StringBuilder from String in Java

Question

Assume that we have a StringBuilder or StringBuffer like below:

StringBuilder s1 = new StringBuilder("xxx");
StringBuffer s2 = new StringBuffer("xxx");

We can get a String from the above variables using the toString() method.

I know that toString is an over-ridden method in both classes.

Assume also that we have a String like below:

String s3 = "xxx";

I can't get a StringBuilder or StringBuffer using toStringBuilder() or toStringBuffer(). Instead, the way we can achieve is like below:

StringBuilder sb = new StringBuilder(s3);

Is there a reason why toStringBuilder()/toStringBuffer() is not defined and is there any other effective way to get a StringBuilder/StringBuffer from String.

What benefit would there be, in your view? What do you dislike about calling new StringBuilder(s)? — Jon Skeet
– Jon Skeet, Commented Jun 6, 2014 at 12:17
A mutable StringBuilder wraps an immutable String, so why do you want to get a wrapping instance where a String doesn't even have to know, that something like a StringBuilder exists? — Smutje
– Smutje, Commented Jun 6, 2014 at 12:17
If you're using Scala you can create an implicit class over the java.lang.String class and create your own .toStringBuilder() method. — Konstantin Yovkov
– Konstantin Yovkov, Commented Jun 6, 2014 at 12:18
@JonSkeet : i am just checking the reason why they have not given the same method what they have given in case of stringbuilder class — Karibasappa G C
– Karibasappa G C, Commented Jun 6, 2014 at 12:36

Joop Eggen · Accepted Answer · 2014-06-06 12:19:23Z

2

String itself is immutable. That has many advantages, especially with concurrent usage, sharing substrings and such.

Also back and forth coupling between classes is bad design.

answered Jun 6, 2014 at 12:19

Joop Eggen

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5 Comments

The Archetypal Paul Over a year ago

"String itself is immutable". Yes it is. But what's that got to do with the question? .toStringBuilder would not modify the String but make a new StringBuilder with the same content.

Karibasappa G C Over a year ago

i have same question like Paul ...and coupling is already done in case of stringbuilder.toString();

Jon Skeet Over a year ago

@KaribasappaGC: No, there isn't two-way coupling. StringBuilder "knows about" String, but the String API doesn't know about StringBuilder at all.

Joop Eggen Over a year ago

@Paul yes, there my argumentation is unclear. I meant more or less that a StringBuilder won't back its data to the String. Or so.

The Archetypal Paul Over a year ago

Well,it might. As long as it doesn't modify it, there's no particular reason why StringBuilder shouldn't refer to the original string as its initial contents. It would make (new StringBuilder("Foo")).toString quite efficient :)

Ivaylo Strandjev · Accepted Answer · 2014-06-06 12:18:23Z

0

toString is a method that is part of the Object class and thus all classes of java will have such method. A String is immutable and as such both toStringBuilder and toStringBuffer will create new objects. I think that if there were such methods many users would be mislead that using these methods they can modify the string in-place. Also because of the same reasons there can not possible be any more efficient way to create a StringBuilder/StringBuffer.

answered Jun 6, 2014 at 12:18

Ivaylo Strandjev

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1 Comment

The Archetypal Paul Over a year ago

"many users would be mislead that using these methods they can modify the string in-place" Really? Do people really think .toString modifies the actual content of the StringBuilder, rather than making a new String out of it?

laune · Accepted Answer · 2014-06-06 12:20:39Z

0

You might ask for a considerable number of String.toFoo() methods, and where to draw the line? You can construct StringBuilder and StringBuffer using the constructor. That's enough - why add another method?

answered Jun 6, 2014 at 12:20

laune

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2 Comments

Karibasappa G C Over a year ago

we usually do lot of conversions between string and string buffer and string builder..atleast in my experience...so this question comes..its not on any user defined class like Foo

laune Over a year ago

You have the StringBu*er constructors - why should String be burdened with more methods? What would it achieve? Why would code be better that way?

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