如何实现Set.toString（）？ [英] How is Set.toString() implemented?

问题描述

toString（）方法未在 Set 或其层次结构中重写，那么元素是如何打印的？

The toString() method is not overridden in Set or its hierarchy, so how are the elements printed?

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方法吗？这是否意味着迭代器调用了这个方法？

Also When I print hashset the hashcode method is called for each of the elements ?Does it mean the iterator calls this method ?

推荐答案

Set 是一个接口。

它无法覆盖方法。

Set is an interface.
It cannot override methods.

您正在使用 HashSet 类，它继承了 AbstractCollection.toString（）

You're using the HashSet class, which inherits AbstractCollection.toString()

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