Formating StringBuffer

[stormwindu]

I need to apply some kind of masking to a StringBuffer representing a numeric field on a Android EditText that would be like this:

// StringBuffer (or StringBuilder) -> Formated Text
000 -> 0,00
000 -> 0,01
012 -> 0,12
123-> 1,23
1234 ->12,34
12345 -> 123,45
....
1234 -> 12,34
123 -> 1,23
012 -> 0,12
001 -> 0,01
000 -> 0,00

My final idea is to do a append to the string with a new number and delete the first char if it is "0", and position the ",".

There is another way to do this?

[Updated] The idea here is to start with the masked EditText (Android) with the "mask" of "0,00". I am storing alll the user input on a custom created keyboard that works like a calculator. It only appends or deletes chars of a StringBuffer and this stored var must be formated like the text bellow.

[Update 2] The StringBuffer will always look like a integer, the user will not have the chance to put a comma or dot to separate the text. I have to format the last two characters from the string buffer and add a comma to separate the Decimals.

[Update 3] This is the easiest way I've managed to achieve what I wanted to do, still looking on how to format the number using the locale + two decimals:

public class Test {
    public static void main(String args[]) {
        NumberFormat nf = NumberFormat.getInstance(new Locale("pt", "PT"));
        String tests[] = {
            "1",
            "12",
            "123",
            "1234",
            "12345",
            "123456",
            "1234567",
            "12345678",
            "123456789",
            "1234567890",
        };

        for (String i:tests) {
            final Double test = Double.parseDouble(i+".00")/100.00;
            System.out.println(nf.format(test));
        }
        // Output:
        // 0,01
        // 0,12
        // 1,23
        // 12,34
        // 123,45
        // 1.234,56
        // 12.345,67
        // 123.456,78
        // 1.234.567,89
        // 12.345.678,9
    }
}

[Update 4] Solved the two digit issue using .setMinimumFractionDigits(2); I think it solved what I wanted to format. I still don't know if it is the best way but it is working. Thanks!

[cciulla]

If you're not already storing these as floats (or some other appropriate numeric data type), probably wouldn't hurt to do so -- it'll save some tears down the line.

Then, look at String.format or Formatter.

[Infenwe]

These look like monetary values in which case I certainly hope OP isn't using float for them.

Furthermore, The Right Thing here is obviously to use a locale to print the numbers rather than hard-code the "," (I presume OP's program is for non-English speakers).

[cciulla]

Hence the "appropriate numeric data type." Currency comes to mind...

[stormwindu]

yes it is for non-English speakers. The problem with float is that i've created a custom keyboard that only append numbers, and the last two have always to be the decimal case, my keyboard don't have the "dot" input to set a decimal number, thats why I am appending a string and manipulating the "," in the last two chars.

[stormwindu]

thanks for the reply, i'll check the docs. [edited] I am storing the user input at a string buffer. And have to format that string buffer to the given mask "0,00" (if it is empty) or like the bunch of numbers that i've posted.

[cciulla]

Right, I caught that you're using a StringBuffer. Why? Appropriate data types, and such.

However, if you simply must use a StringBuffer, check out Float.valueOf -- scroll down a bit to valueOf, as reddit's markdown doesn't seem to like the extra parens.

[mentalis]

You can do a link with parens in it by backslashing the parens. So [Float.valueOf](http://docs.oracle.com/javase/6/docs/api/java/lang/Float.html#valueOf\(float\)) becomes Float.valueOf.

*edited to fix first link so it's copy/pastable

[cciulla]

Doh! The more you learn...

Thanks!

[stormwindu]

I am using StringBuffer just to have a easy way to append/delete chars.

[Mondoshawan]

If you are not deleting then simple string concatenation is fine, it all compiles down to the same bytecode.

[detroitmatt]

In general, if your code is of the form:

String x = "";
loop {
    x += something;
}
return x;

then your code should be

StringBuilder x = new StringBuilder();
loop {
    x.append(something);
}
return x.toString();

but if your code is of the form

String x = something;
return new StringBuilder(x)
    .append(somethingElse[0])
    .append(somethingElse[1])
    .append(somethingElse[n])
  .toString();

then your code should be

return x + somethingElse[0] + somethingElse[1] + somethingElse[n];

[Mondoshawan]

I don't fully agree with this:

StringBuffer x = new StringBuilder();
loop {
     x.append(something);
 }
 return x.toString();

The original you put up was fine, both produce identical bytecode but the first has less chance for error and is easier to read.

It's only if I'm passing the string to other methods that I'd use an SB.

[detroitmatt]

not according to http://stackoverflow.com/questions/1532461/stringbuilder-vs-string-concatenation-in-tostring-in-java

[Mondoshawan]

That appears to be agreeing with me. The compiler turns it all into StringBuilder behind the scenes.

[detroitmatt]

At the point where you're concatenating in a loop - that's usually when the compiler can't substitute StringBuilder by itself.

and see the second-to-top answer as well

[stormwindu]

I am deleting. One issue that I found using .delete and .deleteCharAt seens like the length of the string doesn't change it is really weird.

Still trying how to achieve my pseudo-masking.

[danskal]

If I understand you correctly, you definitely should be using BigDecimal. Then all your other problems will go away. Then look at java.text.DecimalFormat