☕ Core Java Concepts
1. Java Basics
What Java is and how it works
JVM (Java Virtual Machine)
JRE (Java Runtime Environment)
JDK (Java Development Kit)
Platform independence (Write Once, Run Anywhere)
2. Data Types & Variables
Primitive types: int, double, char, boolean, etc.
Non-primitive types: String, arrays, objects
Variable declaration, initialization, and scope
3. Operators
Arithmetic (+, -, *, /)
Relational (==, <, >=)
Logical (&&, ||, !)
Assignment (=, +=, -=)
Unary (++, --)
Ternary operator (condition ? value1 : value2)
4. Control Flow Statements
Conditional:
if, else if, else
switch statements
Looping:
for
while
do-while
Enhanced for-loop (for-each)
Jump Statements:
break
continue
return
5. Object-Oriented Programming (OOP)
Java is heavily OOP-based. Key principles include:
✔ Class & Object
Blueprint vs. instance
Fields (attributes)
Methods (behaviors)
✔ Encapsulation
Hiding data using private variables
Access via getters and setters
✔ Inheritance
Reusing code from parent classes
extends keyword
✔ Polymorphism
Method overloading (compile-time)
Method overriding (runtime)
✔ Abstraction
Abstract classes
Interfaces
6. Constructors
Default constructor
Parameterized constructor
Constructor overloading
this() and super() calls
7. Arrays & Collections
Arrays:
Single-dimensional
Multi-dimensional
Collections Framework:
List, Set, Map
ArrayList, LinkedList
HashMap, TreeMap
HashSet, TreeSet
Iterators
8. Exception Handling
try, catch, finally
Throwing exceptions: throw, throws
Checked vs. unchecked exceptions
Custom exceptions
9. String Handling
Immutable String
Mutable StringBuilder & StringBuffer
Common methods (length(), substring(), replace(), etc.)
10. File Handling (I/O Streams)
Byte streams (FileInputStream, FileOutputStream)
Character streams (FileReader, FileWriter)
Buffered streams
Serialization (Serializable interface)
11. Multithreading & Concurrency
Thread creation (Thread class, Runnable interface)
Thread lifecycle
Synchronization
Locks and concurrent collections
ExecutorService, Future, Callable
12. Java Memory Management
Stack vs. Heap
Garbage Collection
final, finally, finalize differences
13. JDBC (Java Database Connectivity)
Connecting to databases
Executing SQL queries
Connection, Statement, PreparedStatement, ResultSet
14. Java 8+ Features
Lambda expressions
Functional interfaces (Predicate, Function, Consumer)
Streams API
Default & static methods in interfaces
Optional class
Date and Time API (LocalDate, LocalTime, LocalDateTime)
15. Packages & Access Modifiers
Packages:
Default package
User-defined packages
Importing classes
Access Modifiers:
public
private
protected
default (package-private)
16. Important Core Libraries
java.lang
java.util
java.io
java.time
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