Why does a `StringBuilder`have a method `append` but no meth

Question

Why does a `StringBuilder`have a method `append` but no method `prepend` that does not make much sense to me Anyone knows why there s none

Ruckus · Answer

Because you can use `insert 0 ` or any other index for that matter

alex · Answer

There is `Insert` <https docs oracle com javase 7 docs api java lang StringBuilder html insert int 20java lang String > But yeah maybe there should be some sugar Keep in mind that prepending is expensive operation unlike appending

Robert · Answer

There is none but that s probably because I am doing MPP disappointed

Robert · Answer

<https kotlinlang org api latest jvm stdlib kotlin text string builder index html> there seems to be no `insert` for other than native

alex · Answer

It s also available for JVM `typealias StringBuilder = StringBuilder`

alex · Answer

but yes nothing else except JVM and native

Robert · Answer

I ll give it a try in < C3PQML5NU|multiplatform> Tyvm

kd · Answer

You can probably write an extension function if you plan to use prepend a lot

Robert · Answer

< kd> IntelliJ suggested that but I can only do that in the files itself so the dependencies which are read only disappointed

Dico · Answer

It s because it would be very inefficient implementation wise to support it

Dico · Answer

The most common use case of StringBuilder is to avoid concatenation of many strings creating many intermediate steps

Dico · Answer

It s most efficient to put them in an array from left to right and not have to move them around

Jay · Answer

There s no reason why a circular buffer can t be used which means prepending or appending should both be equally cheap operations Only inserting in the middle would be expensive Even if it s not implemented that way currently the performance cost of a specific implementation should not be a good reason to cripple an API design

Dico · Answer

StringBuilder just isn t intended to be used like that You can do it though with insert The vast majority of use cases can simply be expressed using appends which makes it a StringBuilder not a CharacterList For a silly analogy you don t move half of a house over after you ve built it to make space for the other

Dico · Answer

It s just a buffer that has improved repeated concatenation performance because it is not required to be immutable

Robert · Answer

gt StringBuilder just isn t intended to be used like that How do you figure gt You can do it though with insert Problem is there is no insert gt For a silly analogy you don t move half of a house over after you ve built it to make space for the other That s a strange analogy imho which is not about the use case we want to prepend that s not the discussion If the implementation for insert prepend is to move the house then maybe the implementation is inefficient but I agree with < Jay> that it is strange to leave it out because of that What about reverse + append + reverse Even more inefficient I d think

Dico · Answer

There is insert

Dico · Answer

I agree that they could have made the implementation such that operations other than append and replace would theoretically perform a bit better

Dico · Answer

But what I m saying is I think they didn t because it is not the target use case

Dico · Answer

If you re in a situation when you need such control of a String you re making and the performance of insert is too bad it might be a good idea to make a StringBuilder that is tailored to your use case

Dico · Answer

insert method <http hg openjdk java net jdk8 jdk8 jdk file 687fd7c7986d src share classes java lang StringBuilder java l281>