十六进制到二进制和十进制转换器

仅接受90到FF的十六进制范围内的数字。

import java.util.Scanner;

public class Main {
    public static int hex2decimal(String s) {
        String digits = "0123456789ABCDEF";
        s = s.toUpperCase();
        int val = 0;
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            int d = digits.indexOf(c);
            val = 16 * val + d;
        }
        return val;
    }

    public static void main(String args[]) {
        String hexdecnum;
        int decnum, i = 1, j;

        int binnum[] = new int[100];
        Scanner scan = new Scanner(System.in);
        boolean valid;
        do {
            valid = true;
            System.out.print("Enter Hexadecimal number in the range of 90 to FF: ");
            hexdecnum = scan.nextLine();
            final int MAX_LENGTH = 2;

            if (hexdecnum.matches("[A-Fa-f0-9]{2}") && hex2decimal(hexdecnum) >= 144) {
                /* first convert the hexadecimal to decimal */

                decnum = hex2decimal(hexdecnum);
                System.out.print("Equivalent Dec Number is : " + decnum);
                System.out.println();

                /* now convert the decimal to binary */

                while (decnum != 0) {
                    binnum[i++] = decnum % 2;
                    decnum = decnum / 2;
                }

                System.out.print("Equivalent Binary Number is : ");
                for (j = i - 1; j > 0; j--) {
                    System.out.print(binnum[j]);
                }
            } else {
                System.out.println("ERROR: Invalid Input");
                valid = false;
            }
        } while (!valid);
    }
}

运行示例：

Enter Hexadecimal number in the range of 90 to FF: abc
ERROR: Invalid Input
Enter Hexadecimal number in the range of 90 to FF: ab
Equivalent Dec Number is : 171
Equivalent Binary Number is : 10101011

另一个示例运行：

Enter Hexadecimal number in the range of 90 to FF: AG
ERROR: Invalid Input
Enter Hexadecimal number in the range of 90 to FF: AB
Equivalent Dec Number is : 171
Equivalent Binary Number is : 10101011

另一个示例运行：

Enter Hexadecimal number in the range of 90 to FF: 21
ERROR: Invalid Input
Enter Hexadecimal number in the range of 90 to FF: 90
Equivalent Dec Number is : 144
Equivalent Binary Number is : 10010000

另一个示例运行：

Enter Hexadecimal number in the range of 90 to FF: 40
ERROR: Invalid Input
Enter Hexadecimal number in the range of 90 to FF: FF
Equivalent Dec Number is : 255
Equivalent Binary Number is : 11111111

回答来源：Stack Overflow