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  • Writer's pictureSatheesh K

Data Structures and Collections in Java

Data Structures in Java refer to the systematic ways of organizing, storing, and managing data within a computer program. These structures enable efficient operations like insertion, deletion, retrieval, and traversal. Some common data structures in Java include:

  1. Arrays: A fixed-size collection of elements of the same type. int[] numbers = { 1, 2, 3, 4, 5 };

  2. ArrayList: A dynamic array that can grow or shrink. import java.util.ArrayList; // ... ArrayList<String> names = new ArrayList<>(); names.add("Alice"); names.add("Bob");

  3. LinkedList: A linear data structure where elements are connected via pointers. import java.util.LinkedList; // ... LinkedList<Integer> linkedList = new LinkedList<>(); linkedList.add(10); linkedList.add(20);

  4. Stack: A last-in, first-out (LIFO) structure. import java.util.Stack; // ... Stack<Character> stack = new Stack<>(); stack.push('A'); stack.push('B');

  5. Queue: A first-in, first-out (FIFO) structure. import java.util.Queue; import java.util.LinkedList; // ... Queue<String> queue = new LinkedList<>(); queue.add("Apple"); queue.add("Banana");

  6. HashMap: A key-value pair data structure. import java.util.HashMap; // ... HashMap<String, Integer> ages = new HashMap<>(); ages.put("Alice", 30); ages.put("Bob", 25);

  7. HashSet: A set of unique elements. import java.util.HashSet; // ... HashSet<String> uniqueNames = new HashSet<>(); uniqueNames.add("Alice"); uniqueNames.add("Bob");

  8. TreeMap: A sorted map based on a binary search tree. import java.util.TreeMap; // ... TreeMap<Integer, String> sortedMap = new TreeMap<>(); sortedMap.put(3, "C"); sortedMap.put(1, "A");

  9. Graph: A non-linear data structure with vertices and edges.

  10. Trie: A prefix tree for efficient string matching.

A collection is a higher-level concept in Java that builds upon data structures. The Java Collections Framework (JCF) offers a rich set of pre-built collection implementations like ArrayList, LinkedList, HashSet, HashMap, etc.

These collections are built on underlying data structures (e.g., ArrayList uses an array internally).

Pic courtesy to beginnersBook.coom. Please follow the link for examples - Collections in Java with Example Programs (

Here's an analogy:

  • Think of a data structure as a filing cabinet. It defines how folders and documents are physically organized within the cabinet.

  • A collection is like a set of labels you stick on the folders. These labels (the JCF interface) provide a standard way to access and manage the documents (objects) inside the cabinet (data structure).

Here's a table summarizing the key differences:


Data Structure



How data is organized in memory

How to access and manipulate groups of objects


No standard interface

Provides a standard interface (methods)


Can be custom-built or use built-in options

Pre-built implementations in Java Collections Framework (JCF)


Array, Linked List, Stack, Queue, Tree, Graph

ArrayList, LinkedList, HashSet, HashMap, etc.

In essence:

  • Data structures are the building blocks for efficient data organization.

  • Collections provide a standardized way to work with these data structures in Java.

Content courtesy to and

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