Approach 1: Using Stream.distinct()

import java.util.*;
import java.util.stream.*;

List<Integer> nums = Arrays.asList(1,2,2,3,3,3,4);
List<Integer> distinct = nums.stream()
                             .distinct()
                             .collect(Collectors.toList());
System.out.println(distinct); // [1, 2, 3, 4]

Why it works:

• distinct() uses the equals() and hashCode() methods to filter duplicates.
• It preserves the encounter order of the first occurrences.

Approach 2: Using LinkedHashSet (Alternative)

List<Integer> nums = Arrays.asList(1,2,2,3,3,3,4);
List<Integer> distinct = new ArrayList<>(new LinkedHashSet<>(nums));
System.out.println(distinct); // [1, 2, 3, 4]

Why it works:

• LinkedHashSet automatically removes duplicates.
• Preserves insertion order.
• Alternative to streams for cases where you want collection-based deduplication.