字母大小写转化

package test;

import java.util.Scanner;

public class change_letter {
    public static String Upper(String str){
        String result = "";
        for(int i = 0 ; i < str.length(); i++){
            int begin = (int)str.charAt(i) - 32;
            if(begin>=65 && begin<=90){
            char end = (char)begin;
            result = result + end;
        }
        else {

                char end = (char)(begin+32);
                result = result + end;
            }
        }
        return result;
    }

    public static String Lower(String str){
        String result = "";
        for(int i = 0 ; i < str.length(); i++) {
            int begin = (int) str.charAt(i) + 32;
            if (begin >= 97 && begin <= 122) {
                char end = (char) begin;
                result = result + end;
            }
            else{
                char end = (char) (begin-32);
                result = result + end;
            }
        }
        return result;
    }
    public static void main(String[] args) {
        System.out.print("请输入字符串 ： ");
        Scanner sr = new Scanner(System.in);
        String str = sr.next();
        System.out.println("输入的字符串为："+str);
        System.out.println("字符串全变为大写为 ："+ Upper(str));
        System.out.println("字符串全变为小写为 ："+Lower(str));
    }
}