What are all the different ways to create an object in Java?

Question

Had a conversation with a coworker the other day about this.

There's the obvious which is to use a constructor, but what other ways are there?

Answer 1

Cloning and deserialization.

Answer 2

Reflection:

someClass.newInstance();

Answer 3

With Reflexion too..

Answer 4

Reflection, but that ultimately uses a constructor.

Answer 5

Depends exactly what you mean by create but some other ones are:

• Clone method
• Deserialization
• Reflection (Class.newInstance())
• Reflection (Constructor object)

Answer 6

When in doubt, look at the language spec.

12.5 Creation of New Class Instances http://java.sun.com/docs/books/jls/third_edition/html/execution.html#12.5

15.9 Class Instance Creation Expressions http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#41147

Answer 7

Within the Java language, the only way to create an object is by calling it's constructor, be it explicitly or implicitly. Using reflection results in a call to the constructor method, deserialization uses reflection to call the constructor, factory methods wrap the call to the constructor to abstract the actual construction and cloning is similarly a wrapped constructor call.

Answer 8

You can also instantiate objects via JNI.

Answer 9

From an API user perspective, another alternative to constructors are static factory methods (like BigInteger.valueOf()), though for the API author (and technically "for real") the objects are still created using a constructor.

Answer 10

there is also ClassLoader.loadClass(string) but this is not often used.

and if you want to be a total lawyer about it, arrays are technically objects because of an array's .length property. so initializing an array creates an object.

Answer 11

From Josh block: used named static methods as "constructors" as they are more readable, as opposed to many constructors named the same with differing parameter lists.

--James

Answer 12

There are four different ways (I really don’t know is there a fifth way to do this) to create objects in java:

1. Using new keyword This is the most common way to create an object in java. I read somewhere that almost 99% of objects are created in this way.

MyObject object = new MyObject();2. Using Class.forName() If we know the name of the class & if it has a public default constructor we can create an object in this way.

MyObject object = (MyObject) Class.forName("subin.rnd.MyObject").newInstance(); 3. Using clone() The clone() can be used to create a copy of an existing object.

MyObject anotherObject = new MyObject(); MyObject object = anotherObject.clone();4. Using object deserialization Object deserialization is nothing but creating an object from its serialized form.

ObjectInputStream inStream = new ObjectInputStream(anInputStream ); MyObject object = (MyObject) inStream.readObject();Now you know how to create an object. But its advised to create objects only when it is necessary to do so.

Answer 13

There r Six Ways to Create an Object....... 1) new Class Constructor(); 2) Factory Methods 3) Cloning 4) Using Class methods 5) class.new Instance(); 6) deserilization