【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：[url=http://mp.weixin.qq.com/s?__biz=MzI4ODEyMTgwMA==&mid=2650163291&idx=1&sn=5f0b6b17b1d0999f09ef1420edc8c795&chksm=f3c1defcc4b657eaabc0883da471562417bf9da7af8435dbd25328f4d06105ea6d86c4c7a4f5#rd]【Java每日一题】20161205[/url]，[url=http://www.jianshu.com/p/9512b3483862]【Java每日一题】20161205[/url]

[img]https://img-blog.youkuaiyun.com/20161017115128961?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast[/img]