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Joel on Software

.NET Strings question

In .NET (and Java), Strings are immutable. So any operations such as string.replace will not change the string object but will create a new object in the pool.

If you had a String s, and fill that with the content of a text document, and then call s.replace("\n", " "), will that create one new string in the pool or will it create as many as there are newlines?

Will a StringBuilder provide a better solution in this instance?

Wednesday, February 25, 2004

Ask yourself: would they have even provided this method if the performance was so terrible that you'd be forced to avoid it and do it yourself?

Brad Wilson (
Wednesday, February 25, 2004

The StringBuilder class is useful whenever you are going to be modifying strings a lot. For example, if you had a loop statement and you wanted to append a character to the end of a string every iteration, you would use a StringBuilder.

The primary difference is that operations that appear to modify a String object (like replace) actually are creating a new string object and returning that.

So I would say if you were just calling Replace() at the end of your method, then you should be fine performance-wise. However, if you were looping through your document line by line to build the string, you would want a StringBuilder.

And newlines and the String object are not related. A String object is a "sequential collection of System.Char objects that represents a string"

See for more info.

Wednesday, February 25, 2004

There is a very useful chapter on "Improving Managed Code Performance" available to download from:

It covers strings operations in .NET amonst other things.

A sample:
"When working with strings, consider the following recommendations:
    Avoid inefficient string concatenation
    Use + when the number of appends is known
    Use StringBuilder when the number of appends is unknown
    Treat StringBuilder as a reusable buffer
    Compare string references where possible
    Use String.Intern when comparing strings multiple times in your application"

Thursday, February 26, 2004

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