【Java每日一题】20161205

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