Constructors in Java

Constructors are special methods in a class that are automatically invoked when an instance of the class is created. The main role of constructors is to initialize the instance variables of a class.

In Java, constructors share the same name as the class and don't have a return type.

Types of Constructors:

1. Default Constructor:

• A default constructor is a constructor that is automatically generated by the compiler if no constructor is explicitly defined in the class.
• It has no parameters and initializes the data members to their default values.
• The default constructor is invoked when an object is created without any arguments.

Example:

class MyClass
{
    private int data;

    // Default constructor (automatically generated if not defined)
    public MyClass()
    {
        data = 0;
    }
}

 

In the above example, the `MyClass` has a default constructor that initializes the `data` member to zero.

2. Parameterized Constructor:

• A parameterized constructor is a constructor that takes one or more parameters.
• It allows you to initialize the data members of an object with specific values provided at the time of object creation.

Example:

class Rectangle
{
    private int length;
    private int width;

    // Parameterized constructor
    public Rectangle(int len, int wid)
    {
        length = len;
        width = wid;
    }
}

In the above example, the `Rectangle` class has a parameterized constructor that takes the length and width as parameters and initializes the corresponding data members.

Constructor Overloading:

Constructor overloading refers to the ability to define multiple constructors within a class, each having a different parameter list. The compiler determines which constructor to invoke based on the arguments provided during object creation.

Example:

class Employee
{
    private String name;
    private int age;
    private double salary;

    // Default constructor
    public Employee()
    {
        name = "";
        age = 0;
        salary = 0.0;
    }

    // Parameterized constructor with three arguments
    public Employee(String newName, int newAge, double newSalary)
    {
        name = newName;
        age = newAge;
        salary = newSalary;
    }
}

In the above example, the `Employee` class demonstrates constructor overloading. It has a default constructor and a parameterized constructor. These constructors allow creating `Employee` objects with different initialization options.