Ways to Create an Object of a Class

There are four ways to create objects in Java. Strictly speaking, there is only one way(by using a new keyword), and the rest internally use a new keyword. 

1. Using new keyword

It is the most common and general way to create an object in Java. 

Example:

// creating object of class Test
Test t = new Test();

2. Using Class.forName(String className) method

There is a pre-defined class in java.lang package with name Class. The forName(String className) method returns the Class object associated with the class with the given string name. We have to give a fully qualified name for a class. On calling the new Instance() method on this Class object returns a new instance of the class with the given string name.

// creating object of public class Test
// consider class Test present in com.p1 package
Test obj = (Test)Class.forName("com.p1.Test").newInstance();

3. Using clone() method

clone() method is present in the Object class. It creates and returns a copy of the object.

// creating object of class Test
Test t1 = new Test();
// creating clone of above object
Test t2 = (Test)t1.clone();

4. Deserialization

De-serialization is a technique of reading an object from the saved state in a file. Refer to Serialization/De-Serialization in Java

FileInputStream file = new FileInputStream(filename);
ObjectInputStream in = new ObjectInputStream(file);
Object obj = in.readObject();

Creating multiple objects by one type only (A good practice) 

In real-time, we need different objects of a class in different methods. Creating a number of references for storing them is not a good practice and therefore we declare a static reference variable and use it whenever required. In this case, the wastage of memory is less. The objects that are not referenced anymore will be destroyed by the Garbage Collector of Java. 

Example:

Test test = new Test();
test = new Test();

In the inheritance system, we use a parent class reference variable to store a sub-class object. In this case, we can switch into different subclass objects using the same referenced variable. 

Example:

class Animal {}
class Dog extends Animal {}
class Cat extends Animal {}
public class Test
{
    // using Dog object
    Animal obj = new Dog();
    // using Cat object
    obj = new Cat();
}

In Java, classes and objects are basic concepts of Object Oriented Programming (OOPs) that are used to represent real-world concepts and entities. The class represents a group of objects having similar properties and behavior. For example, the animal type Dog is a class while a particular dog named Tommy is an object of the Dog class.

In this article, we will discuss Java objects and classes and how to implement them in our program.