Constructor In Java Explained With Real-Life Examples

One of your first introductions to object-oriented programming in Java is going to be the constructor. Sounds like jargon but is really one of the simplest and most practical aspects of the language. For a fresher student beginning his feet into programming or to a career developer refreshing skill sets, constructors can simplify, enhance, and ease code maintenance written.

This blog will cover what a constructor is and its primary characteristics, what types of constructor in Java, and practical examples to illustrate that. Further, we’d discuss more advanced notions like constructor overloading in Java, constructor chaining in Java, and lesser known copy constructor in Java.

What is a Constructor in Java?

It is a block of code in Java that is invoked when you create an object. It can be considered as a welcoming gate-the moment you say new, Java will knock on the gate to establish this new object.

A constructor has no return type, not even void, like other functions. Also, a constructor’s name is exactly the same as the class’s name; so if your class was named Student, your constructor would also be named Student().

Here is an example:

class Student {

String name;

// Constructor in Java

Student() {

name = “Unknown”;

}

So, Each time you say new Student(), the constructor will run and assign the name as “Unknown”.

Features of Constructor in Java

To make the best use of the use of constructors, one should first understand great features that qualify them to do that. Here are some basic features:

Automatic Invocation

A constructor in Java is called automatically when creating an object.

No Return Type

Constructors have no value returned.

Overloadable

You can have multiple constructors in a class. This feature is called constructor overloading in Java.

Initialization

It is only a means to supply initial values for the attributes of an object.

Constructor

A constructor can be invoked by another constructor using this(). This type of invocation is called constructor chaining in Java.

Types of Constructor in Java

There are three main types of constructors in Java:

Default Constructor

This is the Zero Argument Constructor given by Java when no constructor is written at all.

class Animal {

Animal() {

System.out.println(“Animal created”);

}

Parameterized Constructor

Used when one wants to pass values while creating objects.

class Animal {

String name;

Animal(String animalName) {

name = animalName;

}

Copy Constructor in Java

This is not built-in like C++, but you can replicate it manually.

class Animal {

String name;

Animal(String animalName) {

name = animalName;

}

// Copy Constructor in Java

Animal(Animal another) {

name = another.name;

}

The copy constructor in Java will be useful when you want to clone an object state.

Constructor Overloading in Java

Say you want multiple ways to initialize an object: sometimes this way with a name, sometimes that way with a name and age, and sometimes with some default values. That is exactly where constructor overloading in Java shines.

class Book {

String title;

int pages;

// Default Constructor

Book() {

title = “Unknown”;

pages = 0;

}

// Parameterized Constructor

Book(String t) {

title = t;

pages = 100;

}

// Another Overloaded Constructor

Book(String t, int p) {

title = t;

pages = p;

}

This flexibility is what makes the constructor in Java so incredibly useful.

Constructor Chaining in Java

What else, if not, you need one constructor to use the logic of another constructor without repeating the code? That’s just what it is: constructor chaining in Java using this().

class Car {

String brand;

int speed;

Car() {

this(“Default”, 100);

}

Car(String b) {

this(b, 120);

}

Car(String b, int s) {

brand = b;

speed = s;

}

In the above example, constructors call each other, which is a very simple but powerful use of constructor chaining in Java.

class User {

String name;

int id;

String plan;

User(String name, int id, String plan) {

this.name = name;

this.id = id;

this.plan = plan;

}

This would keep your code structured and avoid those unexpected null values.

Best Practices to Remember

Always provide a default constructor if you are writing parameterized constructors too.
Use constructor overloading in Java sensibly to provide different ways to create an object.
Use constructor chaining in Java to apply code refraining.
Although Java does not support a built-in direct copy constructor in Java, a manual copy can be developed for better control of cloning.
Use descriptive parameter names to improve readability.

Real-World Use Case

You are probably creating a library app. Every time a new user is registered, you could set up a name, ID, and subscription plan along with the process. Using a constructor in Java, you would ensure that every user starts off granting all the required information right from the start.

Also Read:

Master Java with DSA

Mastering DSA with Java is the key to cracking top tech interviews and building strong problem-solving skills. PW Skills’ DSA Java course simplifies complex topics with real-world examples, making you confident in writing efficient and clean code. Whether you’re a beginner or upskilling, this course sets the foundation to excel in software development and backend roles.