10 Java Stream Filter Examples

In this blog post, we will demonstrate different ways to use the filter() method in Java streams to perform filtering operations based on various conditions.

1. Filtering even numbers:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
List<Integer> evenNumbers = numbers.stream()
                                  .filter(n -> n % 2 == 0)
                                  .collect(Collectors.toList());
System.out.println(evenNumbers); // Output: [2, 4, 6, 8, 10]

2. Filtering strings of a specific length:

List<String> words = Arrays.asList("apple", "banana", "car", "dog", "elephant");
List<String> lengthThreeWords = words.stream()
                                     .filter(s -> s.length() == 3)
                                     .collect(Collectors.toList());
System.out.println(lengthThreeWords); // Output: [car, dog]

3. Filtering strings that start with a specific letter:

List<String> words = Arrays.asList("apple", "banana", "car", "dog", "elephant");
List<String> startsWithB = words.stream()
                               .filter(s -> s.startsWith("b"))
                               .collect(Collectors.toList());
System.out.println(startsWithB); // Output: [banana]

4. Filtering objects based on a condition:

List<Person> people = Arrays.asList(
    new Person("John", 25),
    new Person("Alice", 30),
    new Person("Bob", 20),
    new Person("Jane", 35)
);
List<Person> adults = people.stream()
                            .filter(p -> p.getAge() >= 18)
                            .collect(Collectors.toList());
System.out.println(adults); // Output: [John, Alice, Bob, Jane]

5. Filtering distinct elements:

List<Integer> numbers = Arrays.asList(1, 2, 3, 2, 4, 5, 3, 1);
List<Integer> distinctNumbers = numbers.stream()
                                       .distinct()
                                       .collect(Collectors.toList());
System.out.println(distinctNumbers); // Output: [1, 2, 3, 4, 5]

6. Filtering using multiple conditions:

List<Person> people = Arrays.asList(
    new Person("John", 25),
    new Person("Alice", 30),
    new Person("Bob", 20),
    new Person("Jane", 35)
);
List<Person> filteredPeople = people.stream()
                                   .filter(p -> p.getAge() >= 18 && p.getAge() <= 30)
                                   .collect(Collectors.toList());
System.out.println(filteredPeople); // Output: [John, Alice, Bob]

7. Filtering using a predicate:

List<String> words = Arrays.asList("apple", "banana", "car", "dog", "elephant");
Predicate<String> predicate = s -> s.length() > 3 && s.contains("a");
List<String> filteredWords = words.stream()
                                  .filter(predicate)
                                  .collect(Collectors.toList());
System.out.println(filteredWords); // Output: [apple, banana, elephant]

8. Filtering using a custom method:

List<String> words = Arrays.asList("apple", "banana", "car", "dog", "elephant");
List<String> filteredWords = words.stream()
                                  .filter(this::startsWithVowel)
                                  .collect(Collectors.toList());

private boolean startsWithVowel(String word) {
    return word.matches("[aeiouAEIOU].*");
}

System.out.println(filteredWords); // Output: [apple, elephant]

9. Filtering using negation:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
List<Integer> filteredNumbers = numbers.stream()
                                       .filter(n -> n % 2 != 0)
                                       .collect(Collectors.toList());
System.out.println(filteredNumbers); // Output: [1, 3, 5]

10. Filtering using a range of values:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
List<Integer> filteredNumbers = numbers.stream()
                                       .filter(n -> n > 5 && n < 9)
                                       .collect(Collectors.toList());
System.out.println(filteredNumbers); // Output: [6, 7, 8]