熟能生巧

public class Solution {
    public String ReverseSentence(String str) {
        if(str==null||str.trim().length()==0) return str;
        //空格分隔转字符串数组
        String[] arr = str.split(" ");
        StringBuilder sb = new StringBuilder();
        //数组逆向拼接字符串，中间加空格
        for(int i=0;i<arr.length;i++){
            sb.append(arr[arr.length-1-i]+" ");
        }
        //去除尾部空格转字符串输出
        return sb.deleteCharAt(sb.length()-1).toString();

    }
}