Calculator Example

Let's build a calculator! Using the built-in BigInteger class we can easily construct a fluent api to access some of the math operations.

Descriptor descriptor = Flapi.builder()
	.setDescriptorName("Calculator")
	.setPackage("unquietcode.tools.flapi.examples.calculator.builder")
	.setStartingMethodName("begin")

	.startBlock("Calculation", "$(int startingValue)").last()
		.addMethod("plus(int value)").any()
		.addMethod("minus(int value)").any()
		.addMethod("times(int value)").any()
		.addMethod("divide(int value)").any()
		.addMethod("power(int value)").any()
		.addMethod("mod(int value)").any()
		.addMethod("abs()").any()

		.addMethod("equals()").last(ObjectWrapper.class)
	.endBlock()
.build();

The return type is set to ObjectWrapper because we need an immutable reference to hold on to, but the BigInteger class is itself immutable (math operations return a new object).

The usage is fairly straightforward, and looks something like this:

	ObjectWrapper _result = CalculatorGenerator.begin(new CalculatorHelperImpl())
		.$(0)
		.plus(1)
		.plus(1)
		.power(5)
		.divide(2)
	.equals();

	BigInteger result = (BigInteger) _result.get();
	System.out.println(result);

If you were to include this builder in a project, you might want to wrap some of the messiness involved with instantiating a new builder. A user of the calculator should not have to instantiate the helper or remember the $(...) method to begin. Here I've introduced a Calculator class which wraps all this up.

	static class Calculator {
		static CalculationBuilder<ObjectWrapper<BigInteger>> begin(int startingValue) {
			CalculatorBuilder result = CalculatorGenerator.begin(new CalculatorHelperImpl());

			@SuppressWarnings("unchecked")
			CalculationBuilder<ObjectWrapper<BigInteger>> started
				= (CalculationBuilder<ObjectWrapper<BigInteger>>) result.$(startingValue);

			return started;
		}
	}

And now the usage is just a tiny bit cleaner:

	ObjectWrapper<BigInteger> result = Calculator
	.begin(0)
		.plus(1)
		.plus(1)
		.power(5)
		.divide(2)
	.equals();

	System.out.println(result.get());

The full example can be found here.