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In Java, the constructor is a block of codes similar to the method. The constructor is called when the instance of the object is created. The constructor is a special method which is used to initialize the object.

• The constructor doesn’t have any return type.
• The constructor name must be same as the class name.

There are two types of Constructors In java.

• Default Constructor –  When a constructor doesn’t have any parameter then it is called default parameter. If there is no constructor in the class then the compiler automatically creates a default constructor.
• Parameterized constructor – If a constructor has a specific number of parameters then it is called the parameterized constructor.

class DConst
{
DConst()
{
System.out.println("Default Constructor called");
}
public static void main(String args[])
{
DConst d1=new DConst();
}
}
Output:
Default Constructor called

Program to print the default values of the default constructor –    

class Student
{  
int rno;  
String name;  
  
void display()
{
System.out.println(rno+" "+name);
}  
 
public static void main(String args[])
{  
Student s1=new Student();  
Student s2=new Student();  
s1.display();  
s2.display();  
}  
}
Output:
0 null
0 null

• Program For Parameterized Constructor – 

class Student
{  
int rno;  
String name;  
      
Student(int i,String n)
{  
rno = i;  
name = n;  
}  
void display()
{
System.out.println(rno+" "+name);
}    
public static void main(String args[])
{  
Student s1 = new Student(101,"Tanmay");  
Student s2 = new Student(102,"Shivam");  
s1.display();  
s2.display();  
}  
}
Output:
101 Tanmay
102 Shivam 

Constructor Overloading:

If the constructor with the same name but different in the number of parameters in a class is called constructor overloading.

class Student
{  
int rno;  
String name;  
int age;  
    
Student(int i,String n)
{  
rno = i;  
name = n;  
}  

Student(int i,String n,int a)
{  
rno = i;  
name = n;  
age=a;  
}  
void display()
{
System.out.println(rno+" "+name+" "+age);}  
public static void main(String args[]){  
Student s1 = new Student(100,"Tanmay");  
Student s2 = new Student(101,"Shivam",17);  
s1.display();  
s2.display();  
}  
}
Output:
100 Tanmay 0
101 Shivam 17