Constructor's in java

Shreyesh kolhe
November 18, 2021

 A constructor is similar to a method (but not actually a method ) that is invoked automatically when an object is instantiated.

class Test {
     Test(){
         //constructor body 
     } 
} 

for Ex.

public class MyConstructor {
    MyConstructor() {
        System.out.println("Object is now created");
    }

    public static void main(String args[]) {
        MyConstructor obj = new MyConstructor();
    }
}
Object is now created

No-Arg(argument) Constructors

    if a java constructor does not accept any parameters, it is a no-arg constructor.

class Test{
int a;
Test(){
a=5;   //initialize here
}
}

public class Vehicle {
    int wheels;

    Vehicle() {
        wheels = 4;
    }

    public static void main(String args[]) {
        Vehicle car = new Vehicle();

        System.out.println(car.wheels + " wheels");

    }
}
 4 wheels

Parameterized Constructors
    If a Java constructor accepts some parameters, it is a parameterized constructor.
Ex.
class Test {
        int a;
         Test ( int b ) {
                a = b;     // initialize here
    }
}


public class Vehicle {
    int wheels;

    Vehicle(int noOfWheels) {
        wheels = noOfWheels;
    }

    public static void main(String args[]) {
        Vehicle car = new Vehicle(6);
        Vehicle scuty = new Vehicle(2);

        System.out.println(car.wheels + " wheels");
        System.out.println(scuty.wheels + " wheels");

    }
}
PS G:\oops> java Vehicle      
6 wheels
2 wheels

Constructors Overloading
    Similar like method overloading, you can also overload constructors if two or more constructors are different in parameters.

class Test {
        int a; 
        Test () {
                    a = 5;        //initialize here
}
Test ( int b) {
            a = b;           //initialize here
    }
}

    
public class Vehicle {
    int wheels;
    String color;

    Vehicle(int noOfWheels) {
        wheels = noOfWheels;
    }

    Vehicle(int wheels, String color) {
        this.wheels = wheels;
        this.color = color;

    }

    public static void main(String args[]) {
        // Vehicle car = new Vehicle(6);
        // Vehicle scuty = new Vehicle(2);
        Vehicle truck = new Vehicle(12, "red");

        // System.out.println(car.wheels + " wheels");
        // System.out.println(scuty.wheels + " wheels");

        System.out.println(truck.wheels + " wheels and color = " + truck.color);

    }
}
12 wheels and color = red