对这行代码进行逐句注释import java.util.Scanner; public class HexToDecUseException { public static void main(String [] args) { Scanner input = new Scanner(System.in); try { System.out.print("Enter a hex number: "); String hexString = input.next(); int decNumber = hexToDex(hexString); System.out.println("The decimal value for hex number " + hexString + " is " + decNumber); } catch (NumberFormatException ex) { System.out.println(ex.toString() + " not a hex string."); } } public static int hexToDex(String hexString) throws NumberFormatException { int result = 0; for (int i = hexString.length() - 1; i >= 0; i--) { int judge = judge(hexString.charAt(i)); if (judge == -1) { throw new NumberFormatException(hexString); } else result += judge * Math.pow(16, (hexString.length() - i - 1)); } return result; } public static int judge(char ch) { if (ch >= '0' && ch <= '9') { return (ch - '0'); } else if (ch >= 'A' && ch <= 'F') { return (ch - 'A' + 10); } else return -1; } }

代码注释如下：

import java.util.Scanner;

public class HexToDecUseException {
    // 定义程序入口
    public static void main(String [] args) {
        // 创建 Scanner 对象，用于获取用户输入
        Scanner input = new Scanner(System.in);
        try {
            // 提示用户输入十六进制数
            System.out.print("Enter a hex number: ");
            // 获取用户输入的字符串
            String hexString = input.next();
            // 调用 hexToDex 方法将十六进制数转换为十进制数
            int decNumber = hexToDex(hexString);
            // 输出转换后的结果
            System.out.println("The decimal value for hex number " + hexString +
                               " is " + decNumber);
        } catch (NumberFormatException ex) {
            // 如果输入的字符串不是合法的十六进制数，则输出错误信息
            System.out.println(ex.toString() + " not a hex string.");
        }
    }

    // 定义将十六进制数转换为十进制数的方法
    public static int hexToDex(String hexString) throws NumberFormatException {
        int result = 0;
        // 从字符串的末尾开始遍历
        for (int i = hexString.length() - 1; i >= 0; i--) {
            // 判断当前字符是否为合法的十六进制数
            int judge = judge(hexString.charAt(i));
            if (judge == -1) {
                // 如果不是合法的十六进制数，则抛出 NumberFormatException 异常
                throw new NumberFormatException(hexString);
            } else {
                // 将当前字符对应的十进制数加入到结果中
                result += judge * Math.pow(16, (hexString.length() - i - 1));
            }
        }
        // 返回转换后的十进制数
        return result;
    }

    // 定义判断十六进制数的方法，如果是合法的十六进制数返回对应的十进制数，否则返回 -1
    public static int judge(char ch) {
        if (ch >= '0' && ch <= '9') {
            return (ch - '0');
        } else if (ch >= 'A' && ch <= 'F') {
            return (ch - 'A' + 10);
        } else {
            return -1;
        }
    }
}