Addition for BigDecimal

I want to do some simple sums with some currency values expressed in BigDecimal type.

BigDecimal test = new BigDecimal(0);
System.out.println(test);
test.add(new BigDecimal(30));
System.out.println(test);
test.add(new BigDecimal(45));
System.out.println(test);

Obviously I do not understand well the BigDecimal arithmetics, see output behind.

Test
0
0
0

Can anyone help me out?

The BigDecimal is immutable so you need to do this:

BigDecimal result = test.add(new BigDecimal(30));
System.out.println(result);

It looks like from the Java docs here that add returns a new BigDecimal:

BigDecimal test = new BigDecimal(0);
System.out.println(test);
test = test.add(new BigDecimal(30));
System.out.println(test);
test = test.add(new BigDecimal(45));
System.out.println(test);

BigDecimal test = new BigDecimal(0);
System.out.println(test);
test = test.add(new BigDecimal(30));
System.out.println(test);
test = test.add(new BigDecimal(45));
System.out.println(test);

It's actually rather easy. Just do this:

BigDecimal test = new BigDecimal(0);
System.out.println(test);
test = test.add(new BigDecimal(30));
System.out.println(test);
test = test.add(new BigDecimal(45));
System.out.println(test);

See also: BigDecimal#add(java.math.BigDecimal)

BigInteger is immutable, you need to do this,

  BigInteger sum = test.add(new BigInteger(30));  
  System.out.println(sum);

//you can do in this way...as BigDecimal is immutable so cant set values except in constructor

BigDecimal test = BigDecimal.ZERO;
BigDecimal result = test.add(new BigDecimal(30));
System.out.println(result);

result would be 30

BigDecimal no = new BigDecimal(10); //you can add like this also
no = no.add(new BigDecimal(10));
System.out.println(no);

---

20

You can also do it like this:

BigDecimal A = new BigDecimal("10000000000");
BigDecimal B = new BigDecimal("20000000000");
BigDecimal C = new BigDecimal("30000000000");
BigDecimal resultSum = (A).add(B).add(C);
System.out.println("A+B+C= " + resultSum);

Prints:

> A+B+C= 60000000000

BigInteger is immutable, just like Strings. That means we cannot change it's content once the object is created, but we can re-assign it.

 BigInteger sum = test.add(new BigInteger(30));  
 System.out.println(sum);

.add() will return a new Object

Using Java8 lambdas

List<BigDecimal> items = Arrays.asList(a, b, c, .....);

items.stream().filter(Objects::nonNull).reduce(BigDecimal.ZERO, BigDecimal::add);

This covers cases where the some or all of the objects in the list is null.

BigDecimal demo = new BigDecimal(15);

It is immutable beacuse it internally store you input i.e (15) as final private final BigInteger intVal; and same concept use at the time of string creation every input finally store in private final char value[];.So there is no implmented bug.

Just another example to add BigDecimals. Key point is that they are immutable and they can be initialized only in the constructor. Here is the code:

import java.util.*;
import java.math.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc;
        boolean first_right_number = false;
        BigDecimal initBigDecimal = BigDecimal.ZERO;
        BigDecimal add1 = BigDecimal.ZERO;
        BigDecimal add2 = BigDecimal.ZERO;
        
        while (!first_right_number)
        {
            System.out.print("Enter a first single numeric value: ");
            sc = new Scanner(System.in);
            if (sc.hasNextBigDecimal()) 
            {
                first_right_number = true;
                add1 = sc.nextBigDecimal();
            }
        }
        
        boolean second_right_number = false;
        while (!second_right_number)
        {
            System.out.print("Enter a second single numeric value: ");
            sc = new Scanner(System.in);
            if (sc.hasNextBigDecimal()) 
            {
                second_right_number = true;
                add2 = sc.nextBigDecimal();
            }
        }
        BigDecimal result = initBigDecimal.add(add1).add(add2);
        System.out.println("Sum of the 2 numbers is: " + result.toString());
    }
}