Programa Java para asignar e inicializar miembros de superclase usando Constructor

Un constructor en Java es un método especial que se usa para inicializar un objeto. Cada vez que se crea un objeto usando la nueva palabra clave, se llama al menos una construcción. El nombre del constructor debe coincidir con el nombre de la clase y no puede tener un tipo de retorno. Si no hay un constructor disponible en la clase, en tal caso, el compilador de Java proporciona un constructor predeterminado (sin constructor de parámetros) de forma predeterminada.

Constructor Parametrizado: El constructor parametrizado se utiliza para inicializar el campo de la clase con nuestros propios valores.

Ejemplo:

// 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);
    }
}

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

En una jerarquía de clases, los constructores se llaman de acuerdo con la jerarquía, se invocará el primer constructor de la clase principal y luego se invocará el constructor de la clase secundaria.

Ejemplo 1

// 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);
    }
}

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

Ejemplo 2

// 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();
    }
}

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