Formatting Integer with a decimal point

Question

I have an integer value that is read from a PLC device via bluetooth and the first digit represent one decimal place. For example: 100 must be formatted to 10.0. Another examples:

500 -> 50.0
491 -> 49.1
455 -> 45.5

The following line will make it okay:

data11.put("Text2", String.format("%.1f", (float)(mArray[18] & 0xFF | mArray[19] << 8) / 10.0));

But... Is there another way to do the same using String.format without divide by 10.0?

Thank you

Without dividing? I don't believe so, no. Check [this SO answer](https://stackoverflow.com/questions/12990451/print-integer-with-2-decimal-places-in-java). — AntonH, Mar 15 '17 at 03:25
Can you give more details of the contents of `myArray`, what you'd want to do might be possible with byte operations perhaps — buræquete, Mar 15 '17 at 03:31
You are calculating one tenth of something, so you could multiply by `0.1` instead? — Elliott Frisch, Mar 15 '17 at 03:31
Thank you for the answers. I'm newbie to Java and I was wondering maybe String.format could produce the same result without using any extra operation. — Madbyte, Mar 15 '17 at 16:48
I think this question is a duplicate, but I have not yet found the last time it was asked. — Ole V.V., Mar 15 '17 at 18:21

score 3 · Answer 1 · answered Mar 15 '17 at 03:35

3

How about the following way?

x = x.substring(0, x.length() - 1) + "." + x.substring(x.length() - 1);

answered Mar 15 '17 at 03:35

VHS

9,534
3
19
43

I like it. It won’t give what I think you would want if the number was 0, but this special case can be handled with `if`-`else` if needed. – Ole V.V. Mar 15 '17 at 18:15

YoYo · Answer 2 · 2017-03-15T20:18:01.200

If your concern is the internal rounding that happens with a float representation, consider using BigDecimal. Like:

BigDecimal v = BigDecimal.valueOf(500,1);
System.out.println(v.toString());

or combined as

System.out.println(BigDecimal.valueOf(500,1).toString());

or maybe you need to use

System.out.println(BigDecimal.valueOf(500,1).toPlainString());

And to answer your original question directly, even this works:

BigDecimal v11 = BigDecimal.valueOf(mArray[18] & 0xFF | mArray[19] << 8,1);
data11.put("Text2", String.format("%.1f", v11));

But the real question is if this is all really needed or not.

score 1 · Answer 3 · answered Mar 15 '17 at 03:38

How about this?

System.out.println(500*0.1);
System.out.println(491*0.1);
System.out.println(455*0.1);

Output

50.0                                                                                                                                                                                                  
49.1                                                                                                                                                                                                  
45.5

score 0 · Answer 4 · answered Mar 15 '17 at 05:58

I would go by integer division and modulo:

private static String format(int value) {
    return (value / 10) + "." + Math.abs(value % 10);
}

Math.abs() can be removed if not using negative numbers:

private static String format(int value) {
    return (value / 10) + "." + (value % 10);
}

Obviously the method can be inlined...

Formatting Integer with a decimal point

4 Answers4

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