Riemann Integral

Partition.java

public class Partition {
	private double a;
	private double b;
	private double N;
	
	public Partition(double a, double b, double N) {
		super();
		this.a = a;
		this.b = b;
		this.N = N;
	}

	public double x(int n) {
		double len = b - a;
		double z = len / N;
		return a + n * z;
	}
	
	public double integrate(Function f) {
		double sum = 0;
		for (int i = 1; i < N; i++) {
			sum += f.f(x(i)) * (x(i) - x(i-1));
		}
		return sum;
	}
	
	@FunctionalInterface
	interface Function {
		public double f(double x);
	}
	
	public static void main(String[] args) {
		double d = new Partition(0, Math.PI, 100000).integrate(x -> Math.sin(x));
		System.out.println(d);
	}
 }