概述

String Joiner跟String Builder一样，亦可以看成是一个容器，创建之后iu里面的内容是可变的

作用

提高字符串的操作效率，而且代码编写特别简洁，但是目前市场上很少有人用

JDK8

 

 

package stringdemo;

import java.util.StringJoiner;

public class StringJoinerDemo2 {
    public static void main(String[] args) {
        //1.创建对象
        StringJoiner sj = new StringJoiner(",", "[", "]");
        //2.添加元素
        sj.add("aaa").add("bbb").add("ccc");
        int len = sj.length();
        System.out.println(len);//13 如果空格后面加空格，那么就是15
        System.out.println(sj);
        String str = sj.toString();
        System.out.println(str);

    }
}

 

小总结

 

package text6;

import java.util.Scanner;
import java.util.StringJoiner;

public class Luoma {
    public static void main(String[] args) {
        //键盘录入一个一个字符串
        Scanner sc = new Scanner(System.in);
        String str;
        while (true) {
            System.out.println("请输入一个字符串");
            str = sc.next();
            System.out.println(str);
            //2.校验字符串是否满足规则
            boolean flag = checkSter(str);
            if (flag){
                break;
            }else{
                System.out.println("输入的字符串里面只能是数字，请重新输入");
                continue;
            }
        }
        //将内容变成罗马数字
        //查表法
        StringJoiner sj = new StringJoiner("-");
        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);
            int number = c - 48;
            String s = changLuoMa(number);
            sj.add(s);
            sj.toString();
        }
        System.out.println(sj);
    }
    public  static String changLuoMa(int number){
        String[] arr = {"","Ⅰ","Ⅱ","Ⅲ","Ⅳ","Ⅴ","Ⅵ","Ⅶ","Ⅷ","Ⅸ"};
        return arr[number];
    }
    public static boolean checkSter(String str){
        //1.长度小于等于九
        if (str.length()>9){
            return false;
        }
        //2.只能是数字
        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);
            if (c < '0' || c > '9'){
                return false;
            }
        }
        return true;
    }
}