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

Unicode:

Official website for Unicode: click here
Here is a Unicode chart: 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

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

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

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)

We cannot write character literals as follows:
because:

Character literals:

A character literal is written between quotes '...'

Examples:

'A' is the character literal A (Unicode code value 65)
'a' is the character literal a (Unicode code value 97)
'1' is the character literal 1 (Unicode code value 49)

I just want to very sure that you realize that:

A char variable is an integer typed variable.
The expression 'A' is an integer (= 65) in a Java program !!!!

Try running this program:

public class Char01B { public static void main(String[] args) { char a; a = 65; // 65 = Char code for the character 'A' System.out.println(a); // Prints 'A' !!! int i; i = 'A' + 1; // 'A' is just an integer !!! System.out.println(i); // Prints 66 !!! } }

Example Program: (Demo above code)
- Prog file: click here

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 semi-colon ";"
A char typed variable can store the Unicode of one character

Example:

public class Char01 { public static void main(String[] args) { char a; a = 'b'; // a = ASCII code of 'b' (98) System.out.println(a); // Prints the character b !!! } }

Example Program: (Demo above code)
- Prog file: click here
How to run the program:

Important differenc in printing character variables and integer variables

Although char type is a kind of integer type, it is treated differently when we want to "see" the value (e.g., printing)
The print and println methods in System.out can tell the difference between:

Different encoding methods used in printing:

When printing a char typed integer, the print and println methods will use the Unicode table to print the corresponding character.
When printing other kinds of integer types, the print and println methods will use the binary number encoding.
(I.e.: 00000001 is 1, 00000010 is 2, and so on)

Summary on variable of the type char

Summary on a char typed variable

A char type variable consists of 2 bytes
It contains the Unicode code of some character
A char type variable is an integer type variable that contains a positive number

Converting char to int: Operations on the char data type

Character code is number:

A char typed variable contains a character code
A character code is a (positive) number
Recall that:
Recall that: the conversion from char to int is safe:

Example:

public class Char01A { public static void main(String[] args) { char a, b; int i; a = 'x'; i = a; // Safe conversion System.out.println(i); // Prints 120 (ASCII code for 'x') a = 'x'; i = a+1; System.out.println(i); // Prints 121 a = 'x'; b = 'y'; i = a + b; System.out.println(i); // Prints 241 (ASCII code for 'y' = 121) } }

Explanation:

The variable a contains the Unicode for the character 'x' which is equal to 120:

..... (portion of the ASCII code table) .... 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

The expression a + 1; computes 120 + 1 because the ASCII code for the character 'x' is 120

Example Program: (Demo above code)
- Prog file: click here
How to run the program:

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 ? } }

Hint: use the ASCII table

Answer: &
Example Program: (Demo above code)
- Prog file: click here
How to run the program:

Converting other integer type into char

The range of byte, short, int, and long include some negative values
The range of values of char only contain positive values (including 0).
Therefore:
Recall the following list of unsafe conversions that was discussed previously:
Therefore:

Example:

public class Char03 { public static void main(String[] args) { int x; char a; x = 98; // 98 is the code for 'b' // a = x; // This is not allowed without casting a = (char) x; // Convert int to char System.out.println(a); // Prints b } }

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

The statement a = (char) x; will achieve the following:

This statement copies the value from an int typed variable into a char typed variable.

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 thw Unicode scheme, it is the code for the letter 'b')

That's why System.out.println(a); will print the letter 'b'.

Example Program: (Demo above code)
- Prog file: click here
How to run the program:

Testing for lower case characters

Consider the ASCII code table:

How to detect a lower case letter:

When the ASCII code of the character is

Testing for upper case characters

Consider the ASCII code table:

How to detect an upper case letter:

When the ASCII code of the character is

Converting a lower case character into the same upper case character

Consider the ASCII code table:

How to convert a lower case character code to the same character in upper case:

'a' ⇒ 'A' means: 97 ⇒ 65 (97 - 32 = 65) 'b' ⇒ 'B' means: 98 ⇒ 66 (98 - 32 = 66) 'c' ⇒ 'C' means: 99 ⇒ 67 (99 - 32 = 67) And so on...

Lower case to upper case conversion algorithm:

We can convert an Unicode code for a lower case letter into the same upper case letter by subtracting 32 from the code value.

Example converting lower case to upper case:

public class Char05 { public static void main(String[] args) { char x; char y; x = 'a'; y = (char) (x - 32); // We need to cast, because (x - 32) is an int value ! System.out.println("x = '" + x + "', y = '" + y + "'"); x = 'b'; y = (char) (x - 32); System.out.println("x = '" + x + "', y = '" + y + "'"); x = 'c'; y = (char) (x - 32); System.out.println("x = '" + x + "', y = '" + y + "'"); } }

Example Program: (Demo above code)
- Prog file: click here
How to run the program:

The common way to convert lower case to upper case

We do not write out the constant 32

Instead, we use this little trick:

Unicode of 'A' = 65 Unicode of 'a' = 96 'a' - 'A' = 96 - 65 = 32 !!!

A better way to convert lower case to upper case:

public class Char05a { public static void main(String[] args) { char x; char y; x = 'a'; y = (char) (x - 'a' + 'A'); System.out.println("x = '" + x + "', y = '" + y + "'"); x = 'b'; y = (char) (x - 'a' + 'A'); System.out.println("x = '" + x + "', y = '" + y + "'"); x = 'c'; y = (char) (x - 'a' + 'A'); System.out.println("x = '" + x + "', y = '" + y + "'"); } }

Example Program: (Demo above code)
- Prog file: click here
How to run the program:

Converting upper case to lower case

We add 32 to the Unicode

The algorithm is:

char x; char y; x contains the Unicode of an upper case character y = (char) (x - 'A' + 'a'); // y = Unicode of the same lower case character

The character data type char

The character data type `char`