【Java每日一题】201612015

20161202问题解析请点击今日问题下方的“【Java每日一题】20161205”查看 

package Dec2016;    import java.util.HashSet;    public class Ques1205 {        public static void main(String[] args){            StringBuffer sb1 = new StringBuffer("123");          StringBuffer sb2 = new StringBuffer("123");          StringBuffer sb3 = new StringBuffer("123");          StringBuffer sb4 = new StringBuffer("123");            HashSet<StringBuffer> set = new HashSet<StringBuffer>();          set.add(sb1);          set.add(sb2);          set.add(sb3);          set.add(sb4);            System.out.println(set.size());      }  } 

今日问题： 
请问主程序输出结果是什么？（点击以下“【Java每日一题】20161205”查看20161202问题解析） 

题目原发布于公众号、简书：【Java每日一题】20161205，【Java每日一题】20161205