Constructors in Java

constructor in java is a spacial method, that is called when object is created. Its main purpose is to initialize the object. It is used to set default or user-defined values for the object's attributes.

• A constructor has the same name as the class.
• It does not have a return type, not even void.
• It can accept parameters to initialize object properties

Rules of Constructor

• Constructor name must be the same as the class name.
• Constructors do not have a return type (not even void).

• If you add a return type, it becomes a method, not a constructor.

• A constructor is called once per object creation (when using new).

• If no constructor is defined, Java provides a default no-arg constructor.

• If you define any constructor, the default is con't provided.

Default Constructor :

Java provides this automatically if you don’t define any constructor

public class Constructor{
int age=10;
public static void main(String[] args){
Constructor obj = new Constructor();
System.out.println(obj.age);
}
}

No-Argument Constructor

You write it yourself, no parameters.

public class Constructor{
int age=10;
public Constructor(){
System.out.println("no agru constructor");
}
public static void main(String[] args){
Constructor obj = new Constructor();
System.out.println(obj.age);
}
}

Parameterized Constructor

Used to pass values at object creation and set value for arttibutes.

public class Constructor{
int age;
public Constructor(int a){
age=a;
}
public static void main(String[] args){
Constructor obj = new Constructor(19);
System.out.println(obj.age);
}
}