title	description	language
Java Basics Examples	A collection of small Java programs demonstrating variables, conditionals, loops, methods, strings, input handling, and recursion.	Java

Java Basics Examples

Overview

This repository contains a set of concise Java classes that illustrate core programming concepts:

• Variables and primitives/reference types (Main)
• Conditional logic and the ternary operator (Conditonal)
• Looping constructs: for (forLoop), while (WhileLoop), do-while (doWhile), and nested loops (nestedLoop)
• Methods: parameters, return values, and simple overloading (Methods)
• String operations: length, case conversion, indexing, concatenation, and escape sequences (Strings)
• User input using java.util.Scanner (Input)
• Recursion with a factorial-like example (Recursion)

Each class includes a main method and can be compiled and run independently. This makes it easy to experiment with one concept at a time.

Prerequisites

• Java Development Kit (JDK) 8+ installed
• A terminal/shell to run javac and java
• Optional: An IDE (IntelliJ IDEA, VS Code, Eclipse) for easier editing and running

You can verify Java is available with:

java -version
javac -version

Installation and Usage

This project has no build system (no Maven/Gradle). Use javac directly.

1. Navigate to the project root:

   cd /home/klemoh/Java

2. Compile all sources into an out directory:

   mkdir -p out && javac -d out src/*.java

3. Run any example class (pick one at a time):

   java -cp out Main
   java -cp out Conditonal
   java -cp out forLoop
   java -cp out WhileLoop
   java -cp out doWhile
   java -cp out nestedLoop
   java -cp out Methods
   java -cp out Strings
   java -cp out Input
   java -cp out Recursion

Notes:

• Classes like forLoop, doWhile, and nestedLoop intentionally use lowercase first letters to match the filenames; use the exact class names when running.
• Programs that read input (Input, Conditonal, doWhile) expect terminal input and will wait for your response.

Quick Reference Table

Class	Concept(s) Demonstrated	Entry Point
Main	Variables, primitives vs references, simple if/else, math	public static void main(String[])
Conditonal	Scanner input, ternary operator, chained ternaries	main
forLoop	for loop	main
WhileLoop	while loop, countdown	main
doWhile	do-while loop with input	main
nestedLoop	Nested loops, multiplication table cells	main
Methods	Methods, conditional logic inside a method, overloading	main
Strings	String API: length, case, index, concatenation, escapes	main
Input	Scanner input, reading String and int, simple arithmetic	main
Recursion	Recursive multiplication (factorial-like)	main

Code Walkthrough

Below are annotated snippets organized by topic. Each snippet is preceded by an explanation.

Variables, Types, and Basic I/O (Main)

Demonstrates primitive vs reference types, if/else, arithmetic, and string length.

public class Main {
    public static void main(String[] args) {
        int age = 30;
        char grade = 'A';
        String name = "Clement";
        boolean isStudent = true;

        if (isStudent) {
            System.out.println("You are a student");
        } else {
            System.out.println("you are not student");
        }

        int items = 50;
        float costPerItem = 9.99f;
        float totalCost = items * costPerItem;
        char currency = '$';
        String txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        System.out.println("The length of the txt string is: " + txt.length());

        System.out.println("Number of items: " + items);
        System.out.println("Cost per item: " + costPerItem + currency);
        System.out.println("Total cost = " + totalCost + currency);
        System.out.println(isStudent);

        System.out.println(age + " " + grade + " " + name);
    }
}

Key points:

• Primitives: int, char, boolean, float store values directly.
• Reference types: String references objects.
• String.length() returns the number of characters.

Ternary Operator and Input (Conditonal)

Reads an integer door code and uses ternary operations to determine output. Also shows a chained ternary for sign checking.

import java.util.Scanner;

public class Conditonal {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Please enter your code:\n");
        int doorCode = scanner.nextInt();

        System.out.println(doorCode == 1337 ? "you may Enter" : "You are not allowed to order");

        int myNum = 10;
        String result = (myNum > 0) ?
            "The value is Positive" :
            (myNum < 0) ?
            "The value is Negative" :
            "The value is 0";
        System.out.println(result);

        scanner.close();
    }
}

Loops

For loop (forLoop)

Counts from 0 to 4 using a for loop.

public class forLoop {
   public static void main(String[] args) {
       for (int i = 0; i < 5; i++) {
           System.out.println(i);
       }
   }
}

While loop (WhileLoop)

Counts down from 6 to 1, then prints a celebration message.

public class WhileLoop {
    public static void main(String args[]) {
        int countdown = 6;
        while (countdown > 0) {
            System.out.println(countdown);
            countdown--;
        }
        System.out.println("Happy new year");
    }
}

Do-while loop (doWhile)

Reads a starting integer and prints numbers up to 10 using a do-while loop.

import java.util.Scanner;
public class doWhile {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter an integer");
        int i = scanner.nextInt();
        do {
            System.out.println(i);
            i++;
        } while (i <= 10);
        scanner.close();
    }
}

Nested loops (nestedLoop)

Nested loops compute and print simple multiplication products.

public class nestedLoop {
    public static void main(String[] args) {
        for (int i = 1; i <= 3; i++) {
            for (int j = 1; j <= 3; j++) {
                System.out.println(i * j + " ");
            }
            System.out.println();
        }
    }
}

Methods and Overloading (Methods)

Demonstrates defining methods with parameters, conditional logic inside a method, and an overloaded method returning a value.

public class Methods {
    static void myMethod(String fname, int age) {
        System.out.println(fname + " is " + age);
        if (age < 18) {
            System.out.println("Access Denied");
        }
        if (age > 18) {
            System.out.println("Access Granted");
        }
    }

    static int myMethod(int X, int Y) {
        return Y + X;
    }

    public static void main(String[] args) {
        myMethod("Jenney", 5);
        myMethod("Anja", 31);
        int Z = myMethod(5, 3);
        System.out.print(Z);
    }
}

Parameters and return values:

Method signature	Parameters	Returns	Notes
void myMethod(String, int)	fname (name), age	void	Prints and gates by age
int myMethod(int X, int Y)	X, Y	int	Returns sum of two integers

String Operations (Strings)

Illustrates common string operations and escape sequences.

public class Strings {
    public static void main(String[] args) {
        String txt = "aqswdefrgthyjukilop";
        System.out.println("The length of the String is " + txt.length());
        System.out.println(txt.toUpperCase());
        System.out.println(txt.toLowerCase());
        System.out.println(txt.indexOf("t"));
        String firstName = "John";
        String lastName = "Doe";
        System.out.println(firstName + " " + lastName);
        System.out.println(firstName.concat(lastName));
        String txt2 = "It's alright.";
        String txt3 = "We \t are the \b so-called \"Vikings\" from \n the north.";
        System.out.println(txt2);
        System.out.println(txt3);
    }
}

Reading User Input (Input)

Prompts for a name and a number, then prints the square, cube, and fourth power of the number.

import java.util.Scanner;

public class Input {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter your Name:");
        String name = scanner.nextLine();
        System.out.println("Hello I am " + name);
        System.out.println("Enter a number:");
        int n = scanner.nextInt();
        System.out.println(n * n);           // square
        System.out.println(n * n * n);       // cube
        System.out.println(n * n * n * n);   // fourth power
        scanner.close();
    }
}

Recursion (Recursion)

Computes the product from k down to 1 recursively (i.e., k!).

public class Recursion {
    public static int sum(int k) {
        if (k > 1) {
            return k * sum(k - 1);
        } else {
            return 1;
        }
    }

    public static void main(String[] args) {
        int result = sum(10);
        System.out.println(result);
    }
}

Tips and Common Pitfalls

• Class names are case-sensitive when running with java. Use the exact class name.
• Close Scanner instances after use to release system resources.
• For simple projects like this, javac is sufficient. For larger projects, consider Maven or Gradle.

License

No license specified. Add one if you plan to share or reuse this code.