What is constructor overloading in Java?

Constructor

Constructor is a special type of method used for object initialization of a class.

Compiler provides a default constructor if we don’t have any constructor in the class. They are invoked implicitly.

There are 2 types of constructors:

Default constructors
Parameterized constructors

There are some rules for creating a constructor in Java:

Constructor name should be the same as the class name.
Constructor shouldn’t have any explicit return type.
Constructor cannot be abstract, static, final, and synchronized.

Constructor overloading

Constructor overloading involves having more than one constructor with different parameters.

This is done to make every constructor perform a specific task.

Differences in parameters make the compiler understand that every constructor is different from another.

Code

Let’s take a look at the code snippet below.

class Container
{
double length,breadth,height;
     Container(double l, double b, double h)
     {        
          length = l;
          breadth = b;
          height = h;
     }
     Container()
     {
          length=breadth=height=0;
     }
     Container(double side)
     {
          length=breadth=height=side;    
     }
double volume()
{
   return length*breadth*height;
}
}
class Main
{
public static void main(String args[])
{
    Container cuboid = new Container(3, 4, 8);
    Container nonebox = new Container();
    Container cube = new Container(12);
double vol;
    vol = cuboid.volume();
       System.out.println(" Volume of cuboid is " + vol + " cubic unit");
    vol = nonebox.volume();
       System.out.println(" Volume of nonebox is " + vol + " cubic unit");
    vol = cube.volume();
       System.out.println(" Volume of cube is " + vol + " cubic unit");
}
}

Explanation

In line 1, we create a class named Container.
In line 3, we declare variables of double type.
In lines 4 to 9, we create the first parameterized constructor in which we assign all double type parameters to the declared variables of the class respectively.
In lines 10 to 13, we create a second constructor with no parameters in which we assign 0 to all the variables of the class.
In lines 14 to 17, we create a third constructor with one double type parameter and assign the parameter to all the variables of the class.
In lines 19 to 22, we define a method which returns the volume of the container with the help of the values of the variables of the class.
In lines 25 and 27, we initialize a Main class and a main function.
In lines 29 to 31, we create the object of the Container class and initialize them with the help of constructors.
In lines 34 to 39, we call the method of Container class and displayed the value stored in the double type variable.

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