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

4. Conclusion

In this quick article, we’ve explored how to create a Java 8 Stream and how to implement if/else logic using the forEach() method.

Furthermore, we learned how to use the Stream filter method to achieve a similar result, in a more elegant manner.

Finally, the complete source code used in this tutorial is available over on Github.

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