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What is Constructor in Java with Example Program?

Deepak Apr 21, 2024

In the current article about what is constructor in Java with an example program, we are going to learn constructor definition, uses, and other queries related to java constructor such as constructor uses, copy constructor, java constructor interview questions, and more. So Let's start and keep learning./p>

Definition:
A constructor in Java is a Java class method that is used to initialize object attributes. it is called a class constructor implicitly when an object is created using a Java new keyword.

Constructor with Example Program:

  Employee emp = new Employee("John", 10001, "HR");

Here Object emp is created using a new keyword and its attributes are initialized by invoking the constructor as defined below.

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

And set the attributes such as name, employeeId, department from passing parameter while creating an object using the new keyword.

Key points about constructor

  • The Name of the Constructor must remain the same as the class name
  • Constructor has no return type.
  • Constructor is implicitly called when an instance is created using a new keyword.
  • Compiler creates default constructor in case there is no existence of constructor code block defined in the class.

Demonstration of what is constructor in Java with example program as below

 public class Employee {

    private String name;

    private int employeeID;

    private String department;

    public Employee(String name, int employeeID, String department) {
        this.name = name;
        this.employeeID = employeeID;
        this.department = department;
    }

    

    public void showEmployeeInfo() {

        System.out.println("Name : " + this.name); 
        System.out.println("EmployeeID : " + this.employeeID);
        System.out.println("Department : " + this.department);
    }

    public static void main(String[] args) {

        Employee emp = new Employee("John", 10001, "HR");

         System.out.println("Display Employee details  initialized via constructor.");
        // Show Employee details  initialized via constructor 
        emp.showEmployeeInfo();

    }

Output:

 Name: John
EmployeeID: 10001
Department: HR

What is a Copy Constructor In Java and Why do we need Copy Constructor?

A Copy Constructor is a constructor mechanism in a Java class that is used to create an object initialized with another Java class object of the same class. Read What is a Copy Constructor In Java for more detailed explanation with example program.

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Contributed By

Deepak

Deepak

QC STAFF
51 Posts
  • PHP
  • JAVA
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