Java 8 Lambda Example

FunctionalJava.java

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.function.ToIntFunction;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

import static java.lang.System.out;

public class FunctionalJava {

    private List<Integer> list = new ArrayList<>();

    public FunctionalJava() {
        createList();
    }

    public static void main(String[] args) {
        FunctionalJava fj = new FunctionalJava();

        fj.doTimedCall(FunctionalJava::viaFor);
        fj.doTimedCall(FunctionalJava::viaSum);
        fj.doTimedCall(FunctionalJava::viaReduce);

        // Inlined lambda. This is simply duplicating the functionality of viaSum()
        fj.doTimedCall(func -> fj.list
                .stream()
                .mapToInt(Integer::intValue)
                .filter(value -> value > 0)
                .sum());
    }

    public void doTimedCall(ToIntFunction<FunctionalJava> func) {
        long startTime = System.currentTimeMillis();
        // Here is where the magic happens.
        int sum = func.applyAsInt(this);
        long endTime = System.currentTimeMillis();
        out.println(sum + ". Took " + (endTime - startTime) + "ms");
    }

    public int viaFor() {
        int sum = 0;
        for (int i : list) {
            sum += i;
        }
        return sum;
    }

    public int viaSum() {
        return list.stream()
                .mapToInt(Integer::intValue)
                .sum();
    }

    public int viaReduce() {
        return list.stream()
                .mapToInt(Integer::intValue)
                .reduce(0, (a, b) -> a + b);
    }

    private void createList() {
        Random random = new Random();
        IntStream intStream = random.ints(-100, 100);
        list = intStream
                .limit(10000)
                .boxed()
                .collect(Collectors.toList());
    }
}