Core Java Roadmap

-- base level

1. DataTypes & Variables
2. Type Conversion & Casting
3. Operators
4. Conditional Statements
5. Control Structures (loops)
6. Functions & Recursion
7. Arrays
8. Strings & StringBuilder

-- mid level

1. OOPS (class, object, inheritance, polymorphism, abstraction, encapsulation)
2. Constructors
3. Access Modifiers
4. Memory Management (stack, heap, garbage collector)
5. Special Keywords (static, final, this, super, instanceof)
6. Packages
7. Interfaces & Abstract Classes
8. Collections (List, Set, Map, Generics)
9. Enums
10. Exception Handling

-- advance level

1. Streams API (map, filter, reduce)
2. Functional Programming (lambdas, method references, functional interfaces)
3. Multithreading & Concurrency
4. File Handling (I/O, NIO)
5. Serialization & Deserialization
6. Annotations & Reflection
7. JDBC Basics
8. Unit Testing (JUnit)

-- optional mastery

1. Java 8+ Features (Optional, Date/Time API, default methods in interfaces)
2. JVM Internals (class loading, JIT compiler, bytecode)
3. Design Patterns (Singleton, Factory, Observer, etc.)