Chapter 19: BigDecimal

The BigDecimal class provides operations for arithmetic (add, subtract, multiply, divide), scale manipulation, rounding, comparison, hashing, and format conversion. The BigDecimal represents immutable, arbitrary-precision signed decimal numbers. This class shall be used in a necessity of high-precision calculation.

Section 19.1: Comparing BigDecimals

The method compareTo should be used to compare BigDecimals:

Commonly you should not use the equals method since it considers two BigDecimals equal only if they are equal in value and also scale:

Section 19.2: Using BigDecimal instead of float

Due to way that the float type is represented in computer memory, results of operations using this type can be inaccurate – some values are stored as approximations. Good examples of this are monetary calculations. If high precision is necessary, other types should be used. e.g. Java 7 provides BigDecimal.

import java.math.BigDecimal;

public class FloatTest {

public  static  void  main(String[]  args)  {

float accountBalance = 10000.00f;

System.out.println(“Operations  using  float:”);

System.out.println(“1000  operations  for  1.99”); for(int

 i  =  0;  i<1000;  i++){

accountBalance -= 1.99f;

}

System.out.println(String.format(“Account  balance  after  float  operations:  %f”, accountBalance));

BigDecimal accountBalanceTwo = new BigDecimal(“10000.00”);

System.out.println(“Operations  using  BigDecimal:”);

System.out.println(“1000  operations  for  1.99”);  BigDecimal

operation = new BigDecimal(“1.99”);

for(int  i  =  0;  i<1000;  i++){

accountBalanceTwo = accountBalanceTwo.subtract(operation);

}

System.out.println(String.format(“Account  balance  after  BigDecimal  operations:  %f”, accountBalanceTwo));

}

Output of this program is:

For a starting balance of 10000.00, after 1000 operations for 1.99, we expect the balance to be 8010.00. Using the float type gives us an answer around 8009.77, which is unacceptably imprecise in the case of monetary calculations. Using BigDecimal gives us the proper result.

Section 19.3: BigDecimal.valueOf()

The BigDecimal class contains an internal cache of frequently used numbers e.g. 0 to 10. The BigDecimal.valueOf() methods are provided in preference to constructors with similar type parameters i.e. in the below example a is preferred to b.

Section 19.4: Mathematical operations with BigDecimal

This example shows how to perform basic mathematical operations using BigDecimals.

BigDecimal a = new BigDecimal(“5”);

BigDecimal b = new BigDecimal(“7”); 

//Equivalent to result = a + b

BigDecimal  result  =  a.subtract(b);

System.out.println(result);

Result : 12

2.Subtraction

BigDecimal a = new BigDecimal(“5”);

BigDecimal b = new BigDecimal(“7”);

//Equivalent to result = a – b

BigDecimal  result  =  a.subtract(b);

System.out.println(result);

Result : -2

3.Multiplication

When multiplying two BigDecimals the result is going to have scale equal to the sum of the scales of operands.

Result : 36.89931

To change the scale of the result use the overloaded multiply method which allows passing MathContext – an object describing the rules for operators, in particular the precision and rounding mode of the result. For more information about available rounding modes please refer to the Oracle Documentation.

Result : 36.90

4.Division

Division is a bit more complicated than the other arithmetic operations, for instance consider the below example:

We would expect this to give something similar to : 0.7142857142857143, but we would get:

Result: java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result.

This would work perfectly well when the result would be a terminating decimal say if I wanted to divide 5 by 2, but for those numbers which upon dividing would give a non terminating result we would get an ArithmeticException. In the real world scenario, one cannot predict the values that would be encountered during the division, so we need to specify the Scale and the Rounding Mode for BigDecimal division. For more information on the Scale and Rounding Mode, refer the Oracle Documentation.

For example, I could do:

Result : 0.7142857143

5. Remainder or Modulus

BigDecimal b = new BigDecimal(“7”);

 //Equivalent to result = a % b

BigDecimal  result  =  a.remainder(b);

System.out.println(result);

Result : 5

6.Power

BigDecimal  a  =  new  BigDecimal(“5”); 

//Equivalent to result = a^10

BigDecimal  result  =  a.pow(10);

System.out.println(result);

Result : 9765625

7.Max

BigDecimal a = new BigDecimal(“5”);

BigDecimal b = new BigDecimal(“7”);

 //Equivalent to result = MAX(a,b)

BigDecimal  result  =  a.max(b);

System.out.println(result);

Result : 7

8.Min

BigDecimal a = new BigDecimal(“5”);

BigDecimal b = new BigDecimal(“7”); 

//Equivalent to result = MIN(a,b) BigDecimal  result  =  a.min(b);

System.out.println(result);

Result : 5

9. Move Point To Left

Result : 52.3449843776

10. Move Point To Right.

BigDecimal a  =  new  BigDecimal(“5234.49843776”);

 //Moves the decimal point to 3 places right of current position

BigDecimal  result  =  a.movePointRight(3); System.out.println(result);

Result : 5234498.43776

There are many more options and combination of parameters for the above mentioned examples (For instance, there are 6 variations of the divide method), this set is a non-exhaustive list and covers a few basic examples.

Section 19.5: Initialization of BigDecimals with value zero, one or ten

BigDecimal provides static properties for the numbers zero, one and ten. It’s good practise to use these instead of using the actual numbers:

• BigDecimal.ZERO
• BigDecimal.ONE
• BigDecimal.TEN

By using the static properties, you avoid an unnecessary instantiation, also you’ve got a literal in your code instead of a ‘magic number’.

Section 19.6: BigDecimal objects are immutable

If you want to calculate with BigDecimal you have to use the returned value because BigDecimal objects are immutable: