编写博客目的：本系列博客均根据B站黑马程序员系列视频学习和编写目的在于记录自己的学习点滴，方便后续回忆和查找相关知识点，不足之处恳请各位有缘的朋友指正。

 一、字符串拼接

 第一题：false

第二题：true 

二、 字符串转换

package StringJoinerDemo1;

import java.util.Scanner;

public class StringJoinerDemo2 {
    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("当前字符串不符合规则，请重新输入");
                continue;
            }
        }
        String s = "";
        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);
            int number = c - 48;
            s = s + changeLuoMa(number);
        }
        System.out.println(s);

    }

    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 str) {
        if (str.length() > 9) {
            return false;
        }

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

三、调整字符串内容并比较

package test;

public class test1 {
    public static void main(String[] args) {
        // 定义两个字符串
        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;
    }
}