SrcForge

Lesson 36

Java Collections Framework

JCF provides ready-to-use data structures. List, Set, Queue, Map — all built-in.

Java Track

Save progress as you learn.

61 lessons

Lesson content

JCF stores and processes object groups efficiently.

Key Terms

  • Collection: Object storing a group of elements.
  • List: Ordered, allows duplicates.
  • Set: No duplicates allowed.
  • Queue: FIFO order processing.
  • Map: Key-value pair storage.

Framework Hierarchy

Iterable
   │
Collection
   ├── List → ArrayList, LinkedList, Vector
   ├── Set  → HashSet, LinkedHashSet, TreeSet
   └── Queue → PriorityQueue, LinkedList

Map → HashMap, LinkedHashMap, TreeMap

Example: ArrayList

import java.util.ArrayList;

public class ArrayListExample {
    public static void main(String[] args) {
        ArrayList<String> fruits = new ArrayList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Apple");
        System.out.println(fruits);
    }
}
[Apple, Banana, Apple]

Example: HashSet

import java.util.HashSet;

public class HashSetExample {
    public static void main(String[] args) {
        HashSet<String> fruits = new HashSet<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Apple");
        System.out.println(fruits);
    }
}
[Apple, Banana]

Example: PriorityQueue

import java.util.PriorityQueue;

public class QueueExample {
    public static void main(String[] args) {
        PriorityQueue<Integer> queue = new PriorityQueue<>();
        queue.add(30);
        queue.add(10);
        queue.add(20);
        while (!queue.isEmpty()) {
            System.out.println(queue.poll());
        }
    }
}
10
20
30

Example: HashMap

import java.util.HashMap;

public class HashMapExample {
    public static void main(String[] args) {
        HashMap<Integer, String> students = new HashMap<>();
        students.put(101, "John");
        students.put(102, "Alice");
        students.put(103, "David");
        System.out.println(students);
    }
}
{101=John, 102=Alice, 103=David}

Iterating Collections

for (String name : names) {
    System.out.println(name);
}

Collection vs Collections

  • Collection: Interface for grouping objects.
  • Collections: Utility class with sort, search methods.

FAQ

1. What is JCF?

Interfaces and classes for managing object groups.

2. List vs Set?

List allows duplicates. Set stores unique only.

3. HashMap vs HashSet?

HashMap stores key-value pairs. HashSet stores values only.

JCF provides built-in data structures.
List allows duplicates, Set does not.
Queue follows FIFO order.
Map stores key-value pairs.
ArrayList — fast access, allows duplicates.
HashMap — fast key-value lookup.
Use interfaces, not implementation classes.

Where Java is used

Java in real-world development

List

Ordered, allows duplicates. ArrayList for fast access, LinkedList for fast insert.

Set

No duplicates. HashSet unordered, TreeSet sorted.

Queue

FIFO processing. PriorityQueue sorts by natural order.

Map

Key-value pairs. Keys unique. HashMap fast, TreeMap sorted.

Collection vs Collections

Collection is interface. Collections is utility class with sort/search.

Best Practice

Use List<String> not ArrayList<String>. Program to interface.

Prev: Java Stream APIBack to hub