Parsing number with negative suffix

Question

Can someone explain to me why the below code gives this output?

1.2
null

Running the following code:

String positive = "1.2+";
String negative = "1.2-";
DecimalFormat format = new DecimalFormat("0.0");
format.setPositiveSuffix("+");
format.setNegativeSuffix("-");  
format.setDecimalFormatSymbols(DecimalFormatSymbols.getInstance(Locale.US));
System.out.println(format.parse(positive, new ParsePosition(0)));
System.out.println(format.parse(negative, new ParsePosition(0)));

This works though, but I do not like the repetition of the pattern:

String positive = "1.2+";
String negative = "1.2-";
DecimalFormat format = new DecimalFormat("0.0+;0.0-");  
format.setDecimalFormatSymbols(DecimalFormatSymbols.getInstance(Locale.US));
System.out.println(format.parse(positive, new ParsePosition(0)));
System.out.println(format.parse(negative, new ParsePosition(0)));

Is the suffix not intended to be used for parsing?

Stepsister

parse is not guaranteed to consume the whole string. It will stop when it gets a character it doesn't know what to do with. – Jury

@PeterLawrey I know, but I thought I told it what to do when I set the suffix? And why does it handles + but not -? – Stepsister

@PeterLawrey I would also assume that the second code is slower, as it would need to parse the whole string twice? – Stepsister

I have to admit, I have never seen suffixes used. Perhaps its behaviour isn't what you want. – Jury

@PeterLawrey Me neither. And googling for it yielded very little result. And the javadocs is useless to say the least. Thus my note in the end: is it not even used for parsing? Odd that I cannot find any documentation at all – Stepsister

For the record, setting a negative PREfix works correctly with your code. I checked the API and it is near worthless. I say either just use the negative prefix or go a different route. – Angi

@ConorSherman The problem is that I have no control over the input. – Stepsister

Could you strip off the last character from the input string, parse the remaining digits with something like Integer.parseInt(input), and then multiply by -1 if the last character was a '-'? – Angi

@ConorSherman I could do that. But my second code that works is cleaner. My main question is why I get the results I get – Stepsister

Answer 1

As specified in the javadoc :

The negative subpattern is optional; if absent, then the positive subpattern prefixed with the localized minus sign ('-' in most locales)

In your exemple, the parser is waiting "-1.2-", so you have to add this line :

format.setNegativePrefix("");

Have a nice day !

Forwardness

Did you try that code? I tried it as well before posting, did not work tho – Stepsister