Java Streams | What is the difference between sorted() and distinct() in streams?

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sorted()

The sorted() method is used to sort the elements of a stream. It orders the elements based on their natural ordering or a custom comparator.

Key Characteristics:

Returns a sorted stream of elements.
Does not eliminate duplicates (it retains all elements).
Can use natural ordering or a custom comparator.

Example 1: Natural Ordering

List<Integer> numbers = List.of(4, 2, 3, 1, 4);
List<Integer> sortedList = numbers.stream()
                                  .sorted()
                                  .collect(Collectors.toList());
System.out.println(sortedList); // Output: [1, 2, 3, 4, 4]

Example 2: Custom Ordering

List<String> names = List.of("Charlie", "Alice", "Bob");
List<String> sortedNames = names.stream()
                                .sorted((a, b) -> b.compareTo(a)) // Reverse order
                                .collect(Collectors.toList());
System.out.println(sortedNames); // Output: [Charlie, Bob, Alice]

2. distinct()

The distinct() method is used to remove duplicate elements from a stream. It retains only unique elements based on the result of their equals() method.

Key Characteristics:

Eliminates duplicates from the stream.
Retains the original order of elements (stable).
Relies on the implementation of equals() for determining uniqueness.

Example: Removing Duplicates

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

Example Combining sorted() and distinct()

You can use both methods together to first remove duplicates and then sort the remaining elements.

List<Integer> numbers = List.of(4, 2, 3, 1, 4);
List<Integer> result = numbers.stream()
                              .distinct() // Remove duplicates
                              .sorted()   // Sort the unique elements
                              .collect(Collectors.toList());
System.out.println(result); // Output: [1, 2, 3, 4]

When to Use Each?

Use sorted() when you want to order the elements in a specific sequence.
Use distinct() when you want to ensure there are no duplicates in your stream.
Both methods can be combined when your use case requires removing duplicates and sorting the resulting elements.