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

There are various ways:

  • Through Class.newInstance.
  • Through Constructor.newInstance.
  • Through deserialisation (uses the no-args constructor of the most derived non-serialisable base class).
  • Through Object.clone (does not call a constructor).
  • Through JNI (should call a constructor).
  • Through any other method that calls a new for you.
  • I guess you could describe class loading as creating new objects (such as interned Strings).
  • A literal array as part of the initialisation in a declaration (no constructor for arrays).
  • The array in a "varargs" (...) method call (no constructor for arrays).
  • Non-compile time constant string concatenation (happens to produce at least four objects, on a typical implementation).
  • Causing an exception to be created and thrown by the runtime. For instance throw null; or "".toCharArray()[0].
  • Oh, and boxing of primitives (unless cached), of course.
  • JDK8 should have lambdas (essentially concise anonymous inner classes), which are implicitly converted to objects.
  • For completeness (and Paŭlo Ebermann), there's some syntax with the new keyword as well.

There are four different ways to create objects in java:

A. Using new keyword
This is the most common way to create an object in java. Almost 99% of objects are created in this way.

 MyObject object = new MyObject();

B. 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();

C. Using clone()
The clone() can be used to create a copy of an existing object.

MyObject anotherObject = new MyObject();
MyObject object = (MyObject) anotherObject.clone();

D. 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();

You can read them from here.

Tags:

Java