Java Constructor Interview Questions

Java Constructor

Q1. How can a Java class support both default and parameterized object creation ?

A Java class can support both default and customized object creation by defining multiple constructors.

A default constructor initializes objects with default values.

A parameterized constructor allows values to be passed at the time of object creation.

This approach provides flexibility and improves usability of the class.

Example

class Book {
    String title;
    String author;

    // Default constructor
    Book() {
        this.title = "Unknown";
        this.author = "Unknown";
    }

    // Parameterized constructor
    Book(String title, String author) {
        this.title = title;
        this.author = author;
    }

    void display() {
        System.out.println("Title: " + title + ", Author: " + author);
    }
}

Using both constructors allows objects to be created with or without initial values.

Q2. What is a copy constructor in Java, and why is it used ?

A copy constructor is a constructor that takes another object of the same class as a parameter and copies its data members.

Although Java does not provide a built-in copy constructor, it can be implemented manually.

Why it is used

To create a separate object with the same data

To avoid shared references

To ensure object independence

Example

class Employee {
    String name;
    int id;

    Employee(String name, int id) {
        this.name = name;
        this.id = id;
    }

    // Copy constructor
    Employee(Employee e) {
        this.name = e.name;
        this.id = e.id;
    }
}

Both objects contain the same values but occupy different memory locations.

Q3. What is constructor chaining in Java ?

Constructor chaining is the process of calling one constructor from another constructor within the same class using this().

It helps:

Reduce code duplication

Improve maintainability

Centralize initialization logic

Example

class Student {
    String name;
    int age;

    Student(String name) {
        this(name, 18); // Calls parameterized constructor
    }

    Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

Here, the constructor with one parameter delegates initialization to another constructor.

Q4. What is the difference a constructor and a method in Java ?

Java distinguishes constructors from methods based on syntax and behavior.

Constructor	Method
Has the same name as the class	Can have any valid name
Does not have a return type	Must have a return type
Called automatically during object creation	Called explicitly
Used to initialize objects	Used to perform operations

Example

class Demo {

    Demo() { // Constructor
        System.out.println("Constructor called");
    }

    void Demo() { // Method
        System.out.println("Method called");
    }
}

Even though the method name matches the class name, the presence of a return type makes it a normal method.