Class 10 ICSE - Java

Values and Datatype

Character Set



First step in learning any languages knowing its character set

How do we have learn English language?
English language consist of a set of characters set which is comprised of :

(a) Alphabets ⇛ (A-Z) and (a-z)

(b) Digits ⇛ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

(c) Special characters ⇛ !, @, %, *, $, ^, etc.

So, character set is defined as a set of characters used in any language for forming words sentences paragraphs etc.

Similarly,
Java is also programming language it also has a set of characters used in forming tokens, instructions, programs etc.

Character Set in Java :

  • Alphabets : (A-Z) and (a-z)

  • Digits : 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

  • Special Characters : !, @, %, *, $, ^, etc.

  • Escape sequences : \n, \t, \b, \a, \v, \", \' etc.

Note : In Java programming language characters are defined using Unicode character set

ASCII Character Set



  • ASCII code stand for American standard code for information interchange

  • In ASCII format we use alphanumeric numbers

  • In this each character represented in 7 bits

  • It consists of total 128 characters.

Note : We cannot represent all characters using ASCII code

Let us see the example given below :


Output :


Unicode Character Set



  • It was developed by Unicode Consortium

  • It can represent all type of languages like Japanese, Hindi, French, English and German.

  • In this each character represented in 16 bits

  • It supports total of 65,000 characters

  • It can represent all types of characters.

Note :
⇛ Unicode is not efficient due to storage and transmission

⇛ Java program mostly uses ASCII code and Unicode for variable names, comments etc.

Let us see the example given below :


Output :



Tokens




A statement is composed of various components. Each smallest individual unit of a programming statement is known as Token.

The various types of tokens available in Java are :

⇛ literals

⇛ Identifiers

⇛ Keywords

⇛ Punctuators

⇛ Seperataors

⇛ Operators



Literals





Literal are the constants in Java program ,which remains fixed (i.e. do not change) during the execution of the program. Such quantities are termed as literals or constants

Java uses the literals classified in the following ways:


Integer Literals :

The numbers which are represented without decimal point are called Integer Literals. These are the whole numbers having positive or negative values.
Ex - 14, 345, 8, 6392, -18, -391 etc.

Real Literals :

These are also called floating-point constants. They represent number with decimal points.
Ex- 24.6. 0.0072. -3.652. 1.0E-03 etc.

Character Literals :

The constants, which are alphanumeric in nature, are called character literals. All alphabets upper or lower case, digits, special characters can be termed as character literals.
Ex - 'A', 'd', '3', '*' etc.
A character literal represents a single character enclosed within single quotes.

String Literals :

String is a set of alphanumeric characters. A group of characters enclosed within a pair of opening and closing double quotes is known as string literal. e.g., "CRISTOPHER ALEXANDER", "Coder", "teacher" etc.

Boolean Literals :

Boolean constants are special literals. They represent true or false and can be applied in a java program to ensure that a given logical condition is satisfied or not. You must note that Boolean constants (i.e. true or false) are never enclosed within quotes. This characteristic makes Boolean constants different than string constants.

Null Literals :

This is another special purpose literal. It is represented as '\0'. It is applied in a java program as a string terminator to mark end of the string.



Identifiers




Identifiers are names for a class, a method, a constant, or a variable. Some words in Java are reserved and cannot be used as identifiers. Certain rules must be followed in java while we are defining an identifier otherwise the compiler will throw an error.

It is recommended to follow these rules while defining an identifier :

  • An identifier can consist of any combination of letters, digits , the underscore character (_) and the dollar sign ($).

  • It cannot begin with a digit.

  • It may be of any length.

  • Both uppercase and lower case letters can be used in naming an identifier

  • Java is a case sensitive language which means that 2 identifier names that differ only in uppercase and lower case characters are considered to be different identifiers. Therefore, total, Total, ToTal and TOTAL are different identifiers

  • Can identify and cannot be a keyword or a boolean literal or a null literal

Examples of some valid identifiers :
student1, my_login_details, CheckPalindrome, $10_20, _details, SIMPLE_INTREST, SUM, customerDetails.



Keywords




Keywords, also known as reserved Words, are the words that convey a special meaning to the Java compiler. Java compiler reserves these keywords for its own use, and hence they cannot be used as names for variables or methods. Some of the Java keywords are listed below:

abstract assert boolean break byte
case catch char class const
continue default do double else
enum extends final finally float
for goto if implements import
instanceof int interface long native
new package private protected public
return short static strictfp super
switch synchronized this throw throws
transient try void volatile while


Punctuators




Punctuators are the punctuation signs used as special characters in Java. Some of the punctuators are ?(Question mark), ;(semi colon), .(Dot) etc.

Dot(.) is used to represent the scope of a function i.e. a function belonging to an object of a class.
Example : System.out.println(), java.io.* etc.

Semi colon(;) is used in a Java program as a statement terminator. It indicates the end of a statement. Any line continued after (;) is treated as the next line.
Example : int a = 5; System.out.println(a); are treated two separate statements in Java.


Seperators




They are the special characters in Java, which are used to separate the variables are the characters.
Example : Brackets (), Curly brackets {}, Square brackets [], etc.

Comma (,) In Java program is applied to separate multiple variables under same declaration.
Example : int a,b,c;

Brackets () are used to enclose any arithmetical or relational expression.

Curly brackets {} are applied to enclose a group of statement under compound statement.

Square brackets [] are used to include subscript or cell number of a dimensional array.


Operators




Operators are basically the symbols are tokens to perform arithmetical or logical operations to yield meaningful results. Basically there are 3 types of operators used in Java :

  • Arithmetical Operators : +, -, /, * etc.

  • Relational Operators : <, >, = =, !=, <= etc.

  • Logical Operators : &&, ||, ! etc.

Let us see some of the operators in the table given below :

Unary Operators +(unary) -(unary)
Assignment Operator =
Arithmetic Operators + - * / %
Relational Operators > < >= <= == !=
Increment/Decrement Operators ++ --
Logical Operators && || !
Bitwise Operators & | ^ ~ << >>
Conditional/Ternary Operator ?:


Escape Sequences




These are some special non graphic characters, which are used as commands to direct the cursor while printing. These characters are frequently used in Java programming called escape sequences. An escape sequence character begins with a backslash (\) and it is followed by one or more character. A table is given below with some escape sequence character


Escape Sequences Short Description
\t Horizontal tab
\v Vertical tab
\\ Backslash
\' Single quote
\" Double quote
\n New line
\b backspace
\f Formfeed
\0 Null
\r Carriage return


Datatype




As the name suggest,java allows programmer to use any type of data needed in the program.Whenever,we pass any value,we have to tell,what type of value we are using like integer type,decimal type or alphabets type.So for that purpose datatype is used.

Datatype is used to declare variables and each variable is necesssary to be declared to be used in the program.

Let us see example of this concept.


Here "x" is the variable that contains value as 10.And after x variable is int datatype that allow variable x to store integer value.This int datatype represent the type of data which is stored in x.

The datatype is broadly divided into two types,these are:
  • Primitive Datatype: This datatype include byte,short,int,long,char,float,
    double,and boolean
  • Non-Primitive Datatype: This datatype include classes,arrays and interfaces




Primitive Datatypes




Primitive datatypes are those datatypes which are predefined in programming languages,without these datatypes it is not possible to frame programs.They are the most basics datatypes in java languages.

There are 8 primitive datatypes boolean,char, byte, short, int, long, float and double .


Int Datatype in Java




This datatype is used to store integer type values.Its size is 32bits (4 bytes) and has a default value of 0.

The maximum and minimum value of integer it can store is -2 billon (-2^31) to +2 billion (2^31 -1) (approx.) .It can store numbers larger or smaller than the limits

Syntax:

int i=40;

The following table show size and range of int datatype.



Float Datatype in Java




This datatype is used to store decimal values.It size is 32 bits(4 bytes) and has a default value as 0.0f.

It is always recommended to use float in place of double datatype because it can store low precision value (upto 7 significant digits) while double store value with high precision values(upto 15 significant digits),so it can save memory in large arrays of floating-point numbers.

Syntax:

float b=43.4f;

The following table show size and range of float datatype.



Double Datatype in Java




This is similar to float datatype ,that is used to store decimal values.Its size is 64bits(8 bytes) and has a default value as 0.0d.

It is used to store high precision value,such as scientific readings,location of celestial bodies

Syntax:

double c=97.787d;

The following table show size and range of double datatype.



Char Datatype in Java




This datatype is used for storing single value character.Its size is 16 bits(2 bytes) and has default value as '\u0000',this is unicode format which java uses in place of ASCII.

These datatypes are enclosed with single quotes,for example 'k','q'.These characters group together and form a string,example "java","code".
Syntax:

char c='h';

The following table show size and range of char datatype.



Short Datatype in Java




It is similar to int datatype,and is used to save memory in large arrays.its size is 16 bits (2 bytes) and has a default value as 0.

Syntax:

short x=11;

The following table show size and range of short datatype.



Long Datatype in Java




It is similar to int datatype,and is used to huge sized numeric value .its size is 64 bits (8 bytes) and has a default value as 0.
It is useful where int type is not large enough to store the desired value
Syntax:

long x=93219898L;

The following table show size and range of long datatype.



Byte Datatype in Java




This datatype is used to store numeric values,it can be used as a replacement for int datatype as it is useful for saving memory in large arrays,it doesn't have the size range as the integer datatype.
Its size is 8bits(1 byte) and has default value as 0.
Syntax:

byte x=8;

The following table show size and range of byte datatype.



Boolean Datatype in Java




This datatype have only 2 values which are 'true' and 'false',these represent logical value.Its size is only 8bits(1 byte) that is either true or false.It has a default value as 'false'.
Syntax:

boolean check=true;

The following table show size and range of boolean datatype.



Non-Primitive Datatype




Non-Primitive datatype are also called user-defined datatype.They are created by programmers and can be assigned as null.




Object




It is defined as a real life entity,whatever we see in real life is termed as an object.These entities have some properties and task to perform.It is a basic unit of object-Oriented Programming language.



An object is also said to be an instance of class,that is ,it will follow all the prototype defined by the class.There can be mutliple instance of a class in a program.

An object consists of:-

  1. unique Identity:Each object has unique Identity,that enable object to interact with other objects
  2. Behavior: It tells what object does.It can be used a response for one object to other objects
  3. State/Properties/Attributes: It tells how the object will look like.


Class




  • A Java class is a structure from which an object can be instantiated and it can have various methods and class attributes. A class determines the data fields and actions of an object.

  • In Java class variables are used to define the data fields and methods to define the actions.

  • It is also known as blueprint of prototype of an object

  • Classes are divided in two categories :
    • Pre-defined Classes : Pre-defined classes are those classes that already exists in Java, such as Scanner, System, String etc
    • User-defined Classes : User-defined classes are created by you the programmer / user. These classes take on names that you assign to them and perform tasks that you create . Such as Dog , Test, Demo etc





Strings




In java string is a class ,which has lot of different methods performed on string like valueOf(),replace(),length(),etc.To access these methods we create instance of this class.


This String class is available in java.lang package and to use this package we write

import java.lang.*;

This package is the default package ,so we dont need to explicitly write in the program,it is imported in the java program by default.

These String objects are immutable(cannot modified on same location).That is when we modify this class object as:

str="World" .

Then new instance will be created,the more the number of times the user will modify this object ,the more new instance will be created and consume the heap memory.

It is also a non-primitive datatype,having sequence of characters or we can say array of characters that is enclosed in a double quotes.



Variables




Variables are defined as the name of memory location that contain a data value.It also said to be user-defined name ,which is given by the user.

As soon as the variable is declared the memory will be allocated to the data value and can be used in java program.

Variable can store any type of value,but for that we have to mention datatype before creating the variable,like:

int x=12;
String a="ch";
char d='a';
double a=19.87;


Let us understand this concept by the example:-


In the above diagram to store or access this data value,we have to add a user-defined name,so that we can call that data value by the name defined,for these purpose we use variables along with datatype.


We can change value of variable also during program execution.

a=a+40;

Now the value in memory location for variable a will change to 60(20+40).

Constants



A constant is a variable whose value cannot be changed during the execution of program.

Syntax :

final float pi = 3.14f;

To define a variable as a constant, we just need to add the keyword “final" as shown in above syntax.

Let us understand it with a example given below :



Output :



There are various advantages of using constants in our code :

(i) It increases the readbility of the program and make it easier for the user to understand the code.

(ii) Any unintentional changes to such variables is flagged by compiler.

(iii) If you want to make changes to such variables then we have to modify its value at one place and all other occurrences will be done automatically.


Comments



Comments in Java are non-executable statements that are ignored by the compiler and interpreter. It can be used to increase the readbility of the code by providing information or explanation about the variable, method, class or any statement.

Basically, there are three types of comments in Java. They are as follows:

  • Single-line comments

  • Multi-line comments

  • Documentation comments

Single-line Comment :

A single-line comment starts and ends in the same line. To write a single-line comment, we can use the // symbol.

Syntax :

    // This is a single line comment

Example :

                
class Main {
    public static void main(String[] args) {    	
        // prints "Hello, World!"
        System.out.println("Hello, World!");
    }
}
                    
                


Multi-line Comment :

When we want to write comments in multiple lines, we can use the multi-line comment. To write multi-line comments, it should start with '/*' and ends with '*/' symbol.

Syntax :

/* This is a 
multiline comment
.
.
.
Comment ends*/

Example :

                                   
class HelloWorld 
{
/* This is an example of  multi-line comment.
* The program prints "Hello, World!" to the standard output.
*/
    public static void main(String[] args) 
    {

        System.out.println("Hello, World!");
    }
}
                


Documentation Comment :

This type of comments is used generally when you are writing code for a project/ software package. It helps you to generate a documentation page for reference, which can be used for getting information about methods present, its parameters, etc.

Syntax :

    /** this is a documentation
    comment
    
    
    comment ends*/

Contact Us

REACH US

SERVICES

  • CODING
  • ON-LINE PREPARATION
  • JAVA & PYTHON

ADDRESS

B-54, Krishna Bhawan, Parag Narain Road, Near Butler Palace Colony Lucknow
Contact:+ 919839520987
Email:info@alexsir.com