How to get integer and fraction portions of a BigDecimal in Java

Question

For a BigDecimal number such as 42.7, how can I tear this apart to get the integer part (42) and the decimal fractional part (0.7)?

I would like to retrieve both as BigDecimal objects. But I will take what I can get and make BigDecimal object from them.

Answer 1

tl;dr

myBigDecimal
.divideAndRemainder( BigDecimal.ONE )
[ 0 ]                                    // for integer part

…and…

[ 1 ]                                    // for fraction part

BigDecimal::divideAndRemainder

The BigDecimal class offers some methods for this.

The BigDecimal::divideAndRemainder method divides your original number by another number. The result is an array of two BigDecimal objects, the first being the integer portion and the second being the fraction amount.

To achieve your goal, we merely need to divide by one. The BigDecimal class offers a constant object for the value of one: BigDecimal.ONE.

BigDecimal input = new BigDecimal( "42.7" ) ;
BigDecimal[] parts = input.divideAndRemainder( BigDecimal.ONE );

Dump to console.

System.out.println( Arrays.toString( parts ) );

[42.0, 0.7]

Grab each piece from the array.

BigDecimal input = new BigDecimal( "42.7" ) ;
BigDecimal[] parts = input.divideAndRemainder( BigDecimal.ONE );
BigDecimal integerPart = parts[ 0 ] ;
BigDecimal fractionPart = parts[ 1 ] ;

If you only need one part:

• myBigDecimal.divideAndRemainder( BigDecimal.ONE )[ 0 ] integer part
• myBigDecimal.divideAndRemainder( BigDecimal.ONE )[ 1 ] fraction part

Addition puts them together again.

BigDecimal humptyDumpty = integerPart.add( fractionPart ) ;

Answer 2

setScale()

I think I’d go for setScale().

    BigDecimal bd = new BigDecimal("42.7");
    
    BigDecimal integerPart = bd.setScale(0, RoundingMode.DOWN);
    BigDecimal fractionalPart = bd.subtract(integerPart);
    
    System.out.println(integerPart);
    System.out.println(fractionalPart);

42
0.7

It seems to me to be clear to read.