The following example implements the hexToDecimal(String hexString)  method, which converts a hex string into a decimal number.
 
import java.util.Scanner;
public class HexToDecimalConversion {
/** Main method */  

 public static void main(String[] args) {    

 Scanner input = new Scanner(System.in);
// Prompt the user to enter a string    

System.out.print("Enter a hex number: ");     

String hex = input.nextLine();    

  System.out.println("The decimal value for hex number " + hex + " is " + hexToDecimal(hex.toUpperCase()));  

 }
public static int hexToDecimal(String hex) {      

int decimalValue = 0;     for (int i = 0; i < hex.length(); i++) {

       char hexChar = hex.charAt(i);      

 decimalValue = decimalValue * 16 + hexCharToDecimal(hexChar);    

 }
return decimalValue; 

  }


public static int hexCharToDecimal(char ch) {    

  if (ch >= 'A' && ch <= 'F')      

 return 10 + ch - 'A';     

else

 // ch is '0', '1', ..., or '9'       

return ch - '0';     

} 

}

 
● Implement the hexToDecimal method to throw a  NumberFormatException if the string is not a hex string.