CBSE Book Class 12 Informatic Practices Advanced Programming

Learning Objectives

After studying this lesson the students will be able to:

   Define objects and their usage

   Appreciate the usage of native classes Math and String

   Understand the need and use of methods pow() and round() of Math class

   Understand the need and use of methods toUpperCase(),

   toLowerCase(),substring(), concat(), length() and trim() of String class

   Develop small applications involving the methods learnt of Math and String classes.

In the last lesson, we introduced the concept of Object Oriented Programming and learnt about the different elements of an Object Oriented Programming Language. Now we will move on to learn about two important classes we commonly use in Java - namely Math and String. The lesson focuses on how to use some of the popular methods of these classes appropriately and appreciate how they simplify many programming tasks for us.

Find a 9-digit number, which you will gradually round off starting with the number placedat units, then tens, hundreds etc., until you get to the last numeral, which you do not round off. The rounding alternates (down, up, down ...) which means that the first number from the right is rounded down while the second number from the right is rounded up and so on. After rounding off 8 times, the final number is 500000000. The original number is commensurable by 6 and 7, all the numbers from 1 to 9 are used, and after rounding four times the sum of the not rounded numerals equals 24.

Classes and Objects

As studied in the previous lesson, a class is used to encapsulate data and methods together in a single unit. An object is an instance of a class that is capable of holding actual data in memory locations. Class and objects are related to each other in the same way as data type and variables. If we take a hypothetical case in which human is a class, Mr. Shah and Mr. Kumar will be the objects of this Human class.

Math Class

The Math class contains built-in methods for performing basic numeric operations such as the elementary exponential, rounding of a number, square root, and trigonometric functions. These functions can be used directly by the user in the program. These methods are highly reliable and can tremendously reduce the amount of coding required for an application.

It is not necessary to import any package for the Math class because this is already in the java.lang package. Therefore in-built methods of the Math class can be used directly in the application just like the other methods, as we have learnt in the previous class. Let us learn the usage of these methods by building some simple applications. First let us create an application that calculates the power of a number. Observe the following form carefully.

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