Constructors in Java

 Constructors in Java

  • In Java, a constructor is a block of codes similar to the method. 

  • It is called when an instance of the class is created. 

  • At the time of calling constructor, memory for the object is allocated in the memory.

  • It is a special type of method which is used to initialize the object.

  • Every time an object is created using the new() keyword, at least one constructor is called.

  • It calls a default constructor if there is no constructor available in the class. In such case, Java compiler provides a default constructor by default.
  • There are two types of constructors in Java: no-arg constructor, and parameterized constructor.
  • Note: It is called constructor because it constructs the values at the time of object creation. It is not necessary to write a constructor for a class. It is because java compiler creates a default constructor if your class doesn't have any.

Rules for creating Java constructor:-

There are two rules defined for the constructor.

  1. Constructor name must be the same as its class name

  2. A Constructor must have no explicit return type

  3. A Java constructor cannot be abstract, static, final, and synchronized

Types of Java constructors:-
  1. no-arg constructor or Default constructor
  2. parameterized constructor.
Java Default  Constructor:-

A constructor is called "Default Constructor" when it doesn't have any parameter.

Syntax of default constructor:

<class_name>() Example:- Test()

 {Code}                                                {Cod}    

Example of default constructor:-

class Bike1

{    

Bike1()  

{

System.out.println("Bike is created");

}  

 public static void main(String args[]){   

Bike1 b=new Bike1();  

}  

}  

Java Parameterized Constructor:-

  • A constructor which has a specific number of parameters is called a parameterized constructor.

Syntax of Parameterized Constructor:-
<class_name>(Args)
{
code;
}

Ex:-
Test(int i , int j)
{
code ;
}
Example of Parameterized Constructor:-

class Student4{ 

    int id;  

    String name;  

    Student4(int i, String n){  

    id = i;  

    name = n;  

    }  

    

    void display(){System.out.println(id+" "+name);}  

   public static void main(String args[]){  

      Student4 s1 = new Student4(111,"om");  

    Student4 s2 = new Student4(222,"priya");  

    s1.display();  

    s2.display();  

   }  

}  

Constructor Overloading in Java:-

  • In Java, a constructor is just like a method but without return type. It can also be overloaded like Java methods.

  • Constructor overloading in Java is a technique of having more than one constructor with different parameter lists. 

  • They are arranged in a way that each constructor performs a different task. 

  • They are differentiated by the compiler by the number of parameters in the list and their types.


Example of Constructor Overloading in Java:-

class Student5{  

    int id;  

    String name;  

    int age;   

    Student5(int I, String n)

{  

    id = i;  

    name = n;  

    }  

     Student5(int I, String n, int a)

{  

    id = i;  

    name = n;  

    age=a;  

    }  

    void display(){System.out.println(id+" "+name+" "+age);}  

   

    public static void main(String args[]){  

    Student5 s1 = new Student5(111,"Karan");  

    Student5 s2 = new Student5(222,"Aryan",25);  

    s1.display();  

    s2.display();  

   }  

}  




                                                                 










Comments

Post a Comment

Popular posts from this blog

Java Package

  Java Package A java package is a group of similar types of classes, interfaces and sub-packages. Package in java can be categorized in two form, built-in package and user-defined package. There are many built-in packages such as java, lang, awt, javax, swing, net, io, util, sql etc.  Advantage of Java Package Java package is used to categorize the classes and interfaces so that they can be easily maintained. 2) Java package provides access protection. 3) Java package removes naming collision.  s imple example of java package package mypack;   public class Simple{     public static void main(String args[]) {       System.out.println("Welcome to package");      }   } How to access package from another package? There are three ways to access the package from outside the package. import package.*; import package.classname; fully qualified name.      1) Using p...
Read more

Life cycle of a Thread and creating thread class

Image
  Life cycle of a Thread /Thread States:         A thread can be in one of the five states. According to sun, there is only 4 states in thread life cycle in java new, runnable, non-runnable and terminated. There is no running state.The life cycle of the thread in java is controlled by JVM. The java thread states are as follows: New Runnable Running Non-Runnable (Blocked) Terminated 1) New The thread is in new state if you create an instance of Thread class but before the invocation of start() method. 2) Runnable The thread is in runnable state after invocation of start() method, but the thread scheduler has not selected it to be the running thread. 3) Running The thread is in running state if the thread scheduler has selected it. 4) Non-Runnable (Blocked) This is the state when the thread is still alive, but is currently not eligible to run. 5) Terminated A thread is in terminated or dead state when its run() method exits. ...
Read more

Inheritance in Java

Image
  Inheritance in Java Inheritance is an important pillar of OOP(Object Oriented Programming).  It is the mechanism in java by which one class is allow to inherit the features(fields and methods) of another class. Important terminology:- Super Class: The class whose features are inherited is known as super class(or a base class or a parent class). Sub Class: The class that inherits the other class is known as sub class(or a derived class, extended class, or child class). The subclass can add its own fields and methods in addition to the superclass fields and methods. Reusability: Inheritance supports the concept of “reusability”, i.e. when we want to create a new class and there is already a class that includes some of the code that we want, we can derive our new class from the existing class. By doing this, we are reusing the fields and methods of the existing class How to use inheritance in Java:- The keyword used for inheritance is extends . Syntax : class derived-class ext...
Read more