In how many ways we can create an object? could you Explain with example if possible.

[Madhava Thamatama]

In how many ways we can create an object? could you Explain with example if possible.

[Seetharaman Venkatasamy]

you can find many useful links, if you google

[fred rosenberger]

How many ways do you know, and what are they?

[Madhava Thamatama]

as my knowledge we can create object in 3 ways 1)by using new key word 2)class.foName() 3)clone() method .
could yu please tell me if you know any others ways to create object ?

[Rob Spoor]

De-serialization comes to mind.

[Matthew Brown]

Some more I can think of:

- Class.newInstance()
- Constructor.newInstance(Object...)
- Auto-boxing a primitive
- Use of String literal and array literals

[Wouter Oet]

Matthew Brown wrote:Some more I can think of:

- Class.newInstance()
- Constructor.newInstance(Object...)
- Auto-boxing a primitive
- Use of String literal and array literals

Auto-boxing will not necessarily create an object. It can in some cases just return an instance from a cache.

[Matthew Brown]

Wouter Oet wrote:Auto-boxing will not necessarily create an object. It can in some cases just return an instance from a cache.

Same with the String literals. But it can produce a new object.

[Wouter Oet]

True but autoboxing is nothing more than syntactic sugar. It's just a call to <Wrapper>.valueOf() and that may call a constructor. So it is debatable if auto-boxing creates it or if it's just a couple of linked calls to a constructor.

[Mike Simmons]

Yeah, both autoboxing and deserialization just end up calling constructors - one via the new keyword, and one via reflection. Not sure they really count as separate ways to create something. Then again, I'm not sure this distinction really matters - it depends why the person asking the question needs the information. Seems like a silly trivia question. Arguing the semantics doesn't seem that interesting.

[Rob Spoor]

Mike Simmons wrote:Yeah, both autoboxing and deserialization just end up calling constructors - one via the new keyword, and one via reflection.

De-serialization does not call any constructor. You can prove that easily:

import java.io.*;

class Test implements Serializable
{
    public Test()
    {
        System.out.println("Test constructor called");
    }

    public static void main(String[] args) throws Exception
    {
        Test test1 = new Test();
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);
        oos.writeObject(test1);
        oos.close();

        ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bais);
        Test test2 = (Test)ois.readObject();
        System.out.println(test1 == test2);
    }
}

Output:
Test constructor called
false

So the constructor is only called once, on line 12, and the two instances are not the same. That means that de-serialization created a new object without calling the constructor.

[Mike Simmons]

Hmmm, interesting - the situation for constructors in serialization is more complex than I realized. I overlooked that only the constructors of non-serializable superclasses are called during deserialization. So yes, there are cases where constructors aren't called in deserialization, even as there are cases where they are. But you're right, the former cases are sufficient for inclusion in this list.

[Jesper de Jong]

This question is a frequently asked question on the forums here. Every now and then somebody comes along that asks this exact same question. (Is this a standard question in interviews or at some school?).

If you do a search in the forums, you'll find older discussions and answers for this question.