Introduction of JCalc (www.jdice.org) open source library for easier writing formula and calculations in Java. Presented at JavaCro'14, 2014/05/12.

1. Calculations in Java with open source API
Author: Davor Sauer
www.jdice.org

2. Content
 Calculations in Java- basics
 Calculations in Java with JCalc
 Comparison of complex calculation with plain Java and JCalc
 Features
 Questions

4. Calculations in Java- basics
Example: Simple calculation: If you pay $2.00 for a beer that costs $1.10,
how much changes do you get?
System.out.println(2.00 - 1.10); Answers:
a) .9
b) .90
c) 0.899999999999
d) None of the above
BigDecimal payment = new BigDecimal(2.00);
BigDecimal cost = new BigDecimal(1.10);
System.out.println(payment.subtract(cost));
Answers:
a) .9
b) .90
c) 0.899999999999
d) None of the above
=> 0.89999999991118215802998747...
BigDecimal payment = new BigDecimal("2.00");
BigDecimal cost = new BigDecimal("1.10");
System.out.println(payment.subtract(cost));
Answers:
a) .9
b) 0.90
c) 0.899999999999
d) None of the above

5. Java + JCalc
...more sugar?

6. Calculations in Java- basics
Example: Simple calculation: If you pay $2.00 for a beer that costs $1.10,
how much changes do you get?
System.out.println(Calculator.builder().val(2.00).sub(1.10).calculate());
Answers:
a) 0.9
b) .90
c) 0.899999999999
d) None of the aboveNum p = new Num(2.00);
Num c = new Num(1.10);
System.out.println(Calculator.builder().val(p).sub(c).calculate()); Answers:
a) .9
b) .90
c) 0.899999999999
d) None of the above
Num p = new Num("2.00");
Num c = new Num("1.10");
System.out.println(Calculator.builder().val(p).sub(c).setStripTrailingZeros(false).calculate());
System.out.println(Calculator.builder("2.00 - 1.10").setStripTrailingZeros(false).calculate());
Answers:
a) .9
b) 0.90
c) 0.899999999999
d) None of the above
0.9
0.899999999999
0.89999999991118215802998747...

7. Complex example
 Calculate fixed monthly payment for a fixed rate mortgage by Java
BigDecimal interestRate = new BigDecimal("6.5"); // fixed yearly interest rate in %
BigDecimal P = new BigDecimal(200000);
BigDecimal paymentYears = new BigDecimal(30);
// monthly interest rate => 6.5 / 12 / 100 = 0.0054166667
BigDecimal r = interestRate.divide(new BigDecimal(12), 10, BigDecimal.ROUND_HALF_UP).divide(new BigDecimal(100), 10, BigDecimal.ROUND_HALF_UP);
// numerator
// => 0.005416666 * 200000 = 1083.3333400000
BigDecimal numerator = r.multiply(P);
// denominator
r = r.add(new BigDecimal(1)); // => 1.0054166667
BigDecimal pow = new BigDecimal(30 * 12); // N = 30 * 12
// => 1.0054166667 ^ (-30 * 12) ===> 1 / 1.005416666 ^ (30 * 12)
BigDecimal one = BigDecimal.ONE;
BigDecimal r_pow = r.pow(pow.intValue()); // => 1.0054166667 ^ 360 = 6.99179805731691416804....
r_pow = one.divide(r_pow, 10, BigDecimal.ROUND_HALF_UP); // => 1 / 6.991798.. = 0.1430247258
// => 1 - 0.1430247258 = 0.8569752742
BigDecimal denominator = new BigDecimal(1);
denominator = denominator.subtract(r_pow);
// => 1083.3333400000 / 0.8569752742 = 1264.1360522464
BigDecimal c = numerator.divide(denominator, 10, BigDecimal.ROUND_HALF_UP);
c = c.setScale(2, BigDecimal.ROUND_HALF_UP);
System.out.println("c = " + c);
 Line of code: 15

8. Complex example
 Calculate fixed monthly payment for a fixed rate mortgage by Java
Num interestRate = new Num(6.5); // fixed yearly interest rate in %
Num P = new Num(200000);
Num paymentYears = new Num(30);
// monthly interest rate : r = 6.5 / 100 / 12
Num r = Calculator.builder().openBracket().val(interestRate).div(100).closeBracket().div(12).calculate();
// N = 30 * 12 * -1
Num N = Calculator.builder().val(paymentYears).mul(12).mul(-1).calculate();
// c = (r * P) / (1 / (1 + r)^N
Calculator c = new Calculator()
.openBracket()
.val(r).mul(P)
.closeBracket() // numerator
.div() // ---------------
.openBracket() // denumerator
.val(1).sub().openBracket().val(1).add(r).closeBracket().pow(N)
.closeBracket();
Num result = c.calculate().setScale(2);
System.out.println("c = " + result);  Line of code: 8

9. Complex example
 Calculate fixed monthly payment for a fixed rate mortgage by Java
Num interestRate = new Num("A", 6.5);
Num P = new Num("B", 200000);
Num paymentYears = new Num("C", -30);
Calculator c = Calculator.builder("((A / 100 / 12) * B) / (1 - ((1 + (A / 100 / 12)) ^ (C * 12)))", interestRate, P, paymentYears);
Num result = c.calculate();
System.out.println("c = " + result.setScale(2));
 Line of code: 6

10. Feature: Show calculation steps
Num interestRate = new Num("A", 6.5);
Num P = new Num("B", 200000);
Num paymentYears = new Num("C", -30);
Calculator c = Calculator.builder("((A / 100 / 12) * B) / (1 - ((1 + (A / 100 / 12)) ^ (C * 12)))", interestRate, P, paymentYears);
c.setScale(10);
c.setTracingSteps(true); // track calculation steps
Num result = c.calculate();
for(Step step : c.getTracedSteps())
System.out.println(step);
System.out.println("c = " + result.setScale(2));
Output:
6.5 / 100 = 0.065
0.065/ 12 = 0.0054166667
0.0054166667 * 200000 = 1083.33334
6.5 / 100 = 0.065
0.065/ 12 = 0.0054166667
1 + 0.0054166667 = 1.0054166667
-30 * 12 = -360
1.0054166667 ^ -360 = 0.1430247258
1 - 0.1430247258 = 0.8569752742
1083.33334/ 0.8569752742 = 1264.1360522464
c = 1264.14

11. Feature: Modularity
Calculator calc = new Calculator();
calc.use(QuestionOperator.class); // use custom operator '?'
calc.use(SumFunction.class); // use custom function 'sum'
calc.expression("2 ? 2 + 5 - 1 + sum(1,2,3,4)");
@SingletonExtension
public class QuestionOperator implements Operator {
....
// implementation for ‘?’ operator
....
}
@SingletonExtension
public class SumFunction implements Function {
....
// implementation for ‘sum’ function
....
}

12. Feature: Default configuration
roundingMode=HALF_UP
scale=2
stripTrailingZeros=true
decimalSeparator.out='.'
decimalSeparator.in='.'
numconverter[0]=org.jdice.calc.test.NumTest$CustomObject > org.jdice.calc.test.NumTest$CustomObjectNumConverter
operator[0]=org.jdice.calc.test.CustomOperatorFunctionTest$QuestionOperator
function[0]=org.jdice.calc.test.CustomOperatorFunctionTest$SumFunction
Configure default properties with 'jcalc.properties' file in class path

13. Questions, ideas, suggestions…
Project page: www.jdice.org