Why String is Immutable ?

[Karn Kumar]

Hi All ,


Can anybody explain why string is immutable ? or what are it's advantage ?


Thanks..

Regards,
Chetan

[Jeff Verdegan]

Please SearchFirst

Why is String immutable?

[Winston Gutkowski]

Chetan Dorle wrote:Can anybody explain why string is immutable ? or what are it's advantage ?

I'm afraid the answer is recursive: it's main advantage is that is it is immutable; and that, I suspect is why they made it so.

Just one advantage of immutable objects is that, in Java terms, they are Thread-safe; so you can pass a String around a multi-threaded environment with no worries.

Winston

[Seetharaman Venkatasamy]

Winston Gutkowski wrote:
Just one advantage of immutable objects is that, in Java terms, they are Thread-safe; so you can pass a String around a multi-threaded environment with no worries.

Indeed

[Randall Twede]

indeed

i recently tried to pass an exception around. i quickly decided to pass a string instead.

[Jeff Verdegan]

Randall Twede wrote:indeed

i recently tried to pass an exception around. i quickly decided to pass a string instead.

Color me confused.

Your code was modifying that Exception? In a multithreaded context? And you changed it to use a String instead?

Why not just not modify the Exception?

And it seems odd that your semantics are such that Exception and String are both appropriate to use in the same context.

[Randall Twede]

this should clarify. this is from actionPerformed(). originally i passed a reference to the exception(e) to model. i changed it to pass the string.

            String strID = e.getActionCommand();

            else if(strID.equals(Constants.BEGIN))
            {
		view.changeButtons();
            	view.setMessage(model.getMessage(Constants.BEGIN));
            }

[Jeff Verdegan]

Randall Twede wrote:this should clarify

Not one bit. I don't do GUIs, and have no idea how Exception vs. String comes into play here.

Don't worry about it though.

[Randall Twede]

well, i am not sure why but it didn't work when i passed the exception and it works now
anyway, i was just agreeing that being immutable isn't a bad thing

[Jeff Verdegan]

Randall Twede wrote:well, i am not sure why but it didn't work when i passed the exception and it works now

Depending on what you mean by "didn't work," it's highly unlikely that it has anything to do with mutability.

[Randall Twede]

ok, this is way off topic but:
i had this comparison which i did in actionPerformed() and it entered the if. when i passed the exception to model and did the exact same comparison it did not execute the code in the if.

if(((JButton)e.getSource()).getText().equals("Begin"))

maybe i should just stay off the internet when i have been drinking

[Jeff Verdegan]

Randall Twede wrote:ok, this is way off topic but:
i had this comparison which i did in actionPerformed() and it entered the if. when i passed the exception to model and did the exact same comparison it did not execute the code in the if.

if(((JButton)e.getSource()).getText().equals("Begin"))

Still no idea what you're saying here, but I'm sure it has nothing to do with immutability. If you want to investigate it further, you can start a new thread or PM me, but I think we should let this tangent die in this thread now.

[Seetharaman Venkatasamy]

Jeff Verdegan wrote:If you want to investigate it further, you can start a new thread or PM me

Please here ...

[Jeff Verdegan]

Seetharaman Venkatasamy wrote:

Jeff Verdegan wrote:If you want to investigate it further, you can start a new thread or PM me

Please here ...

No. Let's not pollute this thread with any more off-topic discussion. Just start your own thread.

[Winston Gutkowski]

Jeff Verdegan wrote:No. Let's not pollute this thread with any more off-topic discussion. Just start your own thread.

Actually, I think what Seetharaman was saying is that PM's are best kept for truly private stuff (he is a Rancher; which I believe is a form of moderator). But I agree, t'other discussion maybe best in another thread.

Winston

[Bear Bibeault]

Winston Gutkowski wrote:he is a Rancher; which I believe is a form of moderator

Nope. It's a title administered just because one of the staffers felt like it.

[Seetharaman Venkatasamy]

Randall Twede wrote:maybe i should just stay off the internet when i have been drinking

we are surrounded by bartenders!

[Campbell Ritchie]

Seetharaman Venkatasamy wrote: . . . we are surrounded by bartenders!

But they may have suffered like the little man who used to grace the top of all JavaRanch pages

[Karn Kumar]

Hi Guys,

We are out of topic but anyways ....Thanks for your replies.


Hi Bear , Can you explain the hierarchy in the forum also ?

[Campbell Ritchie]

Bears outrank lions.

[Jeff Verdegan]

Campbell Ritchie wrote:Bears outrank lions.

Packers outrank both.

[Winston Gutkowski]

Jeff Verdegan wrote:Packers outrank both.

And Vikings'll burn the lot of yaz...and take your women.

Winston

[Raj Kuppala]

Winston Gutkowski wrote:

Chetan Dorle wrote:Can anybody explain why string is immutable ? or what are it's advantage ?

I'm afraid the answer is recursive: it's main advantage is that is it is immutable; and that, I suspect is why they made it so.

Just one advantage of immutable objects is that, in Java terms, they are Thread-safe; so you can pass a String around a multi-threaded environment with no worries.

Winston

Hi Winston,
I have a doubt about that i think "Thread-safe" in the sense it is synchronized. When i wrote a program with String it is allowing multiple threads to change the content of it,but as it is thread-safe it should not allow to modify it.. But "String Buffer" is not allowing multiple threads at a time to modify it.. So now which one is thread-safe ? Its my doubt..


Which is thread-safe among String and StringBuffer

[Winston Gutkowski]

Raj Kuppala wrote:Hi Winston,
I have a doubt about that i think "Thread-safe" in the sense it is synchronized. When i wrote a program with String it is allowing multiple threads to change the content of it...

No it isn't. You can't, in the normal scheme of things, change a String; the only thing you can do is replace it with a different value. And if the value is passed as a parameter, any replacement will only affect the parameter itself, not the value it came from.

But, in answer to your last question (and depending on what your criteria are for "Thread-safe"): both, since StringBuffer is synchronized.
However, given the choice, I would always pass around a String rather than a StringBuffer, and I would generally use StringBuilder rather than StringBuffer.

Winston

[Steve Luke]

You should also note that StringBuffer being synchronized really only helps you in that multiple threads can modify the StringBuffer safely, however, the value of the StringBuffer can be modified out from underneath you in one thread in unexpected ways. For example, let's say you have this code:

StringBuffer theString = new StringBuffer("Hello There");

public StringBuffer getTheString()
{
    rerurn theString;
}


public void runsInThreadA() {
  StringBuffer data = getTheString();

  int startOfSection = data.indexOf("lo");
  String showMe = data.substring(startOfSection, 5);
  System.out.println(showMe);
}

You might expect it to be pretty save that the output should print "lo Th", the 5 characters starting at where "lo" was founds. But that is not a sure thing if another Thread is modifying the StringBuffer at the same time. For example, if another Thread runs:

public void runsInThreadB() {
  StringBuffer data = getTheString();

  data.deleteCharAt(1);
}

If this code gets run at just the right time, between the indexOf() and substring() calls in the previous code, the output would be unexpected. To prevent this sort of thing you would have to add additional synchronization:

public void runsInThreadA() {
  StringBuffer data = getTheString();

  synchronize(data) {
    int startOfSection = data.indexOf("lo");
    String showMe = data.substring(startOfSection, 5);
    System.out.println(showMe);
  }
}

You do not have to worry about this sort of thing with String, since the String itself can't be changed - and therefore can't be changed out from under you in this way, and doesn't require additional synchronization.

[Jeff Verdegan]

Raj Kuppala wrote:

Winston Gutkowski wrote:

Chetan Dorle wrote:Can anybody explain why string is immutable ? or what are it's advantage ?

I'm afraid the answer is recursive: it's main advantage is that is it is immutable; and that, I suspect is why they made it so.

Just one advantage of immutable objects is that, in Java terms, they are Thread-safe; so you can pass a String around a multi-threaded environment with no worries.

Winston

Hi Winston,
I have a doubt about that i think "Thread-safe" in the sense it is synchronized.

Synchronization is not necessary to make an immutable class threadsafe. However, you can still use a threadsafe immutable class in a thread-unsafe manner.

When i wrote a program with String it is allowing multiple threads to change the content

No, it didn't. You cannot change the contents of a String because String is immutable, regardless of how many threads you have.