Meaning of keywords super and extends

Question

Problem 1:

 class Shape {
 int noOfShape;
 Shape() //Constructor
 {
   System.out.println(“Shape constructor”);
 }
  Shape(int s) //Constructor
 {
    noOfShape = s;
 System.out.println(“Shape=“+noOfShape);
 }
}
class Rectangle extends Shape {
 int noOfRectangle;
  Rectangle()  // Constructor
 {
 super(99);
 System.out.println(“Rectangleconstructor”);
 }
 Rectangle(int r) //Constructor
 {
  noOfRectangle = r;
 System.out.println(“Rectangle =“+noOfRectangle);
 }
}
class Box extends Rectangle {
 int noOfBox;
  Box(int b)  // Constructor
 {
  noOfBox = b;
 System.out.println(“Box =“+noOfBox);
 }
}
class testMain {
  public static void main(String arg[])
 {
    Box b1 = new Box(10);
    Rectangle r1 = new Rectangle(20);
    Shape s1 = new Shape(30);
    Rectangle r2 = new Rectangle();
    Shape s2 = new Shape();
 }
 }

Questions:

Question1. Define the term constructor. Using the above Java program explain constructor chaining.

Question2. Explain the declaration: Rectangle r1 = new Rectangle (20).

Question3. What is the meaning of keywords super and extends?

Question4. What is the output of above Java program?