Constructor in Java programming language

When Java programs are compiled, a constructor is automatically called.

Syntax of default constructor

classname()
{

}

Example of default constructor

class cons{
cons()  //this is constructor(constructor name is equalant to class name) 
{
}
}

 We can means, no – argument constructor looks like  default constructor but it contains block of code in the body section.
Ex

class cons
{

public cons()  //this is constructor(constructor name is equivalent to class name) 
{
System.out.println(“This is a demo of default cons”);
}
public static void main(String args[]){
cons disp=new cons(); //creating object
}

}
In this case, this is an example of constructor. Here, we created a class named cons and created a constructor with the same name. This is a no-arg constructor in the cons class. Constructor is called when an object is created. As you can see, the following output “This is a demo of default cons” is displayed.

No-argument constructor displays default value

No-argument constructor(default constructor) provides the default value to the object 0, null. This depends on the data type.

class studetail
{
int id;   //global variable
String name;
int marks;

studetail()  //this is constructor name same  as class name
{
System.out.println(“my name is “+name);
System.out.println(“my id is “+id);
System.out.println(“my marks is “+marks);

}
public static void main(String args[]){
studetail stu=new studetail(); //object for constructor
}

}

In the class above, we have created a constructor ,studetail class. But, it doesn’t have any parameter or any argument. So constructor displays the default value.

parameterized  constructor

A constructor that has one or more parameters is called parameterised constructor.

class stu
{
int marks;  //global variable
int id;
String name;

stu(int id1, int marks1, String name1)  // parameter passing to constructor
{
id=id1;
marks=marks1;  //assign local variable to global variable 
name=name1;

}

void display(){
System.out.println(“my name is”+name);
System.out.println(“my id is”+id);
System.out.println(“my marks is”+marks);
}

public static void main (String args[])
{
stu my=new stu(24,1,”vannan”); //passing argument to parameter
my.display();
}
}

Using this keyword in the constructor in java

Program

class studentm
{
int marks;  //global variable
int id;
String name;

studentm(int id, int marks, String name)  //this is constructor name same  as class name with parameter
{
this.id=id;
this.marks=marks;
this.name=name;

}

void display(){  //method with return type
System.out.println(“my name is “+name);
System.out.println(“my id is “+id);
System.out.println(“my marks is “+marks);
}

public static void main (String args[])
{
studentm my=new studentm(24,1,”vannan”);  // passing argument for parameter
my.display();
}
}

Constructor overloading in java        Method in Java             Method Overloading in Java

Abstraction in C++                                                                    Abstraction in Java

Encapsulation in C++                                                             Encapsulation in Java

Polymorphism in C++                                                          Methodoverriding in Java

Method overloading in Java                                                Constructor overloading in Java

Exception Handling in Java