What are 5 Different Ways To Create Objects In Java? Explained With Example

While being a Java developer we usually create lots of objects daily, but we always use the new or dependency management systems e.g. Spring to create these objects. However, there are more ways to create objects which we are going to study in this article.

There are total 5 core ways to create objects in Java which are explained below with their example followed by bytecode of the line which is creating the object. However, lots of Apis are out there are which creates objects for us but these Apis will also are using one of these 5 core ways indirectly e.g. Spring BeanFactory.

5-different-ways-of-object-creation-in-Java-with-example-and-explanation

If you will execute program given in the 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 the new keyword

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

 Employee emp1 = new Employee();
 0: new           #19              // class org/programming/mitra/exercises/Employee
 3: dup
 4: invokespecial #21              // Method org/programming/mitra/exercises/Employee."":()V


2. Using Class.newInstance() method

We can also use the newInstance() method of the Class class to create objects, This newInstance() method calls the no-arg constructor to create the object.
We can create objects by newInstance() in the following way.

Employee emp2 = (Employee) Class.forName("org.programming.mitra.exercises.Employee")
                               .newInstance();

Or

Employee emp2 = Employee.class.newInstance();
51: invokevirtual    #70    // Method java/lang/Class.newInstance:()Ljava/lang/Object;


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 a 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 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. To know the differences between both newInstance() methods read Creating objects through Reflection in Java with Example.

Constructor<Employee> constructor = Employee.class.getConstructor();
Employee emp3 = constructor.newInstance();
111: invokevirtual  #80  // Method java/lang/reflect/Constructor.newInstance:([Ljava/lang/Object;)Ljava/lang/Object;

4. Using clone() method

Whenever we call clone() on any object JVM actually creates a new object for us and copy all content of the previous object into it. Creating an object using the clone method does not invoke any constructor.

To use the clone() method on an object we need to implements Cloneable and define clone() method in it.

Employee emp4 = (Employee) emp3.clone();
162: invokevirtual #87  // Method org/programming/mitra/exercises/Employee.clone ()Ljava/lang/Object;

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. I have covered cloning in details in a 3 article long  Java Cloning Series which includes articles like Java Cloning And Types Of Cloning (Shallow And Deep) In Details With ExampleJava Cloning - Copy Constructor Versus CloningJava Cloning - Even Copy Constructors Are Not Sufficient. Please go ahead and read them if you want to know more about cloning.

5. Using deserialization

Whenever we serialize and then deserialize an object JVM creates a separate object for us. In deserialization, JVM doesn’t use any constructor to create the object.
To deserialize an object we need to implement the Serializable interface in our class.

ObjectInputStream in = new ObjectInputStream(new FileInputStream("data.obj"));
Employee emp5 = (Employee) in.readObject();
261: invokevirtual  #118   // Method java/io/ObjectInputStream.readObject:()Ljava/lang/Object;

As we can see in above bytecodes all 4 methods call 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 the constructor).

I have discussed serialization and deserialization in more details in serialization series which includes articles like Everything You Need To Know About Java SerializationHow To Customize Serialization In Java By Using Externalizable InterfaceHow To Deep Clone An Object Using Java In Memory Serialization. Please go ahead and read them if you want to know more about serialization.

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 below Java program, we are going to create Employee objects in all 5 ways, you can also found the complete source code at Github.

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
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41 comments :

  1. Replies
    1. While Deserialization, JVM uses a constructor to create aa object.

      Please find two scenarios.

      1. In our code, Employee class implements Serializable and there is no parent class, so Object class is parent class.

      While Deserialization, JVM uses a Object class constructor to create an object.

      2. If we create a new parent class and extend it in Employee class.

      While Deserialization, JVM uses a Person class constructor to create an object.

      Please find code sample.

      class Person {
      Person() {
      System.out.println("Person Class");
      }
      }

      class Employee extends Person implements Cloneable, Serializable {}

      Output :
      Person Class
      Employee [name=Akash], hashcode : 63313419

      Delete
    2. I see it, I think this might be happening because of constructor chaining (all super class constructors are getting called according to hierarchy) which is actually part of object creation.

      But Employee class's constructor does not get called as you can see by the running the code with below classes

      class Person {
      Person() {
      System.out.println("Person Class");
      }
      }

      class Employee extends Person implements Cloneable, Serializable {
      Employee(){
      System.out.println("Employee Class");
      }
      }

      Delete
  2. how to create an object with a name given by the user in java

    ReplyDelete
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  4. I trying understand this phrase:
    "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."
    What author has means? Most interesting:
    "until that object is full filling mandatory conditions of Java cloning"
    About which mandatory we are talking about?
    I don't understand that phrase at all ((:
    "full filling mandatory conditions"

    ReplyDelete
    Replies
    1. Thanks! @Hoz for expressing your concerns, If you read the link mentioned under the section `Using clone() method`, you will find out in order to call clone on a object your class have to implement Cloneable interface, should define a clone method of its own which should handle CloneNotSupportedException and call the clone() method of the superclass. And even after this much effort you will handle deep cloning separately. Please read the mentioned links for more details.

      Delete
  5. Java is an essential things to develop android application. Thanks for showing the different ways to create objects in java.

    ReplyDelete
  6. Thank you a lot, this was a great helo

    Note that the class Employee could add a `cloneSerialized()` method that contains the Serialized cloning clode. We could clone an `Employee employee` by just using `employee_clone = employee.cloneSerialized()`

    ReplyDelete
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