10 Java Stream Filter Examples

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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]

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