Difference between revisions of "Misc"
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* Integers are stored in 2 complements's notation | * Integers are stored in 2 complements's notation | ||
* Leftmost bit is the sign bit, the remaining bits are used to store the value | * Leftmost bit is the sign bit, the remaining bits are used to store the value | ||
+ | e.g. of Byte | ||
* Byte - 1 byte = 8 bits. | * Byte - 1 byte = 8 bits. | ||
* Leftmost bit is to store the sign. So 7 bits are available for the value, so 2^7 = 128 values | * Leftmost bit is to store the sign. So 7 bits are available for the value, so 2^7 = 128 values | ||
Line 43: | Line 44: | ||
* Positive range is 0 to 127 (128 numbers, 0 is stored as a positive number) | * Positive range is 0 to 127 (128 numbers, 0 is stored as a positive number) | ||
* So a byte's range is -2^7 to (2^7 - 1) | * So a byte's range is -2^7 to (2^7 - 1) | ||
+ | |||
+ | * char's take up 2 bytes | ||
+ | * they are stored as '''unsigned''' 16-bit integers. This means they will represent a total of 2^16 positive values (0 to 65535 (2^16-1) ) | ||
+ | * contrast with short which also uses 2 bytes. But it's max positive range is 2^15 -1. (Since 1 bit is to used to represent the sign) | ||
<u> Comments </u> | <u> Comments </u> |
Revision as of 00:43, 21 June 2011
This covers Objective 1.3
Legal Identifiers
- Can be composed of characters, numbers, currency-symbols and connecting chars such as underscore.
- Definition of characters are interpreted according to the charset.
- NO special chars such as #, :, ;, @, -, etc...
- Must start with letter, currency char, underscore but CANNOT start with a digit !
- Java identifiers are case-sensitive.
Illegal identifiers:
- int 23age;
- String em@iladd;
- List all-accounts;
These are legal!:
- int __;
- String $;
Literals
- Default type of an integer literal is int.
- Long can be specified by adding l or L
- Octal prefix with 0
- Hex prefix with 0x or 0X
- Floating point literals default type is double.
float pi = 3.14; // This will be a compiler error, because 3.14 is a fp literal which is double by default
double pi = 3.14; //OK
float pi = 3.14f; //OK
- Double can also be explicitly by adding the suffix d or D
- Float is denoted by suffix f or F
- Integers are stored in 2 complements's notation
- Leftmost bit is the sign bit, the remaining bits are used to store the value
e.g. of Byte
- Byte - 1 byte = 8 bits.
- Leftmost bit is to store the sign. So 7 bits are available for the value, so 2^7 = 128 values
- Negative range is -128 to -1 (128 numbers)
- Positive range is 0 to 127 (128 numbers, 0 is stored as a positive number)
- So a byte's range is -2^7 to (2^7 - 1)
- char's take up 2 bytes
- they are stored as unsigned 16-bit integers. This means they will represent a total of 2^16 positive values (0 to 65535 (2^16-1) )
- contrast with short which also uses 2 bytes. But it's max positive range is 2^15 -1. (Since 1 bit is to used to represent the sign)
Comments
- Comment start sequences like //, /*. /** are ignored within comment blocks.
- So trying to nest multiple-line comments will result in an error
/* This is the foo algorithm
/* which takes foo's and sort's bars */
*/