Constructor in Java

Level : Intermediate
Mentor: Shailendra Chauhan
Duration : 00:04:00

What is Constructor in Java?

A constructor is a block of code that functions similarly to a method and is called when a class instance is created to allocate memory for the object. When you use the 'new' keyword to instantiate an object, at least one constructor is called each time, which helps with memory allocation.

Working of Constructor

When a class object is formed, its constructor is invoked, which initializes the class attributes.

Types of Constructors

There are 2 types of constructors in Java:

  1. Default Constructor
  2. Parameterized Constructor

Default Constructor in Java

In Java, default constructors are used to initialize class fields and objects and are declared without arguments to allow the compiler to create them automatically when the class is instantiated. They ease providing default values like 0 or null, and they also allow for customized initialization code, helping in object setup for specific user or program requirements.

Parameterized constructor in Java

Parameterized constructors in Java increase object-building flexibility by accepting arguments for initializing the object's state. They support overloading, enabling several versions with various parameter lists for diverse use cases, and assisting in complex object initialization and subclass instantiation.

Why Parameterized Constructors are used?

  • Customization: Parameterized constructors allow for object initialization customization.
  • Code Reusability: They allow you to reuse constructor functionality for various initial states.
  • Encapsulation: Parameterized constructors protect data integrity by enclosing initialization.
  • Constructor Overloading: This allows you to define numerous constructors with various parameter lists.
  • Clearer Object Creation: Improves code readability during object initialization.

Private Constructor in Java

A private constructor in Java limits access to the class that defines it, giving developers precise control over object instantiation. This ensures that objects are produced in a set order, reduces duplicate object creation, and reduces problems and errors, making it an essential tool for code control and object instantiation management in Java development.

Constructor Overloading in Java

Constructor overloading is the usage of many constructors in an instance class. Overloaded constructors must have separate signatures. For the compilation to be successful, each constructor must have a unique set of parameters.

Benefits of Constructor Overloading in Java

  • Flexibility: Using many constructors with varied parameters improves object initialization choices.
  • Code Reusability: Overloading constructors reduces repetition and promotes code reuse.
  • Readability: Using meaningful constructors and parameter names improves code comprehension.
  • Maintainability: Constructors are readily built and adjusted without affecting the main codebase.
  • Polymorphism: Constructor overloading allows for polymorphic behavior in Java classes.

Using this() in Constructor Overloading

In Java, the "this" keyword refers to the current object and allows you to access instance variables, and invoke methods, and constructors from the current class. It is also used to return the current class instance from a method.

Constructor Chaining

Constructor chaining is the process of calling one constructor from another based on the current object. The true goal is to transmit parameters through a variety of constructors. 

Types of Constructor Chaining

  1. Chaining within the same class
  2. Chaining with Superclass Constructors

Working of Constructor Chaining

In Java, constructor chaining occurs when one constructor calls another constructor within the same class or superclass to initialize an object, resulting in efficient code reuse and initialization.

  • Code Reusability: Allows for code reuse by calling one constructor from another, hence avoiding duplication.
  • Organization: Produces logically organized code, improving readability.
  • Flexibility: Multiple constructors can be defined with different parameters to allow for more flexible object initialization.
  • Initialization Order: Ensures that superclass initialization tasks come before individual constructor tasks, in the correct order.

Rules of Constructor Chaining

  • First statement: Constructors must begin with 'this()' or'super()'.
  • Single Call: A constructor can only call one other constructor.
  • No Circular Chains: Avoid constructor calls that generate circular chains.

Super Constructor in Java

The super constructor in Java allows a subclass to call its superclass constructor, which is necessary when inheriting and requiring specific subclass variables. Invoking super() allows for object creation with other parameters than those provided in the superclass, increasing flexibility in managing complex class hierarchies and initializing subclass instance variables.

Copy Constructor in Java

The copy constructor in Java replicates existing objects, eliminating code repetition and improving maintainability. It performs a deep copy operation, copying member variables by value rather than reference, which is important for establishing backup copies and maximizing code reuse in Java applications.

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