Skip to content

Java Review Notes

Basics

  • JVM (Java Virtual Machine): Executes Java bytecode
  • JDK (Java Development Kit): Contains tools for developing Java applications
  • JRE (Java Runtime Environment): Provides libraries and JVM for running Java applications

Data Types

  • Primitive Types: int, double, char, boolean, float, long, short, byte
  • Reference Types: Objects, Arrays, Strings, etc

Variables

  • Local: Declared inside methods or blocks
  • Instance: Belong to instances of a class
  • Static: Belong to the class itself

Control Flow

  • Conditionals: if, else if, else, switch
  • Loops: for, while, do-while
  • Break/Continue: Control loop execution

Object-Oriented Programming

  • Class: Blueprint for objects
  • Object: Instance of a class
  • Inheritance: class SubClass extends SuperClass
  • Polymorphism: Method overriding and overloading
  • Encapsulation: Use private fields with public getters/setters
  • Abstraction: Abstract classes and interface

Access Modifiers

  • public: Accessible everywhere
  • protected: Accessible in the same package or subclasses
  • default: Accessible within the same package
  • private: Accessible only within the class

Key Concepts

  • Constructors: Special methods to initialize objects
  • this Keyword: Refers to the current object
  • super Keyword: Refers to the parent class
  • Static Methods/Variables: Belong to the class, not instances
  • Final Keyword: Used to declare constants, prevent inheritance, or prevent method overriding

Collections

  • List: ArrayList, LinkedList
  • Set: HashSet, TreeSet
  • Map: HashMap, TreeMap

Exception Handling

  • Try-Catch: Handle exceptions
  • Finally: Code that always executes
  • Throws: Declare exceptions
  • Throw: Manually throw exceptions

Input/Output

  • Scanner: For user input
  • BufferedReader: For efficient reading
  • File: For handling files

Miscellaneous

  • toString(): Converts objects to strings
  • equals(): Compares object content
  • hashCode(): Returns hash code
  • Lambda Expressions: Concise way to express instances of single-method interfaces
  • Streams: Process sequences of elements with functional-style operations