/**
 * The following program explains the mimicking of callback  function in java. 
 */
package java8pract;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * @author Prabhu KVN
 *
 */
public class CallBackFunction {

	ExecutorService executorservice = Executors.newFixedThreadPool(2);

	/**
	 * 
	 */
	public CallBackFunction() {
		// TODO Auto-generated constructor stub
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		CallBackFunction fun = new CallBackFunction();
		double val = 100;

		// handleResult is the call back function
		fun.findRoot(val, new ResultHandler() {

			@Override
			public void handleResult(double n) {
				// TODO Auto-generated method stub
				System.out.println("Root of " + val + " is " + n);
			}
		});
		System.out.println("Finding root in progress...");

	}

	public void findRoot(double number, ResultHandler handler) {

		RootFinder finder = new RootFinder(number, handler);

		executorservice.submit(finder);
		executorservice.shutdown();

	};

}

@FunctionalInterface
interface ResultHandler {
	public void handleResult(double n);
}

/**
 * A callable function which will execute a login and will call handler to
 * propagate the logic to an handler.
 * 
 * @author prabhu kvn
 *
 */
class RootFinder implements Callable<Double> {
	double number;
	ResultHandler handler;

	public RootFinder(double number, ResultHandler handler) {
		// TODO Auto-generated constructor stub
		this.number = number;
		this.handler = handler;
	}

	@Override
	public Double call() throws Exception {
		// TODO Auto-generated method stub
		double sqrt = Math.sqrt(number);
		handler.handleResult(sqrt);

		return sqrt;
	}
}