1. Introduction to Java

Java was developed by Sun Microsystems in 1995. It is used for building cross-platform applications, from web apps to mobile apps and large-scale enterprise systems.

2. Basic Syntax

Java syntax is similar to other C-based languages but with some unique features. Here are some basic elements of Java syntax:

• Class Definition:Every Java application must have at least one class, which is a blueprint for creating objects.
• Main Method:Themainmethod is the entry point of any Java application. It must be declared aspublic static void main(String[] args).
• Comments:Use//for single-line comments and/* ... */for multi-line comments.

3. Basic Structure of a Java Program

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

4. Variables and Data Types

Variables store data values, and Java is a statically-typed language, meaning you must declare the type of a variable. Common data types include:

• Primitive Data Types:
  • int: Integer numbers (e.g.,int age = 30;)
  • double: Floating-point numbers (e.g.,double price = 19.99;)
  • char: Single characters (e.g.,char grade = 'A';)
  • boolean: True or false values (e.g.,boolean isJavaFun = true;)
• Reference Data Types:
  • String: Sequence of characters (e.g.,String name = "John";)
  • Arrays: Collections of elements (e.g.,int[] numbers = {1, 2, 3};)

5. Operators

Java operators are used to perform operations on variables and values. Common operators include:

• Arithmetic Operators:+,-,*,/,%
• Relational Operators:==,!=,>,<,>=,<=
• Logical Operators:&&(AND),||(OR),!(NOT)
• Assignment Operators:=,+=,-=,*=,/=

6. Control Flow Statements

Control flow statements determine the direction of execution of code. Common control flow statements include:

• Conditional Statements:
  • if: Executes a block of code if its condition is true.
  • else: Executes a block of code if theifcondition is false.
  • switch: Allows multi-way branching based on the value of a variable.
• Loops:
  • for: Repeats a block of code a specific number of times.
  • while: Repeats a block of code as long as its condition is true.
  • do-while: Repeats a block of code at least once and then continues based on a condition.

7. Methods

Methods are blocks of code that perform a specific task and can be called to execute. They help to organize and reuse code.

public class Calculator {
    public static int add(int a, int b) {
        return a + b;
    }

    public static void main(String[] args) {
        int result = add(5, 3);
        System.out.println("Sum: " + result);
    }
}

8. Object-Oriented Programming Concepts

Java is an object-oriented language, and it includes several key concepts:

• Classes and Objects:A class is a blueprint for objects, and objects are instances of classes.
• Inheritance:Allows a class to inherit properties and methods from another class.
• Encapsulation:Hides the internal state of an object and only exposes a controlled interface.
• Polymorphism:Allows methods to do different things based on the object’s type.
• Abstraction:Hides complex implementation details and shows only the necessary features.

9. Exception Handling

Exception handling allows a program to handle runtime errors gracefully. Java usestry,catch, andfinallyblocks for exception handling.

try {
    // Code that may throw an exception
} catch (ExceptionType e) {
    // Code to handle the exception
} finally {
    // Code that will always execute
}

10. Basic Java I/O

Java provides several classes for handling input and output. Common classes include:

• Scanner:For reading input from various sources.
• PrintWriter:For writing formatted text to files or other outputs.
• File:For creating, deleting, and managing files and directories.