Sum in Lambda Expressions in Java 8

package nilpointer.net;

import java.util.ArrayList;
import java.util.List;

public class Demo {

	public static void main(String[] args) {

		List<Integer> numbers = new ArrayList<Integer>();
		numbers.add(5);
		numbers.add(2);
		numbers.add(11);
		numbers.add(-9);
		numbers.add(7);
		numbers.add(-4);

		int sum1 = numbers.stream().mapToInt(p -> p).sum();
		System.out.println("Sum 1: " + sum1);

		int sum2 = numbers.stream().filter(p -> p >= 3).mapToInt(p -> p).sum();
		System.out.println("Sum 2: " + sum2);

	}

}

Output

Sum 1: 12
Sum 2: 23