📊 Java List Sorting – Complete Guide with Syntax, Comparators & Best Practices

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🧲 Introduction – Why List Sorting Matters in Java

Whether you’re building a shopping cart, leaderboard, or contact list — sorting is essential. Java offers multiple ways to sort a list using built-in methods and custom logic for advanced ordering.

With the power of the Collections Framework, Lambdas, and Comparators, Java makes it easy to sort lists by names, numbers, dates, or even complex objects.

By the end of this guide, you’ll learn:

✅ How to sort a Java List in ascending and descending order
✅ How to use Collections.sort() and List.sort()
✅ How to sort custom objects with Comparator and Lambdas
✅ Performance tips and best practices

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🔑 What Is List Sorting in Java?

📊 Sorting a List in Java means arranging its elements in a specific order (natural or custom), using utilities from the Collections or List interface.

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🧪 1. Sorting a List of Strings

import java.util.*;

public class SortStrings {
    public static void main(String[] args) {
        List<String> names = Arrays.asList("John", "Alice", "Bob");
        Collections.sort(names); // Ascending
        System.out.println(names); // [Alice, Bob, John]
    }
}

✅ Collections.sort() sorts the list in natural (alphabetical) order

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🔄 Descending Order

names.sort(Collections.reverseOrder());
System.out.println(names); // [John, Bob, Alice]

✅ Use reverseOrder() for descending sort

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🔢 2. Sorting a List of Integers

List<Integer> numbers = Arrays.asList(5, 1, 3, 9);
Collections.sort(numbers);
System.out.println(numbers); // [1, 3, 5, 9]

📘 Java uses natural order (ascending) for numbers

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🧱 3. Sorting Custom Objects (e.g., Students)

🧩 Using Comparator Class

class Student {
    String name;
    int age;

    Student(String n, int a) {
        name = n;
        age = a;
    }

    public String toString() {
        return name + " (" + age + ")";
    }
}

List<Student> list = new ArrayList<>();
list.add(new Student("Ravi", 23));
list.add(new Student("Aman", 21));
list.add(new Student("Sneha", 22));

// Sort by age
list.sort(Comparator.comparingInt(s -> s.age));
System.out.println(list); // [Aman (21), Sneha (22), Ravi (23)]

✅ Comparator.comparingInt() is concise and readable
✅ You can also use Collections.sort(list, comparator)

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🧠 Sort by Name (String Field)

list.sort(Comparator.comparing(s -> s.name));

✅ Alphabetical sorting by name using Lambda

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🔁 Sort in Descending Order

list.sort(Comparator.comparingInt((Student s) -> s.age).reversed());

✅ Add .reversed() to any comparator

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📦 Collections.sort() vs List.sort()

Method	Available Since	Source	Notes
Collections.sort()	Java 1.2	java.util.Collections	Static method, requires List as parameter
List.sort()	Java 8	List interface	Uses lambda, cleaner, more modern

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🧪 4. Sorting with Streams (Java 8+)

list.stream()
    .sorted(Comparator.comparing(s -> s.name))
    .forEach(System.out::println);

✅ Non-destructive sort — use when you don’t want to modify original list

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📘 Real-World Use Case: Sorting Products by Price

class Product {
    String name;
    double price;

    Product(String name, double price) {
        this.name = name;
        this.price = price;
    }

    public String toString() {
        return name + ": $" + price;
    }
}

List<Product> products = Arrays.asList(
    new Product("Phone", 799.99),
    new Product("Laptop", 1200.0),
    new Product("Tablet", 450.0)
);

products.sort(Comparator.comparingDouble(p -> p.price));
System.out.println(products);

✅ Sorts the product list by price in ascending order

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💡 Best Practices for List Sorting

✅ Use Comparator.comparing() and Lambdas for cleaner code
✅ Prefer List.sort() for modern Java (Java 8+)
✅ Use .reversed() to flip sorting order
✅ Use stream().sorted() for non-destructive sorting
✅ Avoid null values unless explicitly handled in comparator

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✅ Summary

• Java provides powerful tools to sort any type of List
• Use List.sort() or Collections.sort() for in-place sorting
• Leverage Comparator, Lambdas, and Streams for custom sorting logic
• Use .reversed(), thenComparing(), and nullsFirst() for advanced control

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❓ FAQs – Java List Sorting

❓ How do I sort a list in descending order?

Use .sort(Collections.reverseOrder()) or Comparator.reversed()

❓ What if the list contains null values?

Use a comparator like:

Comparator.nullsLast(Comparator.comparing(...))

❓ Can I sort by multiple fields?

Yes. Use thenComparing():

list.sort(Comparator.comparing(Student::getAge).thenComparing(Student::getName));

❓ Does sorting modify the original list?

Yes — Collections.sort() and List.sort() sort in place.
Use Streams if you want to keep the original list unchanged.

❓ What is the default sort order?

Java sorts strings alphabetically and numbers ascendingly by default.

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