【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