Why String is Immutable | Java Tutorial

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Why String is Immutable | Java Tutorial

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[hireme]

Sorry, but your theory and example does not make any sense. Below is the reason for String being immutable

Security: parameters are typically represented as String in network connections, database connection urls, usernames/passwords etc. If it were mutable, these parameters could be easily changed.
Synchronization and concurrency: making String immutable automatically makes them thread safe thereby solving the synchronization issues.
Caching: when compiler optimizes your String objects, it sees that if two objects have same value (a="test", and b="test") and thus you need only one string object (for both a and b, these two will point to the same object).
Class loading: String is used as arguments for class loading. If mutable, it could result in wrong class being loaded (because mutable objects change their state).

[anudeepyendrapalli]

Excellent sir.Good to see you on youtube. please do Keep posting videos like this to enjoy your lecture. 4 years back when I was a fresher I have learnt Java from you and now I am working for MNC. Thanks a lot for your dedicated teaching and inspiration.

[jvsnyc]

Watching this, I realize I once failed an interview by suggesting that a mutable object could be used as a key in a map!! The question wasn't posed in such an obvious way, I never would have gotten that wrong. While discussing a solution they asked "So, what else could we have used as a key here?" and might have suggested the mutable object as a possibility. I said "Yeah, sure" because I was nervous and wanted to get whatever else in. They had a lot of candidates and someone got to say "Yay, we just narrowed down." I really didn't realize it until just now watching this discussion. Knowing something well enough to answer a question phrased directly is different from knowing it well enough to see it and deal with it in the wild. I see how preparing one for these kinds of things that affect both ones code and interviews is being considered by these teachers.

[anandashok]

First of all the way you used toUpperCase() is wrong. It will change the value and create another object in String constant pool, but it will not return the converted value to s1. The basic String Class operation.

[karunkausal]

Hello sir Today in one interview i have said this answer for string immutable but then interviewer asked me how is it possible string introduced in java Early and hashmap introduced later. So is it possible

[hareesh]

Hi Hari Krishna,

This is a one good reasonfor String Immutability. I found few more good reasons for string immutability in StackOverflow thread.


String is immutable for several reasons, here is a summary:

Security: parameters are typically represented as String in network connections, database connection urls, usernames/passwords etc. If it were mutable, these parameters could be easily changed.
Synchronization and concurrency: making String immutable automatically makes them thread safe thereby solving the synchronization issues.

Caching: when compiler optimizes your String objects, it sees that if two objects have same value (a="test", and b="test") and thus you need only one string object (for both a and b, these two will point to the same object).

Class loading: String is used as arguments for class loading. If mutable, it could result in wrong class being loaded (because mutable objects change their state).
That being said, immutability of String only means you cannot change it using its public API. You can in fact bypass the normal API using reflection. See the answer here.

[singam]

Really it's very good nd clearly explained, thank you sir.

[arunchalla]

One small correction,


String s1 = "hk";
Hashtable ht = new Hashtable();
ht.put(s1, "1");
ht.put("Ravi", "2");
ht.put("Raju", "3");
s1.toUpperCase();
--> this should be s1 = s1.toUppercase(); to make s1 as HK


Your program has no effect on s1 as mentioned reason above.
Moreover you need to pass ht.get(s1) instead of ht.get("hk") to see if calling s1.uppercase() has really changed the value from hk to HK.


Just to make it clear, calling string methods on string value will not have affect untill you say s1 = s1.toUpperCase(); and observe that this is new object and that old object with s1 = hk is destroyed.

[manashranjan]

Thanks Sir Hari sir means Hari sir only whole team trying to convince that for pooling purpose string is immutable but Hari Krishna sir prove that why string is immutable

[amitclick]

If you try to get Object obj= ht.get("HK"); means upper case then you will get null ..it means value 1 is not created for after making it s.toUpperCase();

[lawanutech]

Hashmap uses generics HashMap<K, V>.So, keys can be of different datatype too.It is not a strong reason for String Immutability.

[adaylightsmile]

(wrong) ( not immutable 00:10:51 )
[{there actually I confused}]
in the previous diagram if the string is given as mutable
then only we get NULL
and only IM-MUTABLE WE GET 1 Value.

[{ Finally whole Explanation is GOOD }]..
:) i am here to help you by mentioning that and then concept will get helpful

[manishanker]

string class introduced in Java 1.0 where as collection are introduced in 1.2 and what is the relation ship between string class and collection

[himeshgupta]

I think string is a primitive so it should get passed by value in java( and all non- primitive obj are passed as references) and thus the map key shouldn't change.... Would be glad if you clarify me on this sir..

[prangshumaity]

Super sir.no one can teach this point.this make your students unique from other.

[girinani]

you are one of the best in Ameerpet Institutes, Nice explanation, not only explanation, also you are trying to motivate

[rajeshgupta]

Great explanation sir. Thank you sir for deep explanation

[noth]

After watching this video ...My soul is saying only one word awesome Hari

[challarajesh]

good explanation. thank u sir
please can provide the why eaquals() and hashcode() method and why override both methods

[digitallearning-]

thanku so much sir....plz make these type of videos, ..all the best sir...