Java Syntax Basics

Java Syntax

• Variables:
  • Declaration: type variableName;
  • Primitive data types: int, double, boolean, etc.
  • Reference data types: String, Array, etc.
• Operators:
  • Arithmetic operators: +, -, *, /, etc.
  • Comparison operators: ==, !=, >, <, etc.
  • Logical operators: &&, ||, !
• Control Flow:
  • Conditional statements: if, if-else, switch
  • Loops: for, while, do-while
• Methods:
  • Method declaration: returnType methodName(parameters) { ... }
  • Method calling: methodName(arguments)

Object-Oriented Programming (OOP)

• Classes and Objects:
  • Class: a blueprint for creating objects
  • Object: an instance of a class
• Inheritance:
  • A child class inherits properties and behavior from a parent class
  • extends keyword is used to inherit from a parent class
• Polymorphism:
  • Method overriding: a child class provides a different implementation of a method
  • Method overloading: multiple methods with the same name but different parameters
• Encapsulation:
  • Hiding internal implementation details from the outside world
  • Using private variables and public methods to access them

Java Multithreading

• Thread:
  • A separate path of execution within a program
  • Created using Thread class or Runnable interface
• Thread Life Cycle:
  • Newborn: created but not started
  • Runnable: eligible to run
  • Running: executing
  • Dead: finished or terminated
• Synchronization:
  • Using synchronized keyword to ensure thread safety
  • Using wait() and notify() methods to coordinate threads

Exception Handling

• Try-Catch Block:
  • try block: code that may throw an exception
  • catch block: code to handle an exception
• Exception Types:
  • Checked exceptions: must be handled or declared
  • Unchecked exceptions: runtime exceptions, no need to handle or declare
• Throwing Exceptions:
  • Using throw keyword to throw an exception
  • Using throws keyword to declare an exception

Constructor

• Default Constructor:
  • A no-argument constructor provided by the compiler
  • Used to initialize objects when no constructor is defined
• Parameterized Constructor:
  • A constructor with parameters
  • Used to initialize objects with specific values
• Copy Constructor:
  • A constructor that creates a copy of an object
  • Used to create a duplicate object

Java Syntax

• Variables Declaration:
  • Must specify the data type followed by the variable name
  • Syntax: type variableName;
• Primitive Data Types:
  • Examples: int, double, boolean
  • Store a single value
• Reference Data Types:
  • Examples: String, Array
  • Store a reference to an object
• Arithmetic Operators:
  • Used for mathematical operations
  • Examples: +, -, *, /
• Comparison Operators:
  • Used for comparing values
  • Examples: ==, !=, >, <

Object-Oriented Programming (OOP)

• OOP is a programming paradigm that revolves around the concept of objects and classes.
• Key features of OOP include encapsulation, abstraction, inheritance, and polymorphism.
• Encapsulation bundles data and methods that operate on that data within a single unit (class).
• Abstraction exposes only necessary information to the outside world while hiding internal details.
• Inheritance creates a new class based on an existing class.
• Polymorphism allows an object to take on multiple forms.

Exception Handling

• An exception is an event that occurs during the execution of a program that disrupts the normal flow of instructions.
• Types of exceptions include checked exceptions (e.g., IOException) and unchecked exceptions (e.g., NullPointerException).
• Exception handling mechanisms include try-catch block, throw keyword, and throws keyword.

Constructors

• A constructor is a special method that is used to initialize objects when they are created.
• Characteristics of constructors include having the same name as the class, having no return type, and being called when an object is created.
• Types of constructors include default constructor (a constructor with no parameters) and parameterized constructor (a constructor with parameters).

Access Modifiers

• Access modifiers are used to control access to classes, methods, and variables.
• Types of access modifiers include public, private, protected, and default (or package-private).
• Public access allows access from anywhere.
• Private access allows access only within the same class.
• Protected access allows access within the same class and its subclasses.
• Default access allows access within the same package.

Inheritance

• Inheritance is a mechanism that allows one class to inherit the properties and behavior of another class.
• Key concepts include superclass (or parent class), subclass (or child class), and inheritance types.
• Superclass is the class from which another class inherits.
• Subclass is the class that inherits from another class.
• Inheritance types include single inheritance, multilevel inheritance, hierarchical inheritance, and multiple inheritance.

Polymorphism

• Polymorphism is the ability of an object to take on multiple forms.
• Types of polymorphism include method overriding, method overloading, and operator overloading.
• Method overriding is a subclass providing a different implementation of a method already defined in its superclass.
• Method overloading is multiple methods with the same name but different parameters.
• Operator overloading is not supported in Java.

Abstraction

• Abstraction is the concept of showing only necessary information to the outside world while hiding internal details.
• Abstraction in Java includes abstract classes, abstract methods, and interfaces.
• Abstract classes are classes that cannot be instantiated and are used as a base class for other classes.
• Abstract methods are methods that are declared without an implementation.
• Interfaces are abstract classes that define a contract for other classes to implement.