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Five Different Ways to Create Objects in Java

Five Different Ways to Create Objects in Java

A list of five ways to create objects in Java, how they interact with constructors, and an example of how to utilize all of these methods.

👁 Naresh Joshi user avatar

Naresh Joshi

Updated Sep. 09, 20 · Opinion

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While being a Java developer, we usually create lots of objects daily, but we always use 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 five core ways to create objects in Java, which are explained below with their example, followed by the bytecode of the line creating the object. However, lots of Apis are out there which create objects for us, but these APIs will also are using one of these five core ways indirectly, e.g., Spring BeanFactory.

If you execute the program given in the end, you will see that method 1, 2, and 3 uses the constructor to create the object, while 4 and 5 don’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. Using this method, we can call whichever constructor we want to call (no-arg constructor and parameterized).

Java

Employee emp1 = new Employee();

Java

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

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:

Java

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

Java

Employee emp2 = Employee.class.newInstance();

Java

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 the parameterized constructor and private constructor by using this newInstance() method.

Java

Constructor<Employee> constructor = Employee.class.getConstructor();
Employee emp3 = constructor.newInstance();

Java

111: invokevirtual  #80  // Method java/lang/reflect/Constructor.newInstance:([Ljava/lang/Object;)Ljava/lang/Object;

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

4. Using `clone()` Method

Whenever we call clone() on any object, JVM 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 the clone() method on an object, we need to implement Cloneable and define the clone() method in it.

Java

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

Java

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

Java cloning is the most debatable topic in the Java community, and it 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 detail in a 3 article long, Java Cloning Series. 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.

Java

ObjectInputStream in = new ObjectInputStream(new FileInputStream("data.obj"));
Employee emp5 = (Employee) in.readObject();

Java

261: invokevirtual  #118   // Method java/io/ObjectInputStream.readObject:()Ljava/lang/Object;

As we can see in the above bytecodes, all four methods' calls get converted to invoke virtual (object creation is directly handled by these methods) except the first one, which got converted to two calls. One is new, and the other is invoke special (call to the constructor).

Example

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

Java

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 boolean equals(Object o) {
 if (this == o) return true;
 if (o == null || getClass() != o.getClass()) return false;
 Employee employee = (Employee) o;
 return Objects.equals(name, employee.name);
 }

 @Override
 public int hashCode() { return Objects.hash(name); }

 @Override
 public String toString() { return String.format("Employee{name='%s'}", 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 five ways.

Java

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

 // 1. Using new keyword
 Employee emp1 = new Employee();
 emp1.setName("emp1");


 // 2. Using Class class's newInstance() method
 Employee emp2 = Employee.class.newInstance();
 emp2.setName("emp2");


 // 3. Using Constructor class's newInstance() method
 Constructor<Employee> constructor = Employee.class.getConstructor();
 Employee emp3 = constructor.newInstance();
 emp3.setName("emp3");

 // 4. Using clone() method
 Employee emp4 = (Employee) emp3.clone();
 emp4.setName("emp4");


 // Serialization
 try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("data.obj"))) {
 out.writeObject(emp4);
 }

 // 5. Using Deserialization
 Employee emp5;
 try (ObjectInputStream in = new ObjectInputStream(new FileInputStream("data.obj"))) {
 emp5 = (Employee) in.readObject();
 emp5.setName("emp5");
 }

 System.out.println(emp1 + ", hashcode : " + emp1.hashCode());
 System.out.println(emp2 + ", hashcode : " + emp2.hashCode());
 System.out.println(emp3 + ", hashcode : " + emp3.hashCode());
 System.out.println(emp4 + ", hashcode : " + emp4.hashCode());
 System.out.println(emp5 + ", hashcode : " + emp5.hashCode());
 }
}

This program will give the following output:

Java

Employee Constructor Called...
Employee Constructor Called...
Employee Constructor Called...
Employee{name='emp1'}, hashcode : 3117192
Employee{name='emp2'}, hashcode : 3117193
Employee{name='emp3'}, hashcode : 3117194
Employee{name='emp4'}, hashcode : 3117195
Employee{name='emp5'}, hashcode : 3117196

You can find the complete source code for this article on this Github Repository, and please feel free to provide your valuable feedback.

Object (computer science) Java (programming language) Spring Framework Java virtual machine Clone (Java method) Spring Data

Published at DZone with permission of Naresh Joshi. See the original article here.

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