Constructors

Important notes

• Constructors are invoked implicitly when you instantiate objects.
• The two rules for creating a constructor are:
  • A Java constructor name must exactly match with the class name (including case).
  • A Java constructor must not have a return type.
• If a class doesn't have a constructor, Java compiler automatically creates a default constructor during run-time. The default constructor initialize instance variables with default values. For example: int variable will be initialized to 0
• Constructor types:
  • No-Arg Constructor - a constructor that does not accept any arguments
  • Default Constructor - a constructor that is automatically created by the Java compiler if it is not explicitly defined.
  • Parameterized constructor - used to specify specific values of variables in object
• Constructors cannot be abstract or static or final.
• Constructor can be overloaded but can not be overridden.

class Company {

    String domainName;

    public Company(){
        this.domainName = "default";
    }

    public Company(String domainName){
        this.domainName = domainName;
    }

    public void getName(){
        System.out.println(this.domainName);
    }

    public static void main(String[] args) {
        Company defaultObj = new Company();
        Company programizObj = new Company("programiz.com");

        defaultObj.getName();
        programizObj.getName();
    }
}

When you run the program, the output will be:

default
programiz.com