data/train/RuthDirnfeld/1DV507/rd222dv_assign1/FunctionPointers.java

package rd222dv_assign1;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
import java.util.function.Predicate;

public class FunctionPointers {

	public static void main(String[] args) {
		System.out.println("Part 1: Apply predicates");
		List<Integer> list = Arrays.asList(45, 3, 24, 16, 1, 1, 3, 8, 7, 6, 10, 12, 17, 22, 30);

		System.out.print("Print all numbers: ");
		Predicate<Integer> all = n -> true;
		selectAndPrint(list, all); //

		System.out.print("\nPrint all odd numbers: ");
		Predicate<Integer> odd = n -> n % 2 != 0; // Must be updated
		selectAndPrint(list, odd);

		System.out.print("\nPrint all numbers greater than 10: ");
		Predicate<Integer> aboveTen = n -> n > 10; // Must be updated
		selectAndPrint(list, aboveTen);

		System.out.println("\n\nPart 2: Apply functions");
		List<Double> numbers = Arrays.asList(1.0, 16.0, 25.0, 81.0);
		System.out.println("Original: " + numbers);
		System.out.println("Square root: " + applyFunction(numbers, Math::sqrt));
		System.out.println("Power of two: " + applyFunction(numbers, FunctionPointers::powerOfTwo));
	}

	// Prints all elements in the list where predicate evaluates to true
	public static void selectAndPrint(List<Integer> list, Predicate<Integer> predicate) {

		 for(Integer n: list) {
				
	         if(predicate.test(n)) {
	            System.out.print(n + " ");
	         }
		 }
	}

	// Returns a new list containing the numbers resulting from applying fx
	// on the input list numbers
	private static List<Double> applyFunction(List<Double> numbers, Function<Double, Double> fx) {

		List<Double> appliedNumbers = new ArrayList<>();
	     for (Double n : numbers) {
	        appliedNumbers.add(Double.valueOf(fx.apply(n)));
	     }
		return appliedNumbers;
	}

	private static Double powerOfTwo(Double d) {
		return d*d; // Must be updated
	}
}