Transcript The character data type char

The character data type char
Character type char
• The char data type:
• is a built-in (primitive) data type of Java
• is used to represent alpha-numerical information (characters)
inside the computer
• uses the Unicode to encode characters from many different
kinds of languages in the world
• uses 2 bytes of memory to store the Unicode value
• The Unicode includes the ASCII code which is used to
encode English characters
Character type char (cont.)
• Unicode:
• Official website for Unicode: click here
• Unicode provides a unique number for every character
Example:
• The number 65 of Unicode represents the (English) character A
• The number 35 of Unicode represents the character #
• The number 948 of Unicode represents the (Greek) character δ
• The number 24373 of Unicode represents the (Chinese)
character 張
Character type char (cont.)
• ASCII code:
• The value 0 --- 127 of the Unicode is called the ASCII
code
• The American Standard Code for Information Interchange
(ASCII) code was designed to represent characters in the
English alphabet
Character type char (cont.)
• ASCII code: (with letters and number highlighted)
0 NUL 1 SOH 2 STX 3 ETX 4 EOT 5 ENQ 6 ACK 7 BEL
8 BS 9 HT 10 NL 11 VT 12 NP 13 CR 14 SO 15 SI
16 DLE 17 DC1 18 DC2 19 DC3 20 DC4 21 NAK 22 SYN 23 ETB
24 CAN 25 EM 26 SUB 27 ESC 28 FS 29 GS 30 RS 31 US
32 SP 33 ! 34 " 35 # 36 $ 37 % 38 & 39 '
40 ( 41 ) 42 * 43 + 44 , 45 - 46 . 47 /
48 0 49 1 50 2 51 3 52 4 53 5 54 6 55 7
56 8 57 9 58 : 59 ; 60 < 61 = 62 > 63 ?
64 @ 65 A 66 B 67 C 68 D 69 E 70 F 71 G
72 H 73 I 74 J 75 K 76 L 77 M 78 N 79 O
80 P 81 Q 82 R 83 S 84 T 85 U 86 V 87 W
88 X 89 Y 90 Z 91 [ 92 \ 93 ] 94 ^ 95 _
96 ` 97 a 98 b 99 c 100 d 101 e 102 f 103 g
104 h 105 i 106 j 107 k 108 l 109 m 110 n 111 o
112 p 113 q 114 r 115 s 116 t 117 u 118 v 119 w
120 x 121 y 122 z 123 { 124 | 125 } 126 ~ 127 DEL
Character type char (cont.)
• Here is an ASCII code table in hexadecimal, decimal and
binary numbers
Character literals
• We write numerical literals as follows:
123
3.1415
(And so on)
Character literals (cont.)
• We cannot write character literals as follows:
A
a
(And so on)
because:
• They can be confused with identifiers !!!
(E.g., names of variables)
Character literals (cont.)
• Character literals:
• A character literal is written between quotes '...'
• Examples:
• 'A' is the character literal A (ASCII code value 65)
• 'a' is the character literal a (ASCII code value 97)
• '1' is the character literal 1 (ASCII code value 49)
Defining character typed variables
• Syntax to define an character typed variable:
char NameOfVariable
;
Notes:
• The keyword char announces the variable definition clause
• The NameOfVariable is an identifier which is the name of the
variable.
• The variable definition clause is must be ended with a semicolon ";"
• A char typed variable can store the Unicode of one character
Defining character typed variables (cont.)
• Example:
public class Char01
{
public static void main(String[] args)
{
char a;
a = 'b';
// a = ASCII code of 'b' (98)
System.out.println(a); // Print a using ASCII code
}
}
Defining character typed variables (cont.)
• Example Program: (Demo above code)
– Prog file:
http://mathcs.emory.edu/~cheung/Courses/170/Syllabus/05/Progs/
Char01.java
• How to run the program:
• Right click on link and save in a scratch directory
• To compile: javac Char01.java
• To run:
java Char01
Operations on the char data type
• No arithmetic operations:
• We do not add, subtract, multiply or divide one character
with another character...
• There are no arithmetic operations defined on the char
data type
The only available operations are ++ and --.
Operations on the char data type (cont.)
• The ++ and -- operations applied on char typed variables:
• The ++ operation applied on a char typed variable will
increment the (Unicode) value
The variable will contain the (Unicode) value of the next
character
• The -- operation applied on a char typed variable will
increment the (Unicode) value
The variable will contain the (Unicode) value of the
previous character
Operations on the char data type (cont.)
• Example:
public class Char02
{
public static void main(String[] args)
{
char a;
a = 'b';
System.out.println(a); // Prints b
a++;
// "Next" character
System.out.println(a); // Prints c
}
}
Operations on the char data type (cont.)
• Explanation:
• The variable a first contains the Unicode for the character 'b'
which is equal to 98:
..... (portion of the ASCII code table) ....
88 X 89 Y 90 Z 91 [ 92 \ 93 ] 94 ^ 95 _
96 ` 97 a 98 b 99 c 100 d 101 e 102 f 103 g
104 h 105 i 106 j 107 k 108 l 109 m 110 n 111 o
.....
• The statement a++; increments the variable a to the new
value 99 which is the code for the character 'c'
• That's why when variable a is printed, the letter 'c' is printed.
Operations on the char data type (cont.)
• Example Program: (Demo above code)
– Prog file:
http://mathcs.emory.edu/~cheung/Courses/170/Syllabus/05/Progs/
Char02.java
• How to run the program:
• Right click on link and save in a scratch directory
• To compile: javac Char02.java
• To run:
java Char02
Exercise
• What will the following program print:
public class Char02a
{
public static void main(String[] args)
{
char a;
a = '%';
System.out.println(a); // Prints %
a++;
// "Next" character
System.out.println(a); // What will this statement print ?
}
}
Exercise (cont.)
• Hint: use the ASCII table
Exercise (cont.)
• Answer: &
Converting a number type into char
• Java allows you to convert a numerically typed (integer,
short, etc) into the char type.
Converting a number type into char (cont.)
• Example:
public class Char03
{
public static void main(String[] args)
{
int x;
char a;
x = 98;
// a = x;
a = (char) x;
// 98 is the code for 'b'
// This is not allowed without casting
// Convert int to char
System.out.println(a); // Prints b
}
}
Converting a number type into char (cont.)
• Explanation:
• The variable x is assigned the value 98 (which is the
Unicode for the character 'b'):
(The bit pattern 00000000 00000000 00000000 01100010
encodes 98 using the binary number system
Converting a number type into char (cont.)
• The statement a = (char) x; will achieve the following:
This statement copies the value from an int typed variable
into a char typed variable.
Converting a number type into char (cont.)
• Effect:
• The (same) value will now be interpreted using
the Unicode code
(E.g.: The pattern 00000000 01100010 is equal to
98 and according to the Unicode scheme, it is the
code for the letter 'b')
• That's why System.out.println(a); will print the letter 'b'.
Converting a number type into char (cont.)
• Example Program: (Demo above code)
– Prog file:
http://mathcs.emory.edu/~cheung/Courses/170/Syllabus/05/Progs/
Char03.java
• How to run the program:
• Right click on link and save in a scratch directory
• To compile: javac Char03.java
• To run:
java Char03
Converting a char typed value into an integer
• We can also do the reverse:
• Convert a char typed value into an integer
Converting a char typed value into an
integer (cont.)
• Example:
public class Char04
{
public static void main(String[] args)
{
int x;
char a;
a = '%';
// ASCII code of '%' = 37
x = a;
// Copy 37 into x
// We don't need to use (int)
// is is "safe" (int is bigger than char)
System.out.println(x); // Prints 37
}
}
Converting a char typed value into an
integer (cont.)
• Explanation:
• The variable a is assigned the Unicode value for the
character % (which is the number 37):
(The bit pattern 00000000 00100101 encodes the number
37 and it is the Unicode for the character '%'
Converting a char typed value into an
integer (cont.)
• The statement x = a; will achieve the following:
This statement copies the value from a char typed variable
into a int typed variable.
Converting a char typed value into an
integer (cont.)
• Effect:
• The (same) value will now be interpreted using
the binary number system
(E.g.: The pattern 00000000 00000000 00000000
00100101 is equal to 37
• That's why System.out.println(x); will print the number 37.
Converting a char typed value into an
integer (cont.)
• Example Program: (Demo above code)
– Prog file:
http://mathcs.emory.edu/~cheung/Courses/170/Syllabus/05/Progs/
Char04.java
• How to run the program:
• Right click on link and save in a scratch directory
• To compile: javac Char04.java
• To run:
java Char04