StringBuffer
I have read that strings are immutable and it is therefore inefficient to change their contents by doing something such as String string = new String("Hey!") and then attempting to reassign it a new value by doing something like string = "wassup?". I have read that the proper way to do this is to use a StringBuffer, which I have no problem with, except that in the app I am writing I need to assign the value in a string into a label over and over again with different values, which I have been doing currently as label.setText(string) and I haven't found a way yet to do the same thing using a StringBuffer. Am I missing something or is it not possible to assign the value of a StringBuffer to a JLabel? Thanks in advance.
[733 byte] By [
ugga24a] at [2007-10-1 1:31:55]
You're missing a couple of key concepts, and misunderstanding what you heard about Strings.
First, you should never need to use an explicit constuctor for Strings. String s1 = "abc";
Stirng s2 = new String("abc");
Both of the above do almost the same thing. The second one does create a new String object, and is less efficient, but that's miniscule. The main thing is that the second one is non-standard, harder to read, and adds no value.
> I have read that strings are immutable and it is
> therefore inefficient to change their contents by
> doing something such as String string = new
> String("Hey!") and then attempting to reassign it a
> new value by doing something like string = "wassup?".
Not quite. String's immutability means you can't change a String's contents.
String str = "abc";
str = "xyz";
str = foo.getName():
All of the above str = just stuff a reference value--a "pointer" to an object--into str.
> I have read that the proper way to do this is to use
> e a StringBuffer,
That's different.
String str s1 = "a" + foo.getSomething() + "b" + bar.getSometing(); // good
// bad, but see *** below
String s2 = "a";
s2 += foo.getSomething();
s2 += "b";
s2 += bar.getSomething();
// good
StringBuffer sb = new StringBuffer();
sb.append("a");
sb.append(foo.getSomething());
sb.append("b");
sb.append(bar.getSomething());
String s3 = sb.toString(); [/code]
***s2 is "bad" because each time you do s2 += whatever you're creating a StringBuffer, stuffing in the original s2, appending the other part, then creating a new String. You'd have to do a lot of it to make a noticeable difference.
Still, s3's append() would be better. But in that case, you could just go with s1 anyway.
The case where it would really make a difference would be in a loop where you don't have a fixed set of strings to put together at compile time, and the number could potentially get large.
s1 is fine because the compiler turns it into a bunch of calls to sb.append anyway, and the only String object created at runtime is the final result.
> which I have no problem with,
> except that in the app I am writing I need to assign
> the value in a string into a label over and over
> again with different values, which I have been doing
> currently as label.setText(string) and I haven't
> found a way yet to do the same thing using a
> StringBuffer.
You don't need to. Calling setText just copies the reference--a 4-byte value--so that the label's text property is pointing at the same string as the reference you pass in. It doesn't create a new string each time. (Well, it shouldn't. It's possible that the implementor of setText did something stupid like calling new String() on the parameter that's passed, but I doubt it.)
> Am I missing something
Several things, actually. :-)
> or is it not
> possible to assign the value of a StringBuffer to a
> JLabel?
If there's no method with that signature, then it's not possible. It's also not necessary, nor would it be beneficial if it were possible.
