How to clone() StringBuilder

Question

Is there some ways how I could clone StringBuilder ? I am reading files by bits then convert these bits to ASCII chars after that I collect chars into String builder and when I have for example 8 chars I put that String Builder object into Array List. Then I clean it and again do the same. However I can't create new string builder because of memory and I can't do changes to that String builder because in Array List also that builder changes.

So I think I have to clone that String Builder and put it into Array List. There is just one problem String Builder don't have clone(). So what is my alternatives ?

Maybe someone could give some ideas what is neat way to do this considering about performance and memory.

ArrayList characters = new ArrayList(); int counter = 0;

StringBuilder sb = new StringBuilder(blockSize-1);

while (mbb.hasRemaining()) {   

char charAscii = (char)mbb.get();


    counter++;
    charCounter++;

     if (counter == blockSize){

        sb.append(charAscii);
        characters.add(sb);//sb.toString()
        sb.delete(0, sb.length());
        counter = 0;

    }else{

        sb.append(charAscii);

     }

 if(!mbb.hasRemaining()){
    characters.add(sb);
}



}
fc.close();
return characters;

"i can't create new string builder because of memory" - a cloned StringBuilder will use a similar amount of memory, so how would this help you? — DNA, Mar 01 '12 at 19:15
`new StringBuilder(oldbuilder.toString())` is the simplest way to copy a StringBuilder. You haven't actualy explained what you are trying to achieve, so you might be able to just store the String from the StringBuilder instead. — DNA, Mar 01 '12 at 19:17
Yap understood that it won't help anyway. So i am out of options becouse this characters.add(new StringBuilder(sb)); gives java outOffMemory exception — Streetboy, Mar 01 '12 at 19:30

Louis Wasserman · Accepted Answer · 2012-03-01T19:43:46.567

26

If you don't have the memory to create a new StringBuilder, then you don't have the memory to create a new StringBuilder, and cloning wouldn't change that. The only real way to copy a StringBuilder is new StringBuilder(myBuilder), or something equivalent.

If you're getting OutOfMemoryException, you'll need to either get more memory, or find some other way to reduce memory consumption.

edited Mar 01 '12 at 19:43

answered Mar 01 '12 at 19:16

Louis Wasserman

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It should be noted that this OutOfMemoryException doesn't mean the machine is out of memory, it means the JVM has hit its limit. It may be a machine limit or a JVM limit. I would recommend making sure you are telling Java to use enough memoryby passing in e.g. `-Xmx1024` – SubJunk Apr 06 '20 at 02:49

score 1 · Answer 2 · answered Mar 01 '12 at 19:26

1

You can clear StringBuilder object by:

1.

sb.delete(0, sb.length())

2.

sb = null;
sb = new StringBuilder();

For performance, 1. is the better option. But you cannot clone it anyway. For more info about clone see

answered Mar 01 '12 at 19:26

Tapas Bose

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In 2. `sb = null;` isn't necessary since `sb = new StringBuilder();` also overwrites `sb`. Also, I would think 1 may immediately impact memory consumption since it modifies the object, whereas 2 just changes what a variable points to, leaving any original object still in memory as a possibly candidate for garbage collection. – coder34 Jun 04 '22 at 15:38
@LoganMay, I think 1) will make the previously allocated memory eligible for the garbage collection. – Tapas Bose Jun 12 '22 at 06:34
I agree that seems possible in theory. Is there any documentation you can point to that makes it explicitly clear whether the memory affected by the `delete` call is immediately freed or first has to be garbage collected? – coder34 Jun 20 '22 at 15:22

How to clone() StringBuilder

2 Answers2