CODEWITHSUNDEEP
javajpascaleprecisionbigdecimal
jpadilladev
jpadilladev

Reputation: 1946

BigDecimal, precision and scale

I'm using BigDecimal for my numbers in my application, for example, with JPA. I did a bit of researching about the terms 'precision' and 'scale' but I don't understand what are they exactly.

Can anyone explain me the meaning of 'precision' and 'scale' for a BigDecimal value?

@Column(precision = 11, scale = 2)

Thanks!

Upvotes: 122

Views: 174878

Answers (6)

imAmanRana
imAmanRana

Reputation: 123

The JPA annotation @Column(precision = 11, scale = 2) for BigDecimal variable translates to DECIMAL(11,2) in the MYSQL database.

This means, the column can store a value having 11 digits in total, with 2 digits allowed after the decimal. ie. the Range here would be [-999999999.99,999999999.99]

Upvotes: 0

Austin
Austin

Reputation: 8585

A BigDecimal is defined by two values: an arbitrary precision integer and a 32-bit integer scale. The value of the BigDecimal is defined to be unscaledValue*10^{-scale}.

Precision:

The precision is the number of digits in the unscaled value. For instance, for the number 123.45, the precision returned is 5.

So, precision indicates the length of the arbitrary precision integer. Here are a few examples of numbers with the same scale, but different precision:

  • 12345 / 100000 = 0.12345 // scale = 5, precision = 5
  • 12340 / 100000 = 0.1234 // scale = 4, precision = 4
  • 1 / 100000 = 0.00001 // scale = 5, precision = 1

In the special case that the number is equal to zero (i.e. 0.000), the precision is always 1.

Scale:

If zero or positive, the scale is the number of digits to the right of the decimal point. If negative, the unscaled value of the number is multiplied by ten to the power of the negation of the scale. For example, a scale of -3 means the unscaled value is multiplied by 1000.

This means that the integer value of the ‘BigDecimal’ is multiplied by 10^{-scale}.

Here are a few examples of the same precision, with different scales:

  • 12345 with scale 5 = 0.12345
  • 12345 with scale 4 = 1.2345
  • …
  • 12345 with scale 0 = 12345
  • 12345 with scale -1 = 123450 †

BigDecimal.toString:

The toString method for a BigDecimal behaves differently based on the scale and precision. (Thanks to @RudyVelthuis for pointing this out.)

  • If scale == 0, the integer is just printed out, as-is.
  • If scale < 0, E-Notation is always used (e.g. 5 scale -1 produces "5E+1")
  • If scale >= 0 and precision - scale -1 >= -6 a plain decimal number is produced (e.g. 10000000 scale 1 produces "1000000.0")
  • Otherwise, E-notation is used, e.g. 10 scale 8 produces "1.0E-7" since precision - scale -1 equals unscaledValue*10^{-scale} is less than -6.

More examples:

  • 19/100 = 0.19 // integer=19, scale=2, precision=2
  • 1/1000 = 0.0001 // integer=1, scale = 4, precision = 1

Upvotes: 178

Shadyar
Shadyar

Reputation: 845

Precision is the total number of significant digits in a number. Scale is the number of digits to the right of the decimal point.

Examples:

123.456 Precision=6 Scale=3

10 Precision=2 Scale=0

-96.9923 Precision=6 Scale=4

0.0 Precision=1 Scale=1

Negative Scale

For a negative scale value, we apply the following formula: result = (given number) * 10 ^ (-(scale value)) Example

Given number = 1234.56

scale = -5

-> (1234.56) * 10^(-(-5))

-> (1234.56) * 10^(+5)

-> 123456000

Reference: https://www.logicbig.com/quick-info/programming/precision-and-scale.html

Upvotes: 7

hamena314
hamena314

Reputation: 3109

  • Precision: Total number of significant digits

  • Scale: Number of digits to the right of the decimal point

See BigDecimal class documentation for details.

Upvotes: 95

adranale
adranale

Reputation: 2874

From your example annotation the maximum digits is 2 after the decimal point and 9 before (totally 11): 123456789,01

Upvotes: 3

Andy Turner
Andy Turner

Reputation: 140554

Quoting Javadoc:

The precision is the number of digits in the unscaled value.

and

If zero or positive, the scale is the number of digits to the right of the decimal point. If negative, the unscaled value of the number is multiplied by ten to the power of the negation of the scale. For example, a scale of -3 means the unscaled value is multiplied by 1000.

Upvotes: 4

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