java基础练习--字符串之罗马数字转换--两种转换方法

方法1：查表法

 //数字-->罗马字符
    public static String changeLuoMa(int number){
        String[] arr = {"","Ⅰ","Ⅱ","Ⅲ","Ⅳ","Ⅴ","Ⅵ","Ⅶ","Ⅷ","Ⅸ",};

        return arr[number];

    }

完整代码：

import java.util.Scanner;

public class Test1Case1 {
    public static void main(String[] args) {

        //键盘录入字符串
        Scanner sc = new Scanner(System.in);
        String str;
        //条件判断
        while (true) {
            str = sc.next();
            boolean flag = checkStr(str);
            if (flag){
                break;
            }else {
                System.out.println("当前字符串不符合规则，请重新输入");
                continue;
            }
        }

        StringBuilder sb = new StringBuilder();//罗马字符拼接用StringBuilder
        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);
            int number = c - 48;//数字字符-->数字
            String s = changeLuoMa(number);
            sb.append(s);
        }

        System.out.println(sb);
    }
    //数字-->罗马字符
    public static String changeLuoMa(int number) {
        String[] arr = {"", "Ⅰ", "Ⅱ", "Ⅲ", "Ⅳ", "Ⅴ", "Ⅵ", "Ⅶ", "Ⅷ", "Ⅸ",};
        return arr[number];
    }

    //判断录入的字符串是否满足条件：
    //1.字符串<=9
    //2.字符串只能是数字
    public static boolean checkStr(String str){

        if (str.length()>9){
            return false;
        }
        for (int i = 0; i < str.length(); i++) {//遍历字符串
            char c = str.charAt(i);
            if (c<'0'||c>'9'){
                return false;
            }
        }
        return true;
    }
}

方法2：switch语句

 //数字-->罗马字符
    public static String changeLuoMa(char c){

        String str = switch (c){
            case '0'->"";
            case '1'->"Ⅰ";
            case '2'->"Ⅱ";
            case '3'->"Ⅲ";
            case '4'->"Ⅳ";
            case '5'->"Ⅴ";
            case '6'->"Ⅵ";
            case '7'->"Ⅶ";
            case '8'->"Ⅷ";
            case '9'->"Ⅸ";
            default->str = "";
        };
        return str;
    }

完整代码：

import java.util.Scanner;

public class Test1Case2 {
    public static void main(String[] args) {

        //键盘录入字符串
        Scanner sc = new Scanner(System.in);
        String str;
        //条件判断
        while (true) {
            str = sc.next();
            boolean flag = checkStr(str);
            if (flag){
                break;
            }else {
                System.out.println("当前字符串不符合规则，请重新输入");
                continue;
            }
        }

       StringBuilder sb = new StringBuilder();//罗马字符拼接用StringBuilder
        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);

            String s = changeLuoMa(c);
            sb.append(s);
        }

        System.out.println(sb);
    }
    //数字-->罗马字符
    public static String changeLuoMa(char c){

        String str = switch (c){
            case '0'->"";
            case '1'->"Ⅰ";
            case '2'->"Ⅱ";
            case '3'->"Ⅲ";
            case '4'->"Ⅳ";
            case '5'->"Ⅴ";
            case '6'->"Ⅵ";
            case '7'->"Ⅶ";
            case '8'->"Ⅷ";
            case '9'->"Ⅸ";
            default->str = "";
        };
        return str;
    }

    //判断录入的字符串是否满足条件：
    //1.字符串<=9
    //2.字符串只能是数字
    public static boolean checkStr(String str){

        if (str.length()>9){
            return false;
        }
        for (int i = 0; i < str.length(); i++) {//遍历字符串
            char c = str.charAt(i);
            if (c<'0'||c>'9'){
                return false;
            }
        }
        return true;
    }
}