Java Inheritance Example

Question

Why does the following code display "New A New B"?

class A {
public A() {
System.out.println("New A");
}
}

class B extends A {
public B() {
System.out.println("New B");
}
}

class Program {
public static void main(String[ ] args) {
B obj = new B();
}
}

/*Outputs
"New A"
"New B"
*/

Answer 1

The constructor of the super class is invoked when declaring an object of the subclass.

This must happen so variables/fields that could be extended on can be initialized.

Answer 2

simply said because the base A (parent) class must be constructed at first after that can be created the inherited class B.From that reason it was printed new A as the firts.

Answer 3

//be attentive to access modifiers
class Standard {
protected void draw() {
System.out.println("Drawing");
}

protected void write() {
System.out.println("Writing");
}
}
//fix the class
class Pro extends Standard{

protected void useEffects() {
System.out.println("Using Effects");
}

protected void changeResolution() {
System.out.println("Changing Resolution");
}
}

public class Main {
public static void main(String[] args) {
Standard standard1 = new Standard();
Pro pro1 = new Pro();

//standard version
standard1.draw();
standard1.write();

//Pro version
pro1.draw();
standard1.write();
pro1.useEffects();
pro1.changeResolution();
}
}

/*concept of the program is to change all private class to protected because private class we can't inharit*/