1. Introduction

Filtering a List in Java can be done easily using the Stream API introduced in Java 8. The filter method of the Stream interface takes a Predicate and retains only those elements that satisfy the given predicate, essentially filtering the List based on a condition.

2. Program Steps

1. Create a List of integers.

2. Print the original List.

3. Use the stream() method to convert the List to a Stream.

4. Use the filter() method to filter the Stream based on a condition.

5. Collect the result back into a new List.

6. Print the filtered List.

3. Code Program

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

public class FilterList {

    public static void main(String[] args) {

        // Step 1: Create a List of integers
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        // Step 2: Print the original List
        System.out.println("Original List: " + numbers);

        // Step 3: Convert the List to a Stream
        // Step 4: Use the filter() method to filter the Stream based on a condition
        // Step 5: Collect the result back into a new List
        List<Integer> evenNumbers = numbers.stream()
                                    .filter(n -> n % 2 == 0)
                                    .collect(Collectors.toList());

        // Step 6: Print the filtered List
        System.out.println("Filtered List (Even Numbers): " + evenNumbers);
    }
}

Output:

Original List: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Filtered List (Even Numbers): [2, 4, 6, 8, 10]

4. Step By Step Explanation

Step 1: A List of integers named numbers is created and initialized with numbers from 1 to 10.

Step 2: The original List, numbers, is printed to the console.

Step 3: The List numbers is converted to a Stream using the stream() method.

Step 4: The filter() method is used on the Stream to retain only the even numbers. The filter() method takes a Predicate as an argument, which in this case, is a lambda expression n -> n % 2 == 0 specifying the condition for a number to be even.

Step 5: The filtered Stream is collected back into a new List named evenNumbers using the collect() method and Collectors.toList().

Step 6: Finally, the filtered List containing only even numbers, evenNumbers, is printed to the console.