How to convert Hexadecimal number to Decimal number in Java?

Problem Description :

Write a program in Java that converts Hexadecimal number to Decimal number.

Hexadecimal to Decimal conversion

Concept :

Click here to learn how to convert hexadecimal number to decimal number Mathematically.

Recommended :

Learn different methods of reversing a String, using.

• Library method of StringBuilder class.
• Iteration
• Recursion

Java Program :

	package com.javamultiplex.baseconversion;
	import java.util.Scanner;
	/**
	*
	* @author Rohit Agarwal
	* @category Base Conversion
	* @problem Convert Hexadecimal to Decimal
	*
	*/
	public class HexadecimalToDecimal {
	public static void main(String[] args) {
	Scanner input = null;
	try {
	input = new Scanner(System.in);
	System.out.println("Enter hexadecimal number : ");
	String number = input.next();
	if (isHexadecimalNumber(number)) {
	int decimal = getDecimalNumber(number);
	System.out.println("Decimal Number : " + decimal);
	} else {
	System.out.println("Please enter valid hexadecimal number.");
	}
	} finally {
	if (input != null) {
	input.close();
	}
	}
	}
	private static int getDecimalNumber(String number) {
	// Converting String to StringBuilder.
	StringBuilder string = new StringBuilder(number);
	string = string.reverse();
	int length = string.length();
	int digit, power, sum = 0;
	for (int i = 0; i < length; i++) {
	if (Character.isDigit(string.charAt(i))) {
	digit = string.charAt(i) - 48;
	} else {
	digit = getHexadecimalCharacterDigit(string.charAt(i));
	}
	power = (int) Math.pow(16, i);
	sum = sum + digit * power;
	}
	return sum;
	}
	private static int getHexadecimalCharacterDigit(char ch) {
	int digit = 0;
	switch (ch) {
	case 'A':
	case 'a':
	digit = 10;
	break;
	case 'B':
	case 'b':
	digit = 11;
	break;
	case 'C':
	case 'c':
	digit = 12;
	break;
	case 'D':
	case 'd':
	digit = 13;
	break;
	case 'E':
	case 'e':
	digit = 14;
	break;
	case 'F':
	case 'f':
	digit = 15;
	break;
	}
	return digit;
	}
	private static boolean isHexadecimalNumber(String number) {
	/*
	* Regular expression that matches string containing only digits [0-9]
	* and alphabets [A-F] or [a-f]
	*/
	String pattern = "^[0-9a-fA-F]+$";
	boolean result = false;
	if (number.matches(pattern)) {
	result = true;
	}
	return result;
	}
	}

view raw HexadecimalToDecimal.java hosted with ❤ by GitHub

Output :

Output - How to convert Hexadecimal number to Decimal number in Java?

References :

https://en.wikipedia.org/wiki/Regular_expression

http://docs.oracle.com/javase/7/docs/api/java/lang/String.html

https://docs.oracle.com/javase/7/docs/api/java/lang/StringBuilder.html

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Tags : Conversion problems, Hexadecimal to Decimal, Solution in Java, String, StringBuilder, Regular expressions, switch statement, if else statement, for loop, while loop.

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