如何实现Set.toString()？

Question

该toString()方法未被覆盖Set或其层次结构,因此如何打印元素？

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,为每个元素调用hashcode方法？这是否意味着迭代器调用此方法？

Answer 1

Set是一个界面.
它无法覆盖方法.

你正在使用继承的HashSet 类AbstractCollection.toString()

Answer 2

Set实现从AbstractCollection继承toString .Set元素输出为以逗号分隔的字符串列表.