翻转单词顺序列,如“student. a am I”，返回的的句子应该是“I am a student.”。

import java.util.*;
public class Solution {
    public String ReverseSentence(String str) {
        if(str==null||str.length()==0){
            return "";
        }if(str.trim().equals("")){
            return str;
        }
        String[] strings = str.split(" ");
        List<String> list = new ArrayList<>();
        for(int i = strings.length - 1;i>=0;i--){
            list.add(strings[i]);
        }
        StringBuffer stringBuffer = new StringBuffer();
        for(int i =0;i<list.size();i++){
            if(i<list.size()-1){
                stringBuffer.append(list.get(i)+" ");
            }else{
                stringBuffer.append(list.get(i));
            }
            
        }
        return stringBuffer.toString();
    }
}