java中输入一字符，小写变大写，大写变小写，怎么编？？

public class UpperOrLower{ public static void main(String[] args){ //判断参数程序传入的参数是否为1 if(args.length != 1){ System.out.println("Error! Require on param. or more one param."); return; }else{ String result = toAllUppe