Does StringBuilder need ToString()

Question

This should hopefully be a quick one. I have a StringBuilder like so:

StringBuilder sb = new StringBuilder();

I append to my StringBuilder like so:

sb.Append("Foo");
sb.Append("Bar");

I then want to make this equal to a string variable. Do I do this like so:

string foobar = sb;

Or like so:

string foobar = sb.ToString();

Is the former being lazy or the latter adding more code than is necessary?

Thanks

Cupellation

Apologies, thought the same principles applied to both! – Cupellation

What's lazy is you couldn't just try both and see that one doesn't work -1 – Archie

To be fair I asked because I was using a StreamWriter and noticed it worked with or without .ToString(), I didn't think that this might be an overload of the StreamWriter method – Cupellation

I see, well in that case leave the ToString() off when calling. At worst the overload will call it for you and at best it might have some clever optimisation. But either way the language designers added the overload for your benefit, so might as well use it. – Archie

You cant implicitly convert from StreamWriter to a string either. And calling .ToString() wont give you the content of the writer. – Pericranium

@Pericranium he means he is calling the StreamWriter.Write(object value) method. With a StringBuilder as his value. – Archie

I personally would have preferred if the compiler just worked the conversion magic behind the scenes, but that wasn't what was done. I suppose purists wouldn't want to do subtle behind-the-scenes-conversions, although having to convert 'cat' to 'cat' seems overboard to me! Also, despite this question seeming simplistic, it actually has brought forth a lot of good discussion anyway. – Martica

Answer 1

In Java, you can't define implicit conversions between types anyway, beyond what's in the specification - so you can't convert from StringBuilder to String anyway; you have to call toString().

In C# there could be an implicit user-defined conversion between StringBuilder and String (defined in either StringBuilder or String), but there isn't - so you still have to call ToString().

In both cases you will get a compile-time error if you don't call the relevant method.

Gametocyte

Answer 2

In C# you need to use string foobar = sb.ToString(); or you will get an error: Cannot implicitly convert type 'System.Text.StringBuilder' to 'string'

Ceresin

Answer 3

In Java, string foobar = sb; won't compile. You have to use String foobar = stringBuilder.toString();

Powerdive

Answer 4

You could have tested it before asking... You would have seen that

string foobar = sb;

doesn't compile (C#).

Use sb.ToString().

Ambrosial

Answer 5

String foobar = sb.ToString();

should be used. As this will convert the StringBuilder to String and then assign the value.

Using string foobar = sb; will give you a compile time error "Cannot implicitly convert type to "

Blowbyblow

Answer 6

Previous answers are correct, just to clarify some things. StringBuilder is not a String's subclass so you can't cast from StringBuilder to String. StringBuilder's toString() method produces a String object, so you should use it to "cast" from StringBuilder to String. Hope this helps.

Nogood

Answer 7

When converting to String use toString in Java. (ToString in C#)

Inscrutable

Answer 8

ToString() in StringBuilder required to convert to String.

String str=sb.toString();

Chaps

Answer 9

In Java all objects have toString(), inherited from Object superclass. StringBuilder (SB) is mutable, String is not. Assigning SB (Mutable) to String (immutable) needs to copy the internal char buffer and return an immutable String instance.

Quadroon

Answer 10

All previous answers are correct. However, wanted to highlight another usage, which, in some scenarios can be useful. When converting to string we can use built-in static functions/utilities e.g.

C#

string str = Convert.ToString(sb);

Java

String str = String.valueOf(sb);

This is particularly useful when input "sb" can be null, but, code wants to handle it gracefully without raising a NullPointerException and avoids code like:

if (sb == null) 
   return "null";
else
   return sb.toString()

Quadroon