Collections refer to the java.util package's classes and interfaces for storing and managing various objects. They provide flexible ways to work with data sets, providing functions such as adding, removing, and accessing objects. Object compilations in Java are broadly divided into interfaces and classes that implement these interfaces.

 

Key Interfaces in Java Collections

 

List- Represents an ordered collection of elements, where each element is indexed starting at 0.

List<String> list = new ArrayList<>();
list.add("Java");
list.add("Python");
list.add("C++");
System.out.println(list); // Output: [Java, Python, C++]

 

Set It represents a collection that does not allow duplicate elements.

Set<String> set = new HashSet<>();
set.add("Apple");
set.add("Orange");
set.add("Apple"); // Duplicate "Apple" will not be added
System.out.println(set); // Output: [Orange, Apple]

 

Map- It represents a collection of key-value pairs where each key is unique.

Map<String, Integer> map = new HashMap<>();
map.put("One", 1);
map.put("Two", 2);
map.put("Three", 3);
System.out.println(map.get("Two")); // Output: 2

 

Queue- It represents a collection designed to hold elements prior to processing, typically in FIFO (first-in-first-out) order.

Queue<String> queue = new LinkedList<>();
queue.add("First");
queue.add("Second");
queue.add("Third");
System.out.println(queue.poll()); // Output: First (removes and returns the head of the queue)

 

Classes Implementing Collection Interfaces

 

ArrayList- It implements the List interface using a dynamic array.

List<String> list = new ArrayList<>();
list.add("Java");
list.add("Python");
list.add("C++");

 

HashSet- It implements the Set interface using a hash table.

Set<String> set = new HashSet<>();
set.add("Apple");
set.add("Orange");

 

HashMap- It implements the Map interface using a hash table for key-value pairs.

Map<String, Integer> map = new HashMap<>();
map.put("One", 1);
map.put("Two", 2);

 

LinkedList-  It implements the List and Queue interfaces using a doubly-linked list.

Queue<String> queue = new LinkedList<>();
queue.add("First");
queue.add("Second");

 

Utility Classes

 

Collections- It provides static methods for operating on collections, such as sorting and searching.

List<String> list = new ArrayList<>();
list.add("Java");
list.add("Python");
list.add("C++");
Collections.sort(list); // Sorts the list

 

Benefits of Using Collections

Flexibility- Collections provide multiple ways of storing and manipulating objects.

Efficiency- Specialized implementations such as HashMap and HashSet provide efficiency.

Type Safety- Generics ensure type safety, preventing runtime errors.

Understanding and using these Java collections properly is essential to developing efficient and robust applications in Java. Each collection has its advantages, so choosing the right one depends on the specific requirements of your application.

 

Also, Read: Security Best Practices for Java Applications