[Java] Java Primer: Types, Classes, and Operators

📋 Here are the notes summarizing what I learned from the course!

Java Compiler

Definition

Java is a compiled language, meaning programs are first compiled into bytecode and then executed by the Java Virtual Machine (JVM).

Source Code (.java) → Bytecode (.class) → Executed by JVM

Components of a Java Program

Definition

In Java, the basic building block is the class, which contains methods (functions). The main method is the entry point for any Java application.

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

Identifiers

Definition

Identifiers are the names used for classes, methods, and variables in Java. They must start with a letter and can include numbers.

int number;
String name;

Base Types

Definition

Java has several primitive data types used for storing simple values directly.

int age = 30;
double price = 19.99;
boolean isActive = true;

Classes and Objects

Definition

A class in Java can be thought of as a blueprint for creating objects (instances).

public class Bicycle {
    int gear;
    int speed;

    void changeGear(int newGear){
        gear = newGear;
    }

    void speedUp(int increment){
        speed += increment;
    }
}

Creating and Using Objects

Definition

Objects are instances of classes created with the new keyword.

Bicycle myBike = new Bicycle();
myBike.changeGear(3);
myBike.speedUp(10);

Wrapper Types and Boxing

Definition

Java uses wrapper classes for all primitive types to facilitate operations in object-based contexts.

Integer myInt = 5; // Auto-boxing
int x = myInt;     // Auto-unboxing

Method Signatures

Definition

The signature of a method in Java includes its name and parameter types, which helps in identifying the correct method to execute.

public void greet(String name) {
    System.out.println("Hello, " + name);
}

Operators

Definition

Java supports various operators for arithmetic, logical operations, and more.

int result = 1 + 2; // Addition
boolean isTrue = (result == 3);

Control Structures

Definition

Java provides control structures such as if-else statements, loops, and switch cases for controlling the flow of execution.

if (isTrue) {
    System.out.println("Result is 3");
} else {
    System.out.println("Result is not 3");
}

for (int i = 0; i < 5; i++) {
    System.out.println(i);
}

Input and Output

Definition

Java uses System.out for output and System.in with a Scanner for input.

Scanner scanner = new Scanner(System.in);
System.out.print("Enter your name: ");
String name = scanner.nextLine();
System.out.println("Hello, " + name);

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