巧用^解决大小转换问题

• ^技巧

 String[] arr =  s.split(" ",-1);
        //数组元素入栈
        Stack<String> stack = new Stack<String>();
        for(String str:arr){
            stack.push(str);
        }
        //逆序出栈
        StringBuilder sb = new StringBuilder();
        while(!stack.isEmpty()){
            sb.append(stack.pop()+" ");
        }
        //去除最后一个空格
        sb.deleteCharAt(sb.length()-1);
        StringBuilder res = new StringBuilder();
        for(char c :sb.toString().toCharArray()){
            if(c==' '){
                res.append(c);
            }else {
                // 亦或技巧 字符a ^' ' 则大小写随意切换
                c^=' ';
                res.append(c);
            }
        }