Set.toString() 是如何实现的？

The toString()方法未被覆盖Set或其层次结构，那么元素是如何打印的呢？

import java.lang.Math;
import java.util.HashSet;
class Hello{

public String name= ""; 

Hello(String name){

    this.name = name;   

}


public static void main(String args[]){

 Hello h1 = new Hello("first");
 Hello h2 = new Hello("second");
 Hello h3 = new Hello("third");
 Hello h4 = new Hello("fourth");
 Hello h5 = new Hello("fourth");

 HashSet hs = new HashSet(); 
 hs.add(h1);
 hs.add(h2);
 hs.add(h3);
 hs.add(h4);
 hs.add(h5);

 //hs.add(h5);
 //hs.add(null);

    System.out.println("elements in hashset"+hs);
      //System.out.println("elements in hashset"+hs.contains());
     //System.out.println("elements in hashset"+hs.contains(new Hello("who")));
    } 

    public boolean equals(Object obj){
        System.out.println("In Equals");
        System.out.println(name+"=====equals======"+((Hello)obj).name);
        if(name.equals(((Hello)obj).name))
            return true;
        else
             return false;
    }

    public int hashCode(){
        System.out.println("----In Hashcode----"+name); 
        return name.hashCode();
    }
}

Output :----In Hashcode----first
----In Hashcode----second
----In Hashcode----third
----In Hashcode----fourth
----In Hashcode----fourth
In Equals
fourth=====equals======fourth
----In Hashcode----fourth
----In Hashcode----second
----In Hashcode----third
----In Hashcode----first
elements in hashset[Hello@b4616a1a, Hello@c9
]
  

另外，当我打印 hashset 时，会为每个元素调用 hashcode 方法？这是否意味着迭代器调用此方法？

Set是一个接口。
它不能重写方法。

您正在使用HashSet class，它继承了AbstractCollection.toString() http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/util/AbstractCollection.java#AbstractCollection.toString%28%29