Java Interview Question: Sort a List Using Streams (Ascending & Descending Order)

 

🔹 Introduction

Sorting is one of the most fundamental operations in programming and is frequently asked in Java interviews.

👉 In this article, we will learn how to sort a list using:

• Traditional approach
• Java Streams (modern approach)

---

🔹 Problem Statement

Given a list of integers, sort it in ascending and descending order.

Example:

Input: [5, 2, 8, 1, 3]  
Output: Ascending: [1, 2, 3, 5, 8]  
Descending: [8, 5, 3, 2, 1]  

---

🔹 Approach 1: Using Collections.sort()

💡 Explanation

• Use built-in sorting method
• Works directly on list

---

👨‍💻 Java Code

import java.util.*;

public class SortList {
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(5,2,8,1,3);

        Collections.sort(list);
        System.out.println("Ascending: " + list);

        Collections.sort(list, Collections.reverseOrder());
        System.out.println("Descending: " + list);
    }
}

---

🔹 Approach 2: Using Java Streams (Recommended)

💡 Explanation

• Use sorted() method
• Use comparator for descending

---

👨‍💻 Java Code (Streams)

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

public class SortList {
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(5,2,8,1,3);

        List<Integer> asc = list.stream()
                                .sorted()
                                .toList();

        List<Integer> desc = list.stream()
                                 .sorted(Comparator.reverseOrder())
                                 .toList();

        System.out.println("Ascending: " + asc);
        System.out.println("Descending: " + desc);
    }
}

---

🔹 Output

Ascending: [1, 2, 3, 5, 8]  
Descending: [8, 5, 3, 2, 1]  

---

🔹 Time Complexity

• O(n log n)

---

🔹 Key Takeaways

✔ sorted() is key method in streams
✔ Comparator helps customize sorting
✔ Very common interview question

---

🔹 Conclusion

Sorting using Streams is clean and efficient.
Make sure you understand both approaches for interviews.

---

🔗 Also Read

👉 First Non-Repeating Character in Java
👉 Check Palindrome String in Java
👉 Reverse a String
👉 Count Character Frequency in Java

👉 Find Duplicate Characters in a String