CODEWITHSUNDEEP
javanetwork-programminginetaddress
Jigar Subhash Rajput
Jigar Subhash Rajput

Reputation: 11

Is InetAddress a static class? why do we not use new key word with it?

Why we have not used newkeyword in the following program?

import java.net.InetAddress;
public class InetDemo{
    public static void main(String[] args){
        try{
            InetAddress ip=InetAddress.getByName("www.pinterest.com");

            System.out.println("Host Name: "+ip.getHostName());
            System.out.println("IP Address: "+ip.getHostAddress());
        }catch(Exception e){System.out.println(e);}
    }
}

Upvotes: 0

Views: 218

Answers (2)

Stephen C
Stephen C

Reputation: 719436

Is InetAddress a static class?

Well, in a sense yes. All top-level classes are implicitly static ... in the sense that they don't require an instance of an outer class.

But you are not asking the right question. Static classes and static methods are different concepts ...

Why do we not use new key word with it?

Now ... the right question.

Because InetAddress.getByName(...) is a static method call that creates and returns an instance of Inet4Address or Inet6Address which are subtypes of InetAddress.

Why did they do it this way? Why not just new it?

InetAddress objects are typically created by calling getByName or a related method on a String representing hostname or an array of bytes. This will give you either IPv4 or IPv6 addresses, or a mixture of both (with the getAll methods). Since the true type of the result depends on the actual runtime arguments, it is not possible to do this with a constructor and new.

There is another reason as well. In fact there is some caching going on under the covers. If the argument to (say) getByName is a DNS name string, avoiding expensive DNS lookups is a good performance optimization. So results of lookups are cached, and a getByName call can return an Inet4Address or Inet6Address that was created previously. You can't do that with a constructor and new.

As @Turing85 notes, this is an example of the factory method design pattern.

Upvotes: 1

Turing85
Turing85

Reputation: 20195

Looking at documentation of InetAddress, we see that this class does not provide public acessible constructors. It uses the factory method pattern instead.

Upvotes: 0

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