Java Stream filter() Example

1. Introduction

This tutorial explains how to use the filter() method in the Java Stream API. The filter() method is an intermediate operation that tests each element of a stream to see if it matches a given predicate. If the element satisfies the predicate, it is included in the resulting stream.

Key Points

1. filter() evaluates each element in a stream using a specified predicate.

2. Only elements that pass the predicate test are included in the resulting stream.

3. It is used extensively for conditional checks within streams, such as filtering collections based on conditions.

2. Program Steps

1. Create a Stream of elements.

2. Apply the filter() method to exclude certain elements based on a condition.

3. Collect or process the results to demonstrate the effects of filtering.

3. Code Program

import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class StreamFilterExample {

    public static void main(String[] args) {
        // Stream of integers
        Stream<Integer> numberStream = Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        // Filter out even numbers
        List<Integer> evenNumbers = numberStream.filter(n -> n % 2 == 0).collect(Collectors.toList());
        System.out.println("Even numbers: " + evenNumbers);

        // Stream of strings
        Stream<String> stringStream = Stream.of("apple", "banana", "cherry", "date", "elderberry");

        // Filter strings longer than 5 characters
        List<String> longFruits = stringStream.filter(s -> s.length() > 5).collect(Collectors.toList());
        System.out.println("Fruits longer than 5 characters: " + longFruits);
    }
}

Output:

Even numbers: [2, 4, 6, 8, 10]
Fruits longer than 5 characters: [banana, cherry, elderberry]

Explanation:

1. Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) creates a stream of integers.

2. numberStream.filter(n -> n % 2 == 0) applies a predicate to filter the stream, retaining only even numbers.

3. evenNumbers.collect(Collectors.toList()) collects the filtered numbers into a list and prints them, showing only the even numbers.

4. Stream.of("apple", "banana", "cherry", "date", "elderberry") creates a stream of fruit names.

5. stringStream.filter(s -> s.length() > 5) filters the stream to include only fruits with names longer than 5 characters.

6. longFruits.collect(Collectors.toList()) collects the results into a list and prints them, showing fruits with names longer than 5 characters.