Technical Tip #21 - Technical Tip of the day....

T21: Knowledge Tip Of The Day....

Different ways to create objects in Java

There are many different ways to create objects in Java.

1) Using new Keyword : Using new keyword is the most basic way to create an object. This is the most common way to create an object in java.
example::
Demo obj = new Demo();

2) Using New Instance : If we know the name of the class & if it has a public default constructor we can create an object –Class.forName. We can use it to create the Object of a Class. Class.forName actually loads the Class in Java but doesn’t create any Object.
example::
Class cls = Class.forName("Demo");
Demo obj =
(Demo) cls.newInstance();

3) Using clone() method: Whenever clone() is called on any object, the JVM actually creates a new object and copies all content of the previous object into it. Creating an object using the clone method does not invoke any constructor.
To use clone() method on an object we need to implement Cloneable and define the clone() method in it.
example::
Demo obj1=new Demo();
Demo obj2 = (Demo) obj1.clone();
Here we are creating the clone of an existing Object and not any new Object.

4) Using newInstance() method of Constructor class : This is similar to the newInstance() method of a class. There is one newInstance() method in the java.lang.reflect.Constructor class which we can use to create objects. It can also call parameterized constructor, and private constructor by using this newInstance() method.

Both newInstance() methods are known as reflective ways to create objects. In fact newInstance() method of Class internally uses newInstance() method of Constructor class.
example::
Constructor<ReflectionExample> constructor
= ReflectionExample.class.getDeclaredConstructor();
ReflectionExample r = constructor.newInstance();

5) Using deserialization : Whenever we serialize and then deserialize an object, JVM creates a separate object. In deserialization, JVM doesn’t use any constructor to create the object.
To deserialize an object we need to implement the Serializable interface in the class.
example::
Serializing an Object :
DeserializationExample d =
new DeserializationExample("Demo");

Deserialization of Object :
DeserializationExample d;
ObjectOutputStream oos = new ObjectOutputStream(f);
d = (DeserializationExample)oos.readObject