";
String b = a;
a = "test2";

System.out.println(b);

answered May 14 '13 at 12:17

Michal Borek

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score 1 · Answer 3 · answered May 14 '13 at 12:18

Distinguish between the variable: name, which is referring to a String and the String it refers to.

name originally pointed to the String "Paul", later you changed it to point somewhere else, "Paul" itself was unaffected.

Consider

 String name = "Paul";
 String name1 = name;

 name = "Peter";

what does name1 refer to now?

Java Strings are immutable?

3 Answers3