JAVA FUNDAMENTALS
IDENTIFIERS:
In simple word identifier can be said to a name of a class, method, variable or label.it is mainly used for identification purpose.
For example:
class exmp{
Public void static main( String[ ] args ){
int x=10;
}
}
In above identifiers are
• Test
• Main
• String
• args
• x
Rules for defining identifiers:
• Characters which are allowed are alphanumeric ([A-Z] [a-z] [0-9]) and symbols $ and _ are allowed.
• Identifiers should not start with any digit [0-9].
• Identifiers are case-sensitive.
• No length limit for the identifier.
• Reserved words cannot be used as an identifier in java.
RESERVED WORDS:
Reserved words are used to represent certain functionalities defined by that language.
These can be divided into two parts.
• Keywords
• Reserved literals
DATA TYPES:
• Numeric data type: it is used to represent numbers.it can be divide into two type:-
1. Integral types
2. Floating types
1.Integral type: it is used to represent whole no.it can be categorized into four types:
• byte
• short
• int
• long
byte:
Size: 8 bits
Range: -128 …. 127
The most significant bit is called sign bit.0 means +ve 1 means –ve value.
+ve numbers represented directly into the memory whereas –ve numbers are represented in 2’s complement form.
For example:
byte b=100;
short:
Size: 16 bits
Range:-215 to 215[-32768 to 32767]
The most rarely used data type in java is short.
For example:
short s=-32768;
int:
Size: 32 bits
Range: -231 to 231
The most commonly used data type is int.
In java size of int is 4byte irrespective of any platform.
long:
Size: 64 bits
Range: -263 to 263
Whenever int is not enough to hold big value then we use long.
2.Floating type: used to represent real numbers.
It can be categorized into two types:
1. float
2. double
float:
Size:4 bytes
Range:-3.4e38 to 3.4e38
float follows single precision and if we want 5 to 6 decimal accuracy the we should go for float.
double:
Size:8 bytes
Range:-1.7e308 to 1.7e308
double follows double precision and if we want 14 to 15 decimal accuracy then we should go for double.
• Boolean data type: it is a type whose value is either true or false
Size: 1 bit
Range: not applicable
• Char data type: the character type whose values are 16 bit Unicode characters.
Size: 4 bytes
Range:0 to 65535
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