? Collections Utility Class

? Quick Overview

The Collections utility class in Java is part of the java.util package. It provides static methods to operate on collection objects such as sorting, searching, reversing, synchronizing, and making collections unmodifiable.

? Key Concepts

Contains only static methods
Works with List, Set, and Map
Helps reduce manual algorithm code
Improves readability and reliability

? Syntax / Theory

The Collections class cannot be instantiated. All methods are accessed using the class name.

? View Code Example

// Importing Collections utility class
import java.util.Collections;
import java.util.List;

? Code Example(s)

? View Code Example

// Demonstrating common Collections utility methods
import java.util.*;

public class CollectionsDemo {
public static void main(String[] args) {

List numbers = new ArrayList<>();

numbers.add(40);
numbers.add(10);
numbers.add(30);
numbers.add(20);

Collections.sort(numbers);
System.out.println(numbers);

Collections.reverse(numbers);
System.out.println(numbers);

int index = Collections.binarySearch(numbers, 20);
System.out.println(index);
}
}

? Live Output / Explanation

Output Explanation

sort() arranges elements in ascending order
reverse() reverses the current order
binarySearch() finds the index of an element

? Interactive Collections Playground

Click the buttons to visualize how Java methods affect a List.

> Ready. Waiting for command...

? Tips & Best Practices

Always use generics to avoid ClassCastException
Use Collections.unmodifiableList() for read-only data
Prefer utility methods over custom algorithms

? Try It Yourself

Create a list of strings and sort alphabetically
Find maximum and minimum elements using Collections
Convert a list into a synchronized list