Example: Binary-Decimal Converter with User Input in Java

// Binary-Decimal Converter with User Input
import java.util.Scanner;

// Main class containing the entry point of the program
public class Main {

    /**
     * Converts a binary string to its decimal equivalent.
     * @param binaryString The binary number as a string.
     * @return The decimal equivalent of the binary string.
     */
    public static int binaryToDecimal(String binaryString) {
        int decimal = 0;
        int power = 0;
        for (int i = binaryString.length() - 1; i >= 0; i--) {
            char bit = binaryString.charAt(i);
            if (bit == '1') {
                decimal += Math.pow(2, power);
            } else if (bit != '0') {
                // Handle invalid binary input
                throw new IllegalArgumentException("Invalid binary string: " + binaryString);
            }
            power++;
        }
        return decimal;
    }

    /**
     * Converts a decimal integer to its binary string equivalent.
     * @param decimal The decimal number.
     * @return The binary string representation of the decimal number.
     */
    public static String decimalToBinary(int decimal) {
        if (decimal == 0) {
            return "0";
        }
        if (decimal < 0) {
            // For simplicity, handle only positive integers. For negative, Two's Complement is needed.
            throw new IllegalArgumentException("Negative numbers not supported for simple binary conversion.");
        }

        StringBuilder binaryBuilder = new StringBuilder();
        int tempDecimal = decimal;
        while (tempDecimal > 0) {
            int remainder = tempDecimal % 2;
            binaryBuilder.append(remainder);
            tempDecimal /= 2;
        }
        return binaryBuilder.reverse().toString();
    }

    public static void main(String[] args) {
        // Step 1: Create a Scanner object to read user input
        Scanner scanner = new Scanner(System.in);

        // Step 2: Prompt the user for the type of conversion
        System.out.println("Choose conversion type:");
        System.out.println("1. Binary to Decimal");
        System.out.println("2. Decimal to Binary");
        System.out.print("Enter your choice (1 or 2): ");
        int choice = scanner.nextInt();

        // Step 3: Perform conversion based on user's choice
        try {
            if (choice == 1) {
                System.out.print("Enter a binary number: ");
                String binaryInput = scanner.next();
                int decimalResult = binaryToDecimal(binaryInput);
                System.out.println("Decimal equivalent: " + decimalResult);
            } else if (choice == 2) {
                System.out.print("Enter a decimal number: ");
                int decimalInput = scanner.nextInt();
                String binaryResult = decimalToBinary(decimalInput);
                System.out.println("Binary equivalent: " + binaryResult);
            } else {
                System.out.println("Invalid choice. Please enter 1 or 2.");
            }
        } catch (IllegalArgumentException e) {
            System.err.println("Error: " + e.getMessage());
        } finally {
            // Step 4: Close the scanner to prevent resource leaks
            scanner.close();
        }
    }
}