Java Program to Allocate and Initialize Super Class Members Using Constructor

A constructor in Java is a special method that is used to initialize an object. Whenever an object is created using the new keyword at least one construction is called. The constructor name must match with the class name and cannot have a return type. If there is no constructor available in the class in such a case java compiler provides a default constructor(no parameter constructor) by default.

Parameterized Constructor: The parameterized constructor is used to initialize the field of the class with our own values.

Example:

Java

// Parameterized Constructor Example in Java

import java.io.*;
class parameterizedConstructor {

    // fields of the class
    String name;
    int regestrationNumber;

    // creating a parameterized constructor so that we can
    // initialize the value of the class
    parameterizedConstructor(String name,
                             int regestrationNumber)
    {
        System.out.println("constructor call");
        this.name = name;
        this.regestrationNumber = regestrationNumber;
    }
}

class GFG {
    public static void main(String[] args)
    {
        // creating our first object
        parameterizedConstructor obj1
            = new parameterizedConstructor("Nilesh",
                                           2021806);
        System.out.println("Name of the student "
                           + obj1.name);
        System.out.println("Registration Number "
                           + obj1.regestrationNumber);

        // creating second object
        parameterizedConstructor obj2
            = new parameterizedConstructor("Bhaskar",
                                           2021807);
        System.out.println("Name of the student "
                           + obj2.name);
        System.out.println("Registration Number "
                           + obj2.regestrationNumber);
    }
}

Output

constructor call
Name of the student Nilesh
Registration Number 2021806
constructor call
Name of the student Bhaskar
Registration Number 2021807

In a class hierarchy constructor are called according to the hierarchy, first parent class constructor will be invoked and then the child class constructor will be invoked

Example 1

Java

// Java Program to Allocate and Initialize Super Class
// Members Using Constructor

import java.util.*;
class y {
    int b;
    int c;

    // parameterized constructor of class y
    y(int b, int c)
    {
        this.b = b;
        this.c = c;
        System.out.println("Hi I am parent constructor");
        System.out.println("multiplication of two number "
                           + b + " and " + c + " is "
                           + b * c);
    }
}
class x extends y {
    int a;

    // parameterized constructor of class x
    x(int b, int c, int a)
    {

          // calls constructor of y
        super(b, c);
        System.out.println(
            "Hi I am child class constructor");
        System.out.println("class field of x class is "
                           + a);
    }
}

class GFG {

    public static void main(String[] args)
    {
        // creating an object of class x
        // this will invoke the constructor of x
        // but before invoking the constructor of class x
        // it will invoke the constructor of it's parent
        // class which is y
        x obj = new x(3, 4, 5);
    }
}

Output

Hi I am parent constructor
multiplication of two number 3 and 4 is 12
Hi I am child class constructor
class field of x class is 5

Example 2

Java

// Java Program to Allocate and Initialize Super Class
// Members Using Constructor

import java.io.*;
class grandParent {
    int grandParentAge;
    String grandParentName;

    // constructor
    grandParent(int grandParentAge, String grandParentName)
    {
        this.grandParentAge = grandParentAge;
        this.grandParentName = grandParentName;
    }
}
class parent extends grandParent {
    int parentAge;
    String parentName;

    // parameterized constructor
    parent(int grandParentAge, String grandParentName,
           int parentAge, String parentName)
    {

          // calls grandparent constructor
        super(grandParentAge, grandParentName);
        this.parentAge = parentAge;
        this.parentName = parentName;
    }
}
class child extends parent {
    int childAge;
    String childName;

      // constructor
    child(int grandParentAge, String grandParentName,
          int parentAge, String parentName, int childAge,
          String childName)
    {

          // calls parent constructor
        super(grandParentAge, grandParentName, parentAge,
              parentName);
        this.childAge = childAge;
        this.childName = childName;
    }
    public void dispalyDetails()
    {
        System.out.println("Name of grand parent "
                           + grandParentName + " and he is "
                           + grandParentAge + " year old");
        System.out.println("Name of parent " + parentName
                           + " and he is " + parentAge
                           + " year old");
        System.out.println("Name of child " + childName
                           + " and he is " + childAge
                           + " year old");
    }
}
class GFG {
    public static void main(String[] args)
    {
        // creating an object of class child
        // this will invoke the constructor of child
        // but before invoking the constructor of class
        // child it will invoke the constructor of it's
        // parent class which is parent but parent is child
        // of grandparent class so, before invoking the
        // constructor of parent class it will invoke the
        // constructor of grandparent class
        child obj = new child(85, "Pan Singh", 39,
                              "M.S.Dhoni", 5, "Ziva Dhoni");
        obj.dispalyDetails();
    }
}

Output

Name of grand parent Pan Singh and he is 85 year old
Name of parent M.S.Dhoni and he is 39 year old
Name of child Ziva Dhoni and he is 5 year old