Programming Tutorial: Java, Python, JavaScript

☕ Java — Input / Output

Basic input/output:

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String line = sc.nextLine();  // input one line
        String word = sc.next();  // input one word

        int num = sc.nextInt(); // input an integer number
        int dob = sc.nextDouble(); // input a double number

        System.out.println("Hello " + line + ", age = " + num);  // print and make new line
        System.out.print("Hello " + word + ", weight = " + dob);  // print without new line 

        System.out.printf("%.2f\n", value);  // print double with 2 decimal places
    }
}

Sum of 3 numbers (one line input):

import java.util.Scanner;

public class SumThree {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        System.out.println(a + b + c);
    }
}

Java — If Structure

int x = 10;

if (x > 0) {
    System.out.println("Positive");
} else if (x < 0) {
    System.out.println("Negative");
} else {
    System.out.println("Zero");
}

Java — Loops

for (int i = 1; i <= 5; i++)
    System.out.println(i);

int j = 1;
while (j <= 5) {
    System.out.println(j);
    j++;
}

Java — Arrays

int[] nums = {10, 20, 30};

for (int n : nums)
    System.out.println(n);

System.out.println(nums[1]); // 20

Java — Strings

String s = "Hello Java";

System.out.println(s.length());
System.out.println(s.toUpperCase());
System.out.println(s.substring(0, 5));
System.out.println(s.contains("Java"));

🐍 Python — Input / Output

Basic input/output:


text = input()  # input string 
num = int(input())  #input number

print(text)  # print and make a new line
print(num, end=' ')  # print and make a space

print(f"Hello {name}, age = {age}")

print(f"{num:.2f}") # print with 2 decimal places

Sum of 3 numbers (one line input):

a, b, c = map(int, input().split())
print(a + b + c)

Python — If Structure

x = 10

if x > 0:
    print("Positive")
elif x < 0:
    print("Negative")
else:
    print("Zero")

Python — Loops

for i in range(1, 6):
    print(i)

j = 1
while j <= 5:
    print(j)
    j += 1

Python — Lists (Arrays)

nums = [10, 20, 30]

# Input an array
nums = list(map(int, input().split()))

for n in nums:
    print(n)

print(nums[1])  # 20

Python — Strings

s = "Hello Python"

print(len(s))
print(s.upper())
print(s[0:5])
print("Python" in s)

✨ JavaScript — Input / Output (Custom Template)

Sum of 3 numbers from one line:

// Starter function main
function main() {
    // Read 3 numbers in one line
    let a = Number(input());
    let b = Number(input());
    let c = Number(input());

    println(a + b + c); // print and make a new line
    print(a.toFixed(2)); // print with 2 decimal places
}   

// --- Simplified input/output system ---
const fs = require("fs");

// Read all lines
let rawLines = fs.readFileSync(0, "utf8").split("\n").map(line => line.replace(/\r$/, ""));

let lineIndex = 0;
let tokenIndex = 0;
let currentTokens = [];

// Read next token
function input() {
    while (tokenIndex >= currentTokens.length) {
        if (lineIndex >= rawLines.length) return "";
        currentTokens = rawLines[lineIndex++].trim().split(/\s+/);
        tokenIndex = 0;
    }
    return currentTokens[tokenIndex++];
}

// Read rest of current line
function inputLine() {
    if (lineIndex >= rawLines.length && tokenIndex >= currentTokens.length) return "";
    if (tokenIndex < currentTokens.length) {
        let rest = currentTokens.slice(tokenIndex).join(" ");
        tokenIndex = currentTokens.length;
        return rest;
    }
    if (lineIndex < rawLines.length) {
        let line = rawLines[lineIndex++];
        currentTokens = line.trim().split(/\s+/);
        tokenIndex = currentTokens.length;
        return line;
    }
    return "";
}

function print(val) {
    process.stdout.write(String(val));
}

function println(val) {
    console.log(val);
}

main();

JavaScript — If Structure

let x = 10;

if (x > 0) {
    console.log("Positive");
} else if (x < 0) {
    console.log("Negative");
} else {
    console.log("Zero");
}

JavaScript — Loops

for (let i = 1; i <= 5; i++)
    console.log(i);

let j = 1;
while (j <= 5) {
    console.log(j);
    j++;
}

JavaScript — Arrays

let nums = [10, 20, 30];

    // Loop through array
    for (let n of nums) {
        console.log(n); // prints each element
    }

    // Access by index
    console.log(nums[1]); // 20

JavaScript — Strings

let s = "Hello JavaScript";

console.log(s.length);
console.log(s.toUpperCase());
console.log(s.substring(0, 5));
console.log(s.includes("Java"));