Characters and Unicode - PowerPoint Presentation

Slide1

Characters and Unicode

Java Data TypesSlide2

Unicode

Characters, like the letters of the alphabet and other printable symbols, are represented internally in the computer by a numerical code.

The coding system that Java relies on for characters is called Unicode.

Unicode assigns an integer value to each separate printable character.

Unicode is based in part on a previous coding system known as ASCII.Slide3

Unicode

Though Unicode handles thousands of characters, this will only cover the first 128 codes.

English alphabet

Keyboard symbols

Codes that don’t represent printable charactersSlide4

Control codes

The first 32 codes are non-printable control codes.

They are referred to as control codes because they originated as instructions for communicating with or controlling a device.

Most of these codes are of no use to the programmer.

But there are some, such as the line feed and carriage return codes, which may be useful for printed output.Slide5

Control codes

System.out.print

(“\n”);

The escape sequence “\n” causes the pair of control codes, line feed and carriage return, to be generated. Similarly, “\t” causes a horizontal tab to be generated.

Although not literally printable, these characters can affect the appearance of the output.Slide6

Control codes

Code

Name

Description

16

DLE

Data link escape

17

DC1

Device control 1

18

DC2Device control 219DC3Device control 320DC4Device control 421NAKNegative acknowledge22SYNSynchronous idle23ETBEnd of transm. Block24CANCancel25EMEnd of medium26SUBSubstitute27ESCEscape28FSFile separator29GSGroup separator30RSRecord separator31USUnit separator

Code

Name

Description

0

NUL

Null

1

SOH

Start of Heading

2

STX

Start of text

3

ETX

End of text

4

EOT

End of transmission

5

ENQ

Enquiry

6

ACK

Acknowledge

7

BEL

Bell

8

BS

Backspace

9

HT

Horizontal tab

10

LF

Line feed

11

VT

Vertical tab

12

FF

Form feed

13

CR

Carriage return

14

SO

Shift out

15

SI

Shift inSlide7

Unicode characters

The Unicode values from 32 to 127 are printable, except for code 127, which stands for deletion.

The letters of the alphabet, small and capital, and the various punctuation marks are arranged as they are for historical reasons.

The sort order for characters or text items is based on their Unicode values.Slide8

Unicode charactersSlide9

New data type: char

We can now consider the character type, char.

‘char’ is effectively an integer type.

It is possible to cast between something typed char and something typed int.

The underlying value is always an integer.

The type (

int

or char) determines whether the integer value or the associated Unicode character is displayed.

The following program illustrates the idea that an integer can be cast to a character and printed out as such.Slide10

Char

public class

UnicodeChars

{

public static void main(String[]

args

)

{

char

myChar

;

int i; i = 65; myChar = (char) i; System.out.println(myChar); //Prints A }}Slide11

Char

In this program, the char type takes the integer value of 65, and finds the character associated with it, capital letter A.

It isn’t always necessary to use a number to assign a value to a char type. You can directly set the character you want.

myChar

= ‘A’;

Note that we use single quotes instead of double quotes to denote a single character value.

Double quotes signify a string, while single quotes signify a character

.Slide12

Finding the integer value of a char

It is also possible to find the integer value of a char type, by casting it to an

int

, as shown below:

Char

myChar

= ‘A’;

int

i = (

int

)

myChar;System.out.println(i); //Prints 65Slide13

Lab

Prepare yourselves! You are now ready for questions 39 to 42 on the assignment sheet.

The first couple of questions consists of determining a character from an integer, and an integer from a character.

The last couple will involve taking an integer/char type, and turning it into the

other type.