This table is designed for zero-to-hero learners. It blends core concepts + practical uses + real-world analogies + mnemonics so you can quickly revise and apply them.
| Topic | Why & When We Use It | Real-Life Analogy | Examples (Daily Life / Android Apps / Cybersecurity) | Mnemonic (ISO-Style) |
|---|---|---|---|---|
| Collections | To group multiple objects into one unit and manage them efficiently | Like a toolbox holding different tools | Daily life: Shopping bag holding items. Android: Contacts list grouped. Cybersecurity: Bundling logs/events. |
COLL → Container Of Lots of Lists |
| List | Ordered collection, allows duplicates | Queue at a ticket counter | Daily: To-do list in order. Android: Music playlist. Cyber: Ordered attack logs. |
LIST → Linearly Indexed Set of Things |
| ArrayList | Resizable array, fast access, slow inserts/deletes | Dynamic shelf expanding when needed | Daily: Expanding notebook. Android: Gallery images. Cyber: Storing IP addresses quickly. |
ARRL → Auto-Resize Retrieval List |
| LinkedList | Fast insertion/deletion, slower access | Chain of people linked hand-in-hand | Daily: Train coaches linked. Android: Messaging threads. Cyber: Packet hops in a route. |
LINK → Links In Nodes Kept |
| List Sorting | To arrange items for efficiency | Books sorted on a shelf | Daily: Phone contacts A→Z. Android: Sorting search results. Cyber: Sort by threat level. |
SORT → Structure Ordered Rank Table |
| Set | Unique elements, no duplicates | Bag of unique coins | Daily: Student roll numbers. Android: Unique installed apps. Cyber: Unique device IDs. |
SET → Stores Elements Trimmed |
| HashSet | Fast access, no order | Box with labels for fast retrieval | Daily: Storing friends’ phone numbers uniquely. Android: Caching unique tokens. Cyber: Unique IP blacklist. |
HSET → Hash for SET uniqueness |
| TreeSet | Sorted unique elements | Sorted drawer of files | Daily: Sorted exam roll numbers. Android: Sorted notifications. Cyber: Sorted vulnerabilities list. |
TSET → Tree-structured SET |
| LinkedHashSet | Unique elements + insertion order | Guestbook with unique signatures | Daily: First-come-first-served entries. Android: Recent searches (unique, ordered). Cyber: Ordered list of logged attacks. |
LHSET → Linked History of SET |
| Map | Key–Value pair storage | Dictionary (word → meaning) | Daily: Name → Phone number. Android: SharedPreferences key-value storage. Cyber: IP → Threat level mapping. |
MAP → Matches Associated Pairs |
| HashMap | Fast lookup by key | Warehouse with labeled boxes | Daily: ID → Student name. Android: Store app configs. Cyber: SessionID → User details. |
HMAP → Hash-based MAP |
| TreeMap | Sorted key–value pairs | Library catalog system | Daily: Contacts sorted by names. Android: Sorted settings. Cyber: Sort exploits by severity. |
TMAP → Tree-structured MAP |
| LinkedHashMap | Maintains insertion order of key–value | Chronological diary with entries | Daily: To-do tasks by order added. Android: Browser history. Cyber: Ordered login attempts. |
LHMAP → Linked History MAP |
| Iterator | To traverse collections safely | Tour guide leading step by step | Daily: Turning book pages. Android: Iterating chat messages. Cyber: Scanning logs one by one. |
ITER → Iterative Traversal Element Reader |
| Algorithms | To solve problems efficiently (search, sort, optimize) | Cooking recipe (step-by-step) | Daily: Searching keys at home. Android: Searching songs in Spotify. Cyber: Searching vulnerabilities. |
ALG → Algorithm = Logic Guide |
- Start with Lists & Sets → Get comfy with basics.
- Move to Maps → Learn key-value storage.
- Master Iterators & Sorting → Control flow + efficiency.
- Apply Algorithms → Problem-solving mindset.
💡 Remember: Data Structure = HOW we store | Algorithm = HOW we solve.