Double Precision Calculation in Java

DoubleMath

import java.math.BigDecimal;

import static DoubleMath.Operation.ADD;
import static DoubleMath.Operation.DIVIDE;
import static DoubleMath.Operation.MULTIPLY;
import static DoubleMath.Operation.SUBSTRACT;
import static java.math.RoundingMode.HALF_EVEN;

public class DoubleMath {
	private double leftOperand;
	private Operation operation;

	private DoubleMath(Operation operation, double leftOperand) {
		this.operation = operation;
		this.leftOperand = leftOperand;
	}

	public static DoubleMath divide(double divisor) {
		return new DoubleMath(DIVIDE, divisor);
	}

	public static DoubleMath add(double divisor) {
		return new DoubleMath(ADD, divisor);
	}

	public static DoubleMath substract(double divisor) {
		return new DoubleMath(SUBSTRACT, divisor);
	}

	public static DoubleMath multiply(double divisor) {
		return new DoubleMath(MULTIPLY, divisor);
	}

	public double by(double rightOperand) {
		BigDecimal leftDecimal = new BigDecimal(leftOperand);
		BigDecimal rightDecimal = new BigDecimal(rightOperand);
		switch (operation) {
			case ADD:
				return leftDecimal.add(rightDecimal).setScale(2, HALF_EVEN).doubleValue();
			case SUBSTRACT:
				return leftDecimal.subtract(rightDecimal).setScale(2, HALF_EVEN).doubleValue();
			case MULTIPLY:
				return leftDecimal.multiply(rightDecimal).setScale(2, HALF_EVEN).doubleValue();
			case DIVIDE:
				return leftDecimal.divide(rightDecimal, 2, HALF_EVEN).doubleValue();
		}
		throw new RuntimeException("no op : " + operation);
	}

	public double to(double rightOperand) {
		return by(rightOperand);
	}

	enum Operation {
		ADD, MULTIPLY, DIVIDE, SUBSTRACT;
	}

}

DoubleMathTest

import org.junit.Test;

import static DoubleMath.*;
import static org.fest.assertions.Assertions.assertThat;

public class DoubleMathTest {

	@Test
	public void should_add_with_two_digits() throws Exception {
		assertThat(add(5.6).to(5.8)).isEqualTo(11.4);
	}

	@Test
	public void should_substract_with_two_digits() throws Exception {
		assertThat(substract(1.35).to(1.3)).isEqualTo(0.05);
	}

	@Test
	public void should_multiply_with_two_digits() throws Exception {
		assertThat(multiply(12).by(25.4)).isEqualTo(304.8);
	}

	@Test
	public void should_divide_with_two_digits() throws Exception {
		assertThat(divide(527).by(480)).isEqualTo(1.1);
	}

}