Dynamically formatting a string in java

Question

Is there a way to dynamically format a float value?

I thought i could do something like this:

System.out.println(new BigDecimal(String.format("%" + k + "s", answer)).toPlainString());

Where k is the increments each time through a loop... however, this doesn't seem to do the trick...

i want the numbers to appear like this:

any ideas?

is k supposed to be the precision? What kind of format are you tryign to do? Also, why are you creating a BigDecimal based on a String? I'm really confused about what you are trying to do here. — crush
– crush, Commented Sep 11, 2013 at 20:55
Hehe. Do you need the actual float value, or just string printing? You could hack it and use substring. — Georgian
– Georgian, Commented Sep 11, 2013 at 20:59
let's say k is 4 and you're input is 0.789, should it print out "0.7890"? — Hans Z
– Hans Z, Commented Sep 11, 2013 at 20:59
also, I noticed that you don't seem to round... is this what you want? — Hans Z
– Hans Z, Commented Sep 11, 2013 at 21:00

Seth Hoenig · Accepted Answer · 2013-09-11 21:02:38Z

7

for (int i=3; i<10; i++) {
    System.out.println(String.format("%1." + i + "f", Math.PI));
}

Something like that should work

[tmp] % java Foo
3.142
3.1416
3.14159
3.141593
3.1415927
3.14159265
3.141592654

answered Sep 11, 2013 at 21:02

Seth Hoenig

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2 Comments

Hans Z Over a year ago

this would work but the example in the question doesn't round.

Georgian Over a year ago

Wanted to mention "%."+i+"f" but I thought I was thinking in C++. Very good answer.

Java Devil · Accepted Answer · 2013-09-11 22:19:00Z

2

Using a NumberFormat can be done like this example

 float f = 0.342566246
 NumberFormat n = NumberFormat.getInstance()
 for(int i = 2; i< 6;i++)
 {
     n.setMaximumFractionDigits(i)
     System.out.println(n.format(f))
 }

Gives, which rounds.

You can control rounding by adding a RoundingMode eg adding

n.setRoundingMode(RoundingMode.DOWN);

Gives

edited Sep 11, 2013 at 22:19

answered Sep 11, 2013 at 21:03

Java Devil

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Comments

willeM_ Van Onsem · Accepted Answer · 2013-09-11 20:55:07Z

0

Have a look at: http://docs.oracle.com/javase/tutorial/java/data/numberformat.html

I can't help you any further since I don't know the format you're interested in.

answered Sep 11, 2013 at 20:55

willeM_ Van Onsem

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1 Comment

Hans Z Over a year ago

Hey, @CommuSoft, you should try to summarize the contents of your link instead of having just a link in answers in case of linkrot. meta.stackexchange.com/questions/8231/…

Georgian · Accepted Answer · 2013-09-11 21:08:02Z

0

If you don't need the actual float value of your variables, you can just print them out in the loop using the subString API from String.

The advantage is that your formatted variable won't be rounded. This is a hack-ish alternative to the other two answers.

edited Sep 11, 2013 at 21:08

answered Sep 11, 2013 at 21:02

Georgian

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