Week 4 — Java Collections, JDBC, MongoDB, NoSQL & AWS

[Collections] What is the Java Collections Framework?

Interfaces and classes for storing and manipulating groups of objects, including List, Set, Queue and Map.

[Collections] What is the difference between List and Set?

List preserves element positions and allows duplicates; Set enforces uniqueness.

[Collections] What is ArrayList versus LinkedList?

ArrayList uses a resizable array with fast indexed access; LinkedList uses nodes and has slower indexed traversal.

[Collections] What is HashMap versus Hashtable?

HashMap is generally unsynchronized and permits one null key; Hashtable is legacy synchronized and rejects null keys and values.

[Collections] What is HashSet?

A Set implementation backed by hashing that offers expected constant-time add and contains operations.

[Collections] What is the difference between array and ArrayList?

Arrays have fixed length accessed by length; ArrayLists resize dynamically and use size().

[Collections] How do you remove duplicates while preserving insertion order?

Construct a LinkedHashSet from the collection, then convert it back to a List if needed.

[Database Theory] What is a primary key?

A column or set of columns uniquely identifying each row and disallowing null key values.

[Database Theory] What is a foreign key?

A column or columns referencing a candidate key in another or the same table to enforce referential integrity.

[Database Theory] What is database normalization?

Structuring relations to reduce redundancy and update anomalies.

[Database Theory] What are 1NF, 2NF and 3NF?

1NF requires atomic column values; 2NF removes partial dependency on composite keys; 3NF removes transitive dependencies of non-key attributes.

[Database Theory] What is an index?

A data structure accelerating lookups and sorts at the cost of storage and write maintenance.

[Database Theory] What is an ER diagram?

A conceptual diagram of entities, attributes and relationships in a data model.

[JDBC] What is JDBC?

Java Database Connectivity is a standard API for connecting to relational databases and executing SQL.

[JDBC] What is a PreparedStatement?

A precompiled parameterized SQL statement that helps prevent SQL injection and supports parameter binding.

[JDBC] What is ResultSet?

An object representing rows returned by a JDBC query.

[JDBC] What is a connection pool?

A reusable collection of database connections that avoids opening a new connection for each request.

[JDBC] What is the difference between executeQuery and executeUpdate?

executeQuery returns a ResultSet for queries; executeUpdate returns an update count for DML or certain DDL.

[JDBC] How do you manage JDBC resources?

Use try-with-resources to close connections, statements and result sets reliably.

[NoSQL Introduction] What is NoSQL?

A broad category of non-relational data models, including document, key-value, column-family and graph databases.

[NoSQL Introduction] When choose NoSQL over relational SQL?

When flexible schemas, specialized access patterns or horizontal scaling fit requirements better than relational joins and constraints.

[NoSQL Introduction] What is a document database?

A database storing structured documents, commonly JSON-like objects, with nested fields.

[NoSQL Introduction] What is horizontal scaling?

Increasing capacity by adding machines rather than only increasing resources on one machine.

[NoSQL Introduction] What is eventual consistency?

Replicas may temporarily disagree after writes but converge under normal operation.

[MongoDB Concepts] What is MongoDB?

A document-oriented database storing BSON documents in collections.

[MongoDB Concepts] What is the difference between a collection and a document?

A collection groups documents; a document is a structured record of fields and values.

[MongoDB Concepts] What is BSON?

A binary representation of JSON-like documents supporting additional data types.

[MongoDB Concepts] What is the _id field?

A unique identifier for each MongoDB document, often generated as an ObjectId.

[MongoDB Concepts] What is an aggregation pipeline?

A sequence of stages that filters, groups, transforms and summarizes documents.

[MongoDB Concepts] What is a MongoDB index?

A data structure that speeds matching and sorting but adds storage and write overhead.

[MongoDB Shell] How do you insert a MongoDB document?

Use db.collection.insertOne({name: "Ana"}) or insertMany for multiple documents.

[MongoDB Shell] How do you find documents in MongoDB?

Use db.collection.find({field: value}) with optional projection and sort.

[MongoDB Shell] How do you update one document?

Use db.collection.updateOne(filter, {$set: {field: value}}).

[MongoDB Shell] How do you delete one document?

Use db.collection.deleteOne(filter).

[MongoDB Shell] How do you count matching documents?

Use db.collection.countDocuments(filter).

[MongoDB Shell] How do you create an index?

Use db.collection.createIndex({field: 1}) for an ascending index.

[Java Reflection] What is Java reflection?

A runtime API for inspecting classes, methods, fields and annotations, and optionally invoking or modifying them.

[Java Reflection] How do you get a Class object?

Use Object.getClass(), Type.class or Class.forName with a fully qualified class name.

[Java Reflection] Why do frameworks use reflection?

To discover annotated components, inspect metadata and instantiate or invoke types dynamically.

[Java Reflection] What are reflection drawbacks?

It can weaken encapsulation, add overhead and shift errors from compile time to runtime.

[Java Time] What is java.time?

Java's modern date-time API for immutable date, time, duration and time-zone types.

[Java Time] What is LocalDate versus LocalDateTime?

LocalDate stores a calendar date; LocalDateTime stores a date and time without time-zone information.

[Java Time] What is Instant?

A point on the UTC timeline useful for timestamps.

[Java Time] What is ZonedDateTime?

A date-time associated with a time-zone region and its rules.

[Java Time] Why prefer java.time over Date and Calendar?

It has clearer immutable types and more predictable time-zone handling.

[AWS Introduction (Week 4)] What is cloud computing?

On-demand access to computing resources with elastic capacity and usage-based billing.

[AWS Introduction (Week 4)] What is IaaS versus PaaS versus SaaS?

IaaS provides infrastructure, PaaS provides managed application platforms, and SaaS delivers complete software.

[AWS Introduction (Week 4)] What is the difference between scaling up and scaling out?

Scaling up adds resources to one machine; scaling out adds more machines.

[AWS Introduction (Week 4)] What is an AWS Region versus Availability Zone?

A Region is a geographic area; an AZ is an isolated infrastructure location within that Region.