Java BigDecimal 4 Basics: Warning, Casting, Simple Math & Comparison

1. Warning : Only Declaring BigDecimal with String

It is very easy to mistakenly declare like this

// Incorrect
new BigDecimal(100.11)

// This is correct
new BigDecimal("100.11")

It MUST BE STRING

You can check this quickly with jshell

2. Casting the Unknown Type to BigDecimal

Compare to the known type of Long , Float

new BigDecimal(longValue)
BigDecimal.valueOf(longValue)

Casting BigDecimalcan be problematic when type is unknown.

Example when this happen is when the nativeQuery=true from Spring JPA and want to cast it as BigDecimal.

Here is the solution.

// Object[] result
BigDecimal(result[1].toString())

3. How to do the Basic Math

The basic math will become harder to read

BigDecimal b1 = new BigDecimal("532.12");
BigDecimal b2 = new BigDecimal("123.21");

b1.add(b2)
b1.subtract(b2)
b1.multiply(b2)
b1.divide(b2, 2, RoundingMode.HALF_EVEN)

Chaining is possible

b1.add(b2).multiply(b2).subtract(b1).divide(b2, 4, RoundingMode.HALF_EVEN)

4. How to do the Comparison

The basic comparison will move to the right and always set the rightmost with 0 value

b1.compareTo(b2) < 0   // "<"
b1.compareTo(b2) > 0   // ">"    
b1.compareTo(b2) == 0  // "=="  
b1.compareTo(b2) != 0  // "!="  
b1.compareTo(b2) >= 0  // ">="    
b1.compareTo(b2) <= 0  // "<="   

If you try and see the comparison result, you will see something like this

Then it is why you will then compare it with 0