Answer Posted / chandra rekha
Inheritance is one of the OOPS concepts(the OOPS concepts
are Abstraction,Encapsulation,Polymorphism and Inheritance).
Java is purely a OOP language.
Inheritance is the ability of a class to use member data
and methods of another class.This is done by deriving a
class from a diff class.The class from which it derives is
called the base or the parent or super class and the class
which derives is called the derived or the child or sub
class.
Java supports two types of inheritance SINGLE inheritance
and MULTILEVEL inheritance."extends" is the keyword to
inherit properties of the base class.All the derived
classes having a single base class is termed as the single
inheritance.for example
class A
{
...
}
class B extends A
{
...
}
public class C extends A
{
...
}
this is single inheritance
whereas, a class inherits the properties of another class,
for example
class A
{
...
}
class B extends A
{
...
}
public class C extends B
{
...
}
java doesnot support multiple inheritance.However, a class
can implement any number of interfaces(interface is a
collections of methods with no definition(abstract methods))
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3.2 Consider the following class: public class Point { protected int x, y; public Point(int xx, int yy) { x = xx; y = yy; } public Point() { this(0, 0); } public int getx() { return x; } public int gety() { return y; } public String toString() { return "("+x+", "+y+")"; } } Say you wanted to define a rectangle class that stored its top left corner and its height and width as fields. 3.2.1 Why would it be wrong to make Rectangle inherit from Point (where in fact it would inherit the x and y coordinates for its top left corner and you could just add the height and width as additional fields)? (1) 8 Now consider the following skeleton of the Rectangle class: public class Rectangle { private Point topLeft; private int height, width; public Rectangle(Point tl, int h, int w) { topLeft = tl; height = h; width = w; } public Rectangle() { this(new Point(), 0, 0); } // methods come here } 3.2.2 Explain the no-argument constructor of the Rectangle class given above. 3.2.3 Write methods for the Rectangle class to do the following: • a toString() method that returns a string of the format "top left = (x, y); height = h; width = w " where x, y, h and w are the appropriate integer values. • an above() method that tests whether one rectangle is completely above another (i.e. all y values of the one rectangle are greater than all y values of the other). For example, with the following declarations Rectangle r1 = new Rectangle(); Rectangle r2 = new Rectangle(new Point(2,2), 1, 4); the expression r2.above(r1) should give true, and r2.above (r2) should give false. (You can assume that the height of a rectangle is never negative.) (2) (5)
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