5 Different Ways to Create Objects in Java

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There are five total ways to create objects in Java, which are explained below with their examples followed by bytecode of the line which is creating the object.

Using new keyword	} → constructor gets called
Using newInstance() method of Class class	} → constructor gets called
Using newInstance() method of Constructor class	} → constructor gets called
Using clone() method	} → no constructor call
Using deserialization	} → no constructor call

If you will execute program given in end, you will see method 1, 2, 3 uses the constructor to create the object while 4, 5 doesn’t call the constructor to create the object. 

1. Using new keywords

It is the most common and regular way to create an object and a very simple one also. By using this method we can call whichever constructor we want to call (no-arg constructor as well as parameterized).

Employee emp1 = new Employee();

2. Using newInstance() method of Class class 

We can also use the newInstance() method of a Class class to create an object. This newInstance() method calls the no-arg constructor to create the object.

We can create an object by newInstance() in the following way:

Employee emp2 = (Employee) Class.forName("com.Employee")

.newInstance();

3. Using newInstance() method of Constructor class 

Similar to the newInstance() method of Class class, There is one newInstance() method in the java.lang.reflect.Constructor class which we can use to create objects. We can also call parameterized constructor, and private constructor by using this newInstance() method.

Constructor<Employee> constructor = Employee.class.getConstructor();

Employee emp3 = constructor.newInstance();

Both newInstance() methods are known as reflective ways to create objects. In fact newInstance() method of Class class internally uses newInstance() method of Constructor class. That's why the later one is preferred and also used by different frameworks like Spring, Hibernate, Struts etc.

4. Using clone() method: 

Whenever we call clone() on any object, the JVM actually creates a new object for us 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.

Employee emp4 = (Employee) emp3.clone();

Java cloning is the most debatable topic in Java community and it surely does have its drawbacks but it is still the most popular and easy way of creating a copy of any object until that object is full filling mandatory conditions of Java cloning.

5. Using deserialization: 

Whenever we serialize and deserialize an object, the JVM creates a separate object for us. In deserialization, the JVM doesn’t use any constructor to create the object. 

To deserialize an object we need to implement a Serializable interface in our class. 

ObjectInputStream in = new ObjectInputStream

(new FileInputStream("data.obj"));

Employee emp5 = (Employee) in.readObject();

As we can see in the above bytecode snippets, all 4 methods are called and get converted to invokevirtual (object creation is directly handled by these methods) except the first one, which got converted to two calls: one is new and other is invokespecial (call to constructor).

Example

Let’s consider an Employee class for which we are going to create the objects:

class Employee implements Cloneable, Serializable {

    private static final long serialVersionUID = 1L;

    private String name;

    public Employee() {

        System.out.println("Employee Constructor Called...");

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    @Override

    public int hashCode() {

        final int prime = 31;

        int result = 1;

        result = prime * result + ((name == null) ? 0 : name.hashCode());

        return result;

    }

    @Override

    public boolean equals(Object obj) {

        if (this == obj)

            return true;

        if (obj == null)

            return false;

        if (getClass() != obj.getClass())

            return false;

        Employee other = (Employee) obj;

        if (name == null) {

            if (other.name != null)

                return false;

        } else if (!name.equals(other.name))

            return false;

        return true;

    }

    @Override

    public String toString() {

        return "Employee [name=" + name + "]";

    }

    @Override

    public Object clone() {

        Object obj = null;

        try {

            obj = super.clone();

        } catch (CloneNotSupportedException e) {

            e.printStackTrace();

        }

        return obj;

    }

}

In the below Java program we are going to create Employee objects in all 5 ways.

public class ObjectCreation {

    public static void main(String... args) throws Exception {

        // By using new keyword

        Employee emp1 = new Employee();

        emp1.setName("Naresh");

        System.out.println(emp1 + ", hashcode : " + emp1.hashCode());

        // By using Class class's newInstance() method

        Employee emp2 = (Employee) 

Class.forName("org.programming.mitra.exercises.Employee")

                               .newInstance();

        // Or we can simply do this

        // Employee emp2 = Employee.class.newInstance();

        emp2.setName("Rishi");

        System.out.println(emp2 + ", hashcode : " + emp2.hashCode());

        // By using Constructor class's newInstance() method

        Constructor<Employee> constructor = 

Employee.class.getConstructor();

        Employee emp3 = constructor.newInstance();

        emp3.setName("Yogesh");

        System.out.println(emp3 + ", hashcode : " + emp3.hashCode());

        // By using clone() method

        Employee emp4 = (Employee) emp3.clone();

        emp4.setName("Atul");

        System.out.println(emp4 + ", hashcode : " + emp4.hashCode());

        // By using Deserialization

        // Serialization

        ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("data.obj"));

        out.writeObject(emp4);

        out.close();

        //Deserialization

        ObjectInputStream in = new ObjectInputStream(new FileInputStream("data.obj"));

        Employee emp5 = (Employee) in.readObject();

        in.close();

        emp5.setName("Akash");

        System.out.println(emp5 + ", hashcode : " + emp5.hashCode());

    }

}

This program will give the following output:

Employee Constructor Called...

Employee [name=Naresh], hashcode : -1968815046

Employee Constructor Called...

Employee [name=Rishi], hashcode : 78970652

Employee Constructor Called...

Employee [name=Yogesh], hashcode : -1641292792

Employee [name=Atul], hashcode : 2051657

Employee [name=Akash], hashcode : 63313419