How to Use Java 8 Lambda Expressions for Conditional Filtering and Ordering

How can I use Java 8 lambda expressions to filter a List based on specific conditions while maintaining a certain order?

List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "David");
List<String> filteredAndSortedNames = names.stream()
    .filter(name -> name.startsWith("A") || name.startsWith("D"))
    .sorted()
    .collect(Collectors.toList());

In Java 8, the introduction of lambda expressions and the Stream API allowed for more functional programming paradigms. You can easily filter and order collections with concise and readable code using these features.

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

public class Example {
    public static void main(String[] args) {
        List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "David");
        List<String> filteredAndSortedNames = names.stream()
            .filter(name -> name.startsWith("A") || name.startsWith("D"))
            .sorted()
            .collect(Collectors.toList());

        System.out.println(filteredAndSortedNames); // Output: [A, D]
    }
}

Causes

• You need to filter elements in a collection based on certain criteria.
• You want the resulting elements to be ordered in a specific way after filtering.

Solutions

• Utilize the `stream()` method to convert a collection into a stream.
• Apply the `filter()` method to specify the conditions for the elements you want to keep.
• Use the `sorted()` method to arrange the filtered elements in the desired order.
• Finally, use `collect()` to gather the results back into a List or another collection.

Mistake: Not using `sorted()` after `filter()` to order the elements.

Solution: Ensure the `sorted()` method is called after `filter()`, so the processed stream maintains the required order.

Mistake: Forgetting to collect the results back into a List or another collection.

Solution: Use the `collect(Collectors.toList())` method to gather your results after processing the stream.