How do I parse ANY Number type from a String in Java?

Question

I'm aware of the methods like Integer.parseInt(myString) and Double.parseDouble(myString) but what I optimally want is a method like Number.parseNumber(myString) which doesn't exist. How can I achieve that behaviour in another way? (I want the parsed Number to reflect the String "exactly" in terms of for example number of decimals).

Example:

"0" => Number (internally of Integer subclass)

"0.0" => Number (internally of Double subclass)

Also, no ugliness like checking for decimal separators etc.

new BigDecimal(yourString). That should give you a Number representing the value of the string. (If you say but I want it as a double if it's "0.0" and as an int if it's "0", I don't really understand how you would expect it to work. What type would the variable have, that you want to store the result in?) — aioobe
– aioobe, Commented Oct 8, 2015 at 14:11
In general, you can't. Method overloading does not allow you to mix return types. — Phylogenesis
– Phylogenesis, Commented Oct 8, 2015 at 14:13
Just to clarify... Float, Double, Integer Long etc. all extend the Number superclass, which is abstract but I can still have a variable of that type. I expect it to return a Number that is internally any of those classes — Joakim
– Joakim, Commented Oct 8, 2015 at 14:15
Do you want it to use the smallest type that fits? E.g. "1024" fits Short, Integer and Long. Ideally, I'm guessing you'd want it to return Short. — Erick G. Hagstrom
– Erick G. Hagstrom, Commented Oct 8, 2015 at 14:25
True. It doesn't really matter but I'd want it to return the most suitable subclass. — Joakim
– Joakim, Commented Oct 8, 2015 at 14:29

Joakim · Accepted Answer · 2015-10-08 14:16:38Z

8

Number number = NumberFormat.getInstance().parse(myString);

Seems to do the trick...

answered Oct 8, 2015 at 14:16

Joakim

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8 Comments

Erick G. Hagstrom Over a year ago

Only returns Long and Double. Not quite what you asked for originally.

Joakim Over a year ago

I don't see that in the documentation, but it is sufficient for my needs. And yes, it is "quite" what I asked for.

Erick G. Hagstrom Over a year ago

Here's the link to the JavaDoc. docs.oracle.com/javase/8/docs/api/java/text/… (Notice that the details for parse(String) refer one to the details for parse(String, ParsePosition) for additional information.

Erick G. Hagstrom Over a year ago

And I misunderstood. I took your question to be about any subtype of Number, including BigInteger and BigDecimal, since you require " the parsed Number to reflect the String exactly in terms of for example number of decimals".

Phylogenesis Over a year ago

And even if this is what you wanted, it's worth documenting for future readers that this may not be what they're looking for (in that they may want a factory method that returns more than just Long and Double.)

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Zé Henriques · Accepted Answer · 2015-10-08 14:47:25Z

2

Better way is to use BigDecimal class.

BigDecimal n = new BigDecimal("1.0");

Methods for needed values

n.byteValue();  
n.intValue();  
n.shortValue();  
n.longValue();  
n.floatValue();  
n.doubleValue();

answered Oct 8, 2015 at 14:47

Zé Henriques

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Comments

OldCurmudgeon · Accepted Answer · 2015-10-08 14:12:46Z

1

You are probably looking for BigDecimal.

Please remember that a number can be represented in many forms as a string. e.g. 1 is the same number as 1.0000000.

answered Oct 8, 2015 at 14:12

OldCurmudgeon

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