How to Use if/else Logic in Java 8 Streams

Table of Contents

1. Overview
2. Conventional if/else Logic Within forEach()
3. if/else Logic With filter()
4. Conclusion

1. Overview

In this tutorial, we’re going to demonstrate how to implement if/else logic with Java 8 Streams. As part of the tutorial, we’ll create a simple algorithm to identify odd and even numbers.

We can take a look at this article to catch up on the Java 8 Stream basics.

2. Conventional if/else Logic Within forEach()

First of all, let’s create an Integer List and then use conventional if/else logic within the Integer stream forEach() method:

List<Integer> ints = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

ints.stream()
    .forEach(i -> {
        if (i.intValue() % 2 == 0) {
            Assert.assertTrue(i.intValue() % 2 == 0);
        } else {
            Assert.assertTrue(i.intValue() % 2 != 0);
        }
    });

Our forEach method contains if-else logic which verifies whether the Integer is an odd or even number using the Java modulus operator.

3. if/else Logic With filter()

Secondly, let’s look at a more elegant implementation using the Stream filter() method:

Stream<Integer> evenIntegers = ints.stream()
    .filter(i -> i.intValue() % 2 == 0);
Stream<Integer> oddIntegers = ints.stream()
    .filter(i -> i.intValue() % 2 != 0);

evenIntegers.forEach(i -> Assert.assertTrue(i.intValue() % 2 == 0));
oddIntegers.forEach(i -> Assert.assertTrue(i.intValue() % 2 != 0));

Above we implemented the if/else logic using the Stream filter() method to separate the Integer List into two Streams, one for even integers and another for odd integers.