1、练习-转换罗马数字

键盘录入一个字符串

要求1：长度为小于等于9

要求2：只能是数字

将内容变成罗马数字

下面是阿拉伯数字跟罗马数字的对比关系：

Ⅰ-1

Ⅱ-2

Ⅲ-3

Ⅳ-4

Ⅴ-5

Ⅵ-6

Ⅶ-7

Ⅷ-8

Ⅸ-9

注意点：罗马数字里面没有0的，如果键盘录入的数字包含0，可以变成”“（长度为0的字符串）

2、第一种解题思想（查表法）

package stringdemo;import java.util.Scanner;public class Test {public static void main(String[] args) {Scanner sc = new Scanner(System.in);String str;while (true) {System.out.println("请输入一个字符串");str = sc.next();boolean flag = checkStr(str);if (flag) {break;} else {System.out.println("当前的字符串不符合规则，请重新输入");continue;}}StringBuilder sb = new StringBuilder();for (int i = 0; i < str.length(); i++) {char c = str.charAt(i);int number = c - 48;String s = changeLuoMa(number);sb.append(s);}System.out.println(sb);}/*Ⅰ-1   Ⅱ-2     Ⅲ-3     Ⅳ-4     Ⅴ-5     Ⅵ-6     Ⅶ-7     Ⅷ-8    Ⅸ-9
*/public static String changeLuoMa(int number) {String[] arr = {"", "Ⅰ", "Ⅱ", "Ⅲ", "Ⅳ", "Ⅴ", "Ⅵ", "Ⅶ", "Ⅷ", "Ⅸ"};return arr[number];}public static boolean checkStr(String string) {if (string.length() > 9) {return false;}for (int i = 0; i < string.length(); i++) {char c = string.charAt(i);if (c < '0' || c > '9') {return false;}}return true;}}
D:\Java\jdk-17\bin\java.exe "-javaagent:D:\BaiduNetdiskDownload\IntelliJ IDEA 2023.2\lib\idea_rt.jar=2084:D:\BaiduNetdiskDownload\IntelliJ IDEA 2023.2\bin" -Dfile.encoding=UTF-8 -classpath F:\IdeaProjects\JavaSenior\out\production\Exception stringdemo.Test
请输入一个字符串
123456789
ⅠⅡⅢⅣⅤⅥⅦⅧⅨProcess finished with exit code 0

3、第二种解题思想（switch）

package stringdemo;import java.util.Scanner;public class TestCase {public static void main(String[] args) {Scanner sc = new Scanner(System.in);String str;while (true) {System.out.println("请输入一个字符串");str = sc.next();boolean flag = checkStr(str);if (flag) {break;} else {System.out.println("当前的字符串不符合规则，请重新输入");continue;}}StringBuilder sb = new 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);}/*Ⅰ-1   Ⅱ-2     Ⅲ-3     Ⅳ-4     Ⅴ-5     Ⅵ-6     Ⅶ-7     Ⅷ-8    Ⅸ-9*/public static String changeLuoMa(char number) {String str = switch (number) {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;}public static boolean checkStr(String string) {if (string.length() > 9) {return false;}for (int i = 0; i < string.length(); i++) {char c = string.charAt(i);if (c < '0' || c > '9') {return false;}}return true;}
}
D:\Java\jdk-17\bin\java.exe "-javaagent:D:\BaiduNetdiskDownload\IntelliJ IDEA 2023.2\lib\idea_rt.jar=2435:D:\BaiduNetdiskDownload\IntelliJ IDEA 2023.2\bin" -Dfile.encoding=UTF-8 -classpath F:\IdeaProjects\JavaSenior\out\production\Exception stringdemo.TestCase
请输入一个字符串
123456789
ⅠⅡⅢⅣⅤⅥⅦⅧⅨProcess finished with exit code 0

4、调正字符串

给定两个字符串，A和B

A的旋转操作就是将A最左边的字符移动到最右边。

例如,若A='abcde',在移动一次之后结果就是'bcdea'。

如果在若干次调整操作之后，A能变成B，那么返回True。

如果不能匹配成功，则返回false

4.1、如果我们看到要修改字符串的内容，可以有两种方法：

1. 用subString进行截取，把左边的字符截取出来拼接到右侧去
2. 可以把字符串先变成一个字符数组，然后调整字符数组里面数据，最后再把字符数组变成字符串。

4.1.1、第一种思路（subString）

​package stringdemo;public class Case1 {public static void main(String[] args) {String strA = "abcde";String strB = "cdeab";boolean result = check(strA, strB);System.out.println(result);}public static boolean check(String strA, String strB) {for (int i = 0; i < strA.length(); i++) {strA = rotate(strA);if (strA.equals(strB)) {return true;}}return false;}public static String rotate(String str) {char first = str.charAt(0);String end = str.substring(1);return end + first;}
}
D:\Java\jdk-17\bin\java.exe "-javaagent:D:\BaiduNetdiskDownload\IntelliJ IDEA 2023.2\lib\idea_rt.jar=3417:D:\BaiduNetdiskDownload\IntelliJ IDEA 2023.2\bin" -Dfile.encoding=UTF-8 -classpath F:\IdeaProjects\JavaSenior\out\production\Exception stringdemo.Case1
trueProcess finished with exit code 0​

4.1.2、第二种思路

package stringdemo;public class Case2 {public static void main(String[] args) {String strA = "abcde";String strB = "cdeab";boolean result = check(strA, strB);System.out.println(result);}public static boolean check(String strA, String strB) {for (int i = 0; i < strA.length(); i++) {strA = rotate(strA);if (strA.equals(strB)) {return true;}}return false;}public static String rotate(String str) {char[] arr = str.toCharArray();char first = arr[0];for (int i = 1; i < arr.length; i++) {arr[i - 1] = arr[i];}arr[arr.length - 1] = first;String result = new String(arr);return result;}
}
D:\Java\jdk-17\bin\java.exe "-javaagent:D:\BaiduNetdiskDownload\IntelliJ IDEA 2023.2\lib\idea_rt.jar=3381:D:\BaiduNetdiskDownload\IntelliJ IDEA 2023.2\bin" -Dfile.encoding=UTF-8 -classpath F:\IdeaProjects\JavaSenior\out\production\Exception stringdemo.Case2
trueProcess finished with exit code 0