Java: StringBuffer & Concatenation

Question

I'm using StringBuffer in Java to concat strings together, like so:

StringBuffer str = new StringBuffer();

str.append("string value");

I would like to know if there's a method (although I didn't find anything from a quick glance at the documentation) or some other way to add "padding".

Let me explain; every time I append something to the string, I want to add a space in the end, like so:

String foo = "string value";
str.append(foo + " ");

and I have several calls to append.. and every time, I want to add a space. Is there a way to set the object so that it will add a space automatically after each append?

EDIT --

String input
StringBuffer query = new StringBuffer();
Scanner scanner = new Scanner(System.in);
scanner.UseDelimiter("\n");

do {
   System.out.println("sql> ");

   input = scanner.next();

   if (!empty(input)) query.append(input);

   if (query.toString().trim().endsWith(";")) {
         //run query
   }
}
while (!input.equalsIgnoreCase("exit");

I'll use StringBuilder though as grom suggested, but that's how the code looks right now

can you show us some of your actual code where you are appending items? Because maybe there is another way of building the string that would make more sense. — grom, Sep 30 '08 at 08:36
hmm, I basically have a do-while loop that appends an input to a string and the loop exists when the input ends with a ";" — Jean Paul Galea, Sep 30 '08 at 08:44
It's probably more elegant (and quicker) to use a regular expression to determine whether to run the query or not, e.g.: if (query.matches(".*;\s*")) { — Chris Carruthers, Sep 30 '08 at 13:09
Wouldn't it be better to check input ends with ';' instead of converting the buffer to a string each time? — grom, Oct 01 '08 at 08:32
This might help you: http://stackoverflow.com/questions/63150/whats-the-best-way-to-build-a-string-of-delimited-items-in-java — Vinko Vrsalovic, Sep 30 '08 at 08:21

kolrie · Accepted Answer · 2008-09-30T11:51:37.817

I think this is handled easier either with a helper method (untested code):

public String myMethod() {
    StringBuilder sb = new StringBuilder();
    addToBuffer(sb, "Hello").addToBuffer("there,");
    addToBuffer(sb, "it").addToBuffer(sb, "works");
}

private StringBuilder addToBuffer(StringBuilder sb, String what) {
    return sb.append(what).append(' ');  // char is even faster here! ;)
}

Or even using a Builder pattern with a fluent interface (also untested code):

public String myMethod() {
    SBBuilder builder = new SBBuilder()
        .add("Hello").add("there")
        .add("it", "works", "just", "fine!");

    for (int i = 0; i < 10; i++) {
        builder.add("adding").add(String.valueOf(i));
    }

    System.out.println(builder.build());
}

public static class SBBuilder {
    private StringBuilder sb = new StringBuilder();

    public SBBuilder add(String... parts) {
        for (String p : parts) {
            sb.append(p).append(' '); // char is even faster here! ;)
        }
        return this;
    }

    public String build() {
        return sb.toString();
    }
}

Here's an article on the subject.

Hope it helps! :)

My pleasure. Let me know if you run into any kind of problems and I'll be glad to help! :) — kolrie, Oct 01 '08 at 15:00

score 6 · Answer 2 · answered Sep 30 '08 at 08:34

6

You should be using StringBuilder.

Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.

answered Sep 30 '08 at 08:34

grom

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score 4 · Answer 3 · answered Sep 30 '08 at 08:22

4

StringBuffer is final. You cannot derive from it. The Best solution really is to add the padding for yourself. Write a method for it and use a PADDING-Constant so that you can easily change it, or better put it in a parameter.

answered Sep 30 '08 at 08:22

Dimo

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1

David Webb · Answer 4 · 2008-09-30T08:37:48.237

3

Can you not create a new class which wraps around StringBuffer and add an appendWithTrailingSpace() method?

CustomStringBuffer str = new CustomStringBuffer();
str.appendWithTrailingSpace("string value");

(Although you may want to call your method something a little shorter.)

edited Sep 30 '08 at 08:37

answered Sep 30 '08 at 08:20

David Webb

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That should not be possible. StringBuffer is final, i.e. no derivation from it. – Burkhard Sep 30 '08 at 08:33
How does an incorrect answer get accepted and worse upvoted? Its not possible to subclass StringBuffer – grom Sep 30 '08 at 08:37
Whoops. You're right. I've changed the answer to read "wraps around" rather than "extends". Sadly it's not as neat this way. – David Webb Sep 30 '08 at 08:38
I actually think that wrapping the string buffer is just fine. Subclassing is not really appropriate in this case - you are really creating a 'builder' object using composition. Nothing wrong with it, and if the decide later to use a different implementation you can... – Kevin Day Oct 01 '08 at 03:52

score 2 · Answer 5 · answered Sep 30 '08 at 08:15

2

Just add the space yourself, it's easy enough, as per your own example.

answered Sep 30 '08 at 08:15

Johan

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yeah it's easy, but I find it dirty. And if I happen to change my mind and instead of a space, I want some other character, I'd have to go through several lines instead of one! – Jean Paul Galea Sep 30 '08 at 08:18
although yeah, I could do this: String bar = " "; str.append(foo + bar); but still I want to find out if there's a better way of doing it – Jean Paul Galea Sep 30 '08 at 08:19

score 1 · Answer 6 · answered Sep 30 '08 at 08:44

Another possibility is that StringBuilder objects return themselves when you call append, meaning you can do:

str.append("string value").append(" ");

Not quite as slick, but it is probably an easier solution than the + " " method.

Another possibility is to build a wrapper class, like PaddedStringBuilder, that provides the same methods but applies the padding you want, since you can't inherit.

Java: StringBuffer & Concatenation

6 Answers6

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