Computer

Chapter: 4

Introduction to Programming with C++ & Java

[Till Pg. No. 75]

Learning Objectives

Introduction to object-oriented programming

Starting C++ with turbo C++ [Omit]

Starting Java with BlueJ

Components of a Program (Java)

Data types

Declaration & initialization of variables

Operators

Introduction to Object-Oriented Programming

All operations performed by a computer are controlled by computer programs. A

computer program is a program code which involves the use of a computer

programming language to write a series of instructions or algorithms.

The modular and structured approach to programming was followed before the

development of object-oriented programming. However, a need for new

methodology grew with the increasing size and complexity of programs. This gave

rise to the object- oriented programming (OOP) methodology which had the best

features of structured programming with several new concepts.

In an object-oriented programming language like C++ and Java, the data and the

functions are defined that act upon the data. The major features of object-oriented

programming are:

Object Class

Data Hiding Data Abstraction

Encapsulation Polymorphism

Inheritance

OBJECT

An object is the basic element of object - oriented programming. Let us look at

some of the real - world entities or objects around us - the trees, people, animals,

birds, even your computer, a mug or a spoon - all are examples of objects. Each

object has its own set of characteristics and behaviors.

For example, let us consider a plant. Its characteristics would be the name, color of

its leaves, its type, flowering or non - flowering and so on. And, its behaviour

would be - producing flowers, producing fruits, shedding leaves and so on.

Similarly, the characteristics of a computer will be - its type, size, speed, amount

of RAM and so on. And its behavior will include - processing data, playing music,

showing images, playing movies and so on. Hence, we can say that an object

encapsulates characteristics and behaviour.

Here, the plant belongs to living things category. As plants and animals are objects

belong to the type of living things. So, living things is called a class here.

An object in object - oriented programming, comprises of data and code that

operate on that data. In other words, an object can be defined as a group of data

members or attributes as characteristics and related methods, routines or

member functions as its behavior. One particular object is called an instance.

CLASS

A group of objects that share similar characteristics (attributes) and behaviour

(methods) form a class. As explained in the above example, the plant is an object

and it belongs to the living things class. Let us take another example, consider an

animal. One way to visualize an animal is through its specie, its color, its weight,

its height and so forth. Another way is to think about what it does: it moves, it

eats, and it produces sound and so on. Therefore, the class of an animal

encapsulates its various attributes and its functions together into a single collection

called an object. A program can contain any number of classes.

DATA HIDING

The object can maintain private data and methods that can be changed at any time

without affecting the other objects that depend on it. This is called data hiding or

information hiding. The public data and methods are accessible to all the classes

in the program. And the private data and methods are accessible only within the

class in which they are declared and remain hidden from all the other classes in the

program.

DATA ABSTRACTION

Data abstraction can be defined as a process through which the programmer hides

all but the relevant data about an object. This reduces complexity and increases

productivity. We can also say that abstraction also defines an interface for our

applications.

ENCAPSULATION

Encapsulation, closely related to data hiding, allows binding of code and the data

together into a class) and restricts any outside entity from misusing them. A class

in the object - oriented programming is an example of encapsulation.

POLYMORPHISM

Poly means many, whereas, morph means forms. Polymorphism in a

programming language is the ability to make use of objects time and again without

knowing their exact type at the compile time. You know that a class is a collection

of data members and the member functions that operate on these data members.

Since polymorphism refers to the same name given to many forms, these forms

may be classes or functions.

A very simple real life example of polymorphism would be that of a person who

could speak various languages, such as Hindi, English and Malayalam. Here, the

act of speaking is the method. However, considering this particular person

(object), this method (speaking) would have various forms - speaking Hindi,

speaking English or speaking Malayalam.

INHERITANCE

Inheritance is a feature of a programming language in which one object can attain

classes. Like, multiple classes can be created in other programs. This might result

in similar classes being defined across different programs, to handle similar

requirements. Therefore, to extend new classes from existing ones, the

programming language has the feature of inheritance, in which one class can be

derived from another existing class, leading to the reuse of existing code. This

feature again reduces complexity and increases productivity.

Starting JAVA with BlueJ

BlueJ is a Java integrated development environment (IDE), specifically designed

for teaching at an introductory level. It was designed and implemented by the

BlueJ team at Monash University at Melbourne in Australia, and the University of

Southern Denmark at Odense. It can be freely downloaded from

http://www.bluej.org/.

http://www.bluej.org/

To start BlueJ, follow the steps given below.

Step 1: Click on the Start button All Programs BlueJ BlueJ.

Or

Double-click the shortcut icon of BlueJ located on the desktop. The

BlueJ window will appear on the screen (Fig. 1).

Fig. 1: BlueJ Window

You need to create a Project in order to write a Java program in BlueJ.

Step 2: Click on the Project New Project…(Fig. 2). A New Project dialog

box will appear where you can set the path and the name for your

project (Fig. 3).

Fig. 2 New project option of the Project menu

Fig. 3 New Project dialog box

Step 3: Click on the Create/ Choose button (Fig. 3). This will create your folder

at the location mentioned and open the project window.

Step 4: The project window has one file by default. This is a readme file where

you can record your notes. Just double-click on the icon to open the

file (Fig. 4).

Fig. 4 Project window with readme file

Fig. 5 Readme editor window

Step 5: An editor window will appear where you can type text. Click on the

Close button to close the file once you are done (Fig. 5).

Step 6: Now, to create a class in your project, click on the New Class... button

(Fig. 6).

Fig. 6 Selecting New Class

Or

Select Edit New Class… option.

A Create New Class dialog box will appear where you can type the

name for your class (Fig. 7).

Step 7: Click on the OK button (Fig. 7). This will bring a new icon in the

project window. This icon will denote the new class created. This

class file will contain the default code. Also, the stripes on the file

icon tell that the file has not been compiled even once (Fig.8 ).

Fig. 7 Create New Class dialog box

Fig. 8 New icon created for Class FirstJavaProgram

Step 8: Double-click on the file icon to open the file. It will open in the editor

window. Here, you can make the desired changes or you can delete the

default code and write your own code afresh (Fig. 9).

Fig. 9 Program template in BlueJ

Step 9: Type the sample program code (Fig. 10).

public class FirstJavaProgram

{

public static void main()

{

System.out.println(“I like JAVA programming”);

}

}

Fig. 10 Sample program in the Editor window of Class FirstJavaProgram

Fig. 11 Saving the Class

Step 10: Click on the Class Save option to save the code (Fig. 11).

Structure of JAVA Program

Let us examine the sample program (Fig. ) for creating a Class in JAVA to

understand the basic structure of a JAVA program.

public class FirstJavaProgram

It declares a class called FirstJavaProgram

public static void main()

It declares a method called main(). Most of the actual code in Java is

found within methods. This method or function is the parent function of

all the functions in Java. It is executed when the Class FirstJavaProgram

is executed using the Java command.

System.out.println(“I like JAVA programming”);

It prints “Ilike JAVA programming” to the output screen. println means

string or text provided in the brackets and then add a line break, like the

enter key.

The remaining lines having opening and closing curly brackets or braces

close the method and the class.

Compiling a JAVA Program

After you write the source code in BlueJ, next step is to compile the code

and check for errors, if any. To compile a program source file, follow the

steps given below.

Step 1: Click the Compile button (Fig. 12).

Or

Right-click on the class file FirstJavaProgram icon and click on the

Compile option from the context menu.

After compilation, the stripes will disappear from the icon (Fig. 13).

Fig. 12 Program after compilation

Fig. 13 Compile class file

Running a JAVA Program

After you have compiled your code successfully without any errors, you can

execute it.

To observe the output of the code, follow the steps given below.

Step 1: Right click on the class file FirstJavaProgram icon and select the void

main() option (Fig. 14).

Step 2: A method call will be made to the main function and the output will

appear in the Terminal Window (Fig. 15).

Fig. 14 Right-click the Class icon Fig. 15 Program output

Tokens

A token is the smallest individual unit of a program. C++ and Java support the

following types of tokens.

Keywords

Identifiers

Constants

Punctuators

Comments

Operators

Keywords

Keywords are the reserved words that form the vocabulary of any programming

language. Hence, they are also known as reserved words. They have special

meanings and usage. C++ and Java keywords are case-sensitive and should be

typed in lowercase only. Some examples of keywords are int, do, return, if and

continue.

The keywords have special meanings to the language compiler. These reserved

words are meant for special purposes only and should not be used as identifiers.

Identifiers

An identifier is a sequence of characters (letters, numbers and underscore) that we

create to denote a name to any class, object or function.

Rules to create identifiers

Identifiers are case sensitive

An identifier cannot be a keyword or true or false, or null.

An identifier can consist of letters, digits 0-9, the underscore, or the dollar

sign.

An identifier must start with a letter, an underscore, or a dollar sign.

Identifier cannot start with a digit but digits can be used after the first

character.

We cannot use symbols or spaces in the names of the identifiers.

Naming Conventions

Identifiers should be meaningful. For example, if an identifier is going to

store the value of a student’s fee, it should be ideally named as “studentfee”

than simply “f” though is correct.

If more than one word is used in the name of a variable, first word should be

all small case and the first letter of the consequent words should be capital

like studentName, dateOfBirth and so on.

The names of the public methods and instance variables should begin with

lower case letter.

Private and local variables should use lower case letters, for example,

areacircle, tot_marks and so on.

Class names should be named using all uppercase letters and an underscore,

for example, MAX_VAL, TOTAL and so on.

Data Types

Data in any programming language is handled in a systematic manner. For this

purpose, it is divided into various types. C ++ and Java too defines its data into

various types. Some of the data types supported by C ++ and Java are- void, char,

int, float and double. Data types are initialized to some default values when they

are declared. The table 1 given below lists some of the common data types

available in C ++ and Java.

Table1: Some common data types available in C++ and Java

Data type Description Storage

void Void or Null 0 byte

char A single character 1 byte

int Integer 4 bytes

float Single precision floating point (that is, can

display 7 digits after the decimal point)

4 bytes

double Double precision floating point (that is, can

display 15 digits after the decimal point)

8 bytes

VARIABLES AND CONSTANTS

Variables are the names that represent or store constant values. For example, age =

16. Here, 16 is the constant value which is stored in the variable named age.

As the name suggests, a variable may change its value from time to time.

Therefore, we can define a variable as a memory location (s) that is named and

which is used to store a constant. Hence, these memory locations store a value of

certain type. The variable may store its value in one or more cells depending upon

the type of the value.

When a variable is defined in a program, the compiler determines its data type

(integer, float, character and so on) and sets aside the appropriate amount of

memory for the value of the variable to be stored. Suppose, a variable named

my_var is of float type (which is four bytes long) and as each cell is one byte

large, the compiler for this variable will set aside four bytes of memory.

It is now clear that variables have a name (identifier), a type (data type), and a

value. Before we try to use a variable, we have to declare and initialize it. When

we declare a member of a class as static, it means no matter how many objects of

the class are created, there is only one copy of the static member.

Declaring Variables

Variables have a significant role in programming as their declaration allows

programmers to write flexible programs. Instead of entering data directly into a

program, a programmer can use variables to represent the data. During the

program execution, the variables are replaced with real data. This makes it

possible for the same program to process different sets of data. A variable in C ++

and Java is declared by specifying its data type.

The syntax to declare a variable in C ++ and Java is as follows:

data_type variable_name;

Example :

int age;

float marks;

Note that several variables of the same data type can be declared in the same line

separating the variable identifiers with commas.

Example :

int x, y, z;

The above statement has exactly the same meaning as:

int x;

int y;

int z;

Initialisation of Variables

After a variable is declared, it could be assigned some value. This is accomplished

using the assignment operator (=).

The syntax is as follows:

data_type variable_name;

variable_name = value;

When a variable is declared and assigned a value in single statement, it is

initialised.

data_type variable_name = value;

For example,

Data Type Variable Name Assignment Operator Value

Multiple variables can be declared and initialized in a single statement, as shown

below.

For example, int weight = 32, height = 160;

It is not mandatory to initialize all the variables when they are declared.

int age = 13

For example, int weight, height = 160;

Operators

Operators help in forming a defined link between the variables and constants. The

variables and constants are called operands. The number of operands required by

the operator can classify operators. For example, unary operators have only one

operand (for example, -1, +40) and binary operators have two operands required

operator and operands together form an expression.

There are many types of operators defined in C ++ and Java. Some of them are as

follows:

Arithmetic Operators (+, -, *, /, % )

Relational Operators (=, ==, ! =)

Logical Operators (||, &&, !)

Assignment Operator (=)

Let us learn about them in detail.

Arithmetic Operators (+, -, *, /, %)

Arithmetic operators are used in mathematical expressions. The table 2 given

below lists all the arithmetic operators.

Table 2: Arithmetic Operators

Operator Name Example with X=20

& Y=10

Description

+ Addition or

Unary plus

X+ Y will return 30 Adds value on either side of the

operator

- Subtraction or Unary minus

X-Y will return 10 Subtracts right hand operand from the left hand operand

* Multiplication X*Y will return 200 Multiplies values on either side

of the operator

/ Division X/Y will return 2 Divides left hand operand by

right hand operand and returns

quotient

% Modulus X%Y will return 0 Divides left hand operand by right hand operand and returns

remainder

Relational Operators (=, ==, !=)

Relational operators are used to compare two expressions. The result can be either

true or false. The table 3 below lists all the relational operators available in C++

and Java.

Operator Name Example with X=20

& Y=10

Description

< Less than X= Greater or equal

than

X>=Y will return TRUE Compares both the operands

and returns true if the left

operand is greater than or equal

to the right operand, otherwise returns false

== Equal to X==Y will return

FALSE

Compares both the operands

and returns true if both the

operands are equal, otherwise returns false

!= Not equal to X!=Y will return TRUE Compares both the operands and returns true if both the

operands are not equal,

otherwise returns false

Logical Operators (||, &&, !)

The function of logical operators is to join more than one condition or expression

and return either true or false as result. The table 4 given below lists all the logical

operators available in C++ and Java.

Operator Name Example with

X=20, Y=10 & Z=

30

Description

|| OR X>Z || X>Y will return

TRUE

Combines expressions and returns true if

one or all the expressions are true, otherwise returns false

&& AND X>Z && X>Y will return FALSE

Combines expressions and returns true if all the expressions are true, otherwise returns

false

! NOT !(X>Z && X>Y) will

return TRUE

It has only one operand located at its right.

It returns the opposite result of evaluating

its operand. It means that this operator inverts the value of its operand, producing

false if its operand is true and true if its

operand is false

Assignment Operator (=)

The assignment operator (=) is used to assign a value to a variable. This variable

may be of any type.

For example,

A = 110;

The above expression assigns integer value 110 to variable ‘A’.

The expression on the left of the assignment (=) operator is known as lvalue (left

value) and the one on the right is called rvalue (right value). lvalue must always be

a variable whereas rvalue is either a constant, a variable, the result of an operation

or any combination of them.

Note that the assignment operation always takes place from right to left and not

vice versa.

For example, in statement a=b; the value of variable b (rvalue) is assigned to

variable a (lvalue).

Standard Input/Output Streams in Java

Java programs also perform input-output operations through streams. InputStream

is used for input operation and OutputStream is used for output operations. Both

the streams are defined in java.io.package.

In order to make all the classes of a package available to a program available to a

program, the syntax is:

Import .*;

For example: import java.io;

The java.io package contains almost every class might ever need to perform an

input-output operation in Java programs.

System.out.println() displays messages and/or values of the variables and/or result

of an expression to the command window.

In this statement:

System is a class defined within the java.lang package.

out is a public static member of the System class.

println() is a method that accepts an expression as an argument and displays

it in String form to the standard output window.

You can also use System.out.print() in place of System.out.println(). The

difference between the two is as follows:

System.out.println() adds a new line to the end of the output. It places the cursor

on a new line.

Example:

System.out.println(“1”);

System.out.println(“2”);

System.out.println(“3”);

Output:

1

2

3

Example:

System.out.print(“1”);

System.out.print(“2”);

System.out.print(“3”);

Output:

123

Omitted Pages:-

57, 58, 59, 60, 61[Fig. 10 & Fig. 11],

68 [instance variables, class variables, local variable],

72 [From Standard Input/output Streams in C++], 73, 74 [Eg:9 & 10]

Textbook Exercise

Ex: A. Tick the correct option.

1. An identifier can denote ________.

a. Variable name

b. Class name

c. Function name

d. All of these

2. Which of the following statements is correct?

a. Identifiers can be made up of letters, digits and the underscore (_)

character.

b. Identifiers can use symbols such as ? or %.

c. Spaces are permitted inside identifiers.

d. Identifiers are not case sensitive.

3. Which operator is used to assign a value to a variable?

a. Arithmetic

b. Assignment

c. Relational

d. None of these

4. Which operator combines test conditions?

a. Compound operator

b. Equals operator

c. Complex operator

d. Logical operator

5. Omit

Ex: B. Fill in the blanks

1. The smallest individual unit in a program is known as ________.

2. Omit

3. A class is a group of objects that share similar ________ (attributes) and

behavior (methods).

4. Omit

5. Omit

Ex: C. Write True or False

1. Relational operators are used to combine two or more conditional

statements.

2. Keywords are not case sensitive and they can be typed in any case.

3. The java.io.package contains almost every class that you might need to

perform an input-output operation in Java programs.

4. In Java, System.out.println doesn’t adds a new line to the end of the output.

5. The assignment operation always takes place from left to right.

Ex: D. Match the columns.

Column A Column B

1 !(30 == 30) a True

4 int b False

5 30 != 50 c Data type

Ex: E Answer the following questions.

1. Name the main features of object-oriented programming.

2. Omit

3. Omit

4. Omit

5. How are variables declared and initialized in Java? Give syntax and

example of it.

Textbook Exercise Solution

Ex: A. Tick the correct option.

1. d: All of these

2. a: Identifiers can be made up of letters, digits, and the underscore (_)

character.

3. b: assignment

4. d: Logical operator

5. Omit

Ex: B. Fill in the blanks

1. Token

2. Omit

3. Characteristics

4. Omit

5. Omit

Ex: C. Write True or False

1. False

Correct Statement:

Logical operators are used to combine two or more conditional statements.

2. False

Correct Statement:

Keywords are case sensitive and they can be typed in any case.

3. True

4. False

Correct Statement:

In Java, System.out.println adds a new line to the end of the output.

5. False

Correct Statement:

The assignment operation always takes place from right to left.

Ex: D. Match the columns.

1- b

2-omit

3-omit

4-c

5-a

Ex: E Answer the following questions [Given during class]

Learn the following boxes from the textbook:-

Tech Terms [No. 8 Omit]

Recall Time [No. 4 omit]

Smart Byte [Pg. no. 67]

Table 1 [Pg. No. 67]

Table 2 [Pg. No. 70]

Table 3 [Pg. No. 70 & 71]

Table 4 [Pg. No. 71]

[Note: Values of Example in table 2, 3 & 4 can change]