[Java8] Stream reduce sample

ReduceTest.java

import java.util.Arrays;
import java.util.Optional;

public class ReduceTest {

	public static void main(String[] args) {
		Optional<Sum> summary = Arrays.asList(new Sum(1, 10),new Sum(2, 15),new Sum(3, 5)).stream().reduce((sum1,sum2) -> {
			if (Optional.ofNullable(sum1).isPresent() == false) {
				System.out.println("Sum1 is empty.");
				return sum2;
			}
			if (Optional.ofNullable(sum2).isPresent() == false) {
				System.out.println("Sum2 is empty.");
				return sum1;
			}
			
			return new Sum(sum1.getA() + sum2.getA(), sum1.getB() + sum2.getB());
		});
		
		System.out.println("[RESULT] a = " + summary.get().getA() + " , b = " + summary.get().getB());

	}
	
	static class Sum {
		
		private final long a;
		private final long b;
		
		public Sum(long a, long b) {
			super();
			this.a = a;
			this.b = b;
		}
		public long getA() {
			return a;
		}
		public long getB() {
			return b;
		}
	}

}