Data Types
1. PDT (Primitive Data Type)
A type that contains the data itself
Primitive data types => Only 8!
The data is directly in the memory space
The
. (dot) operatorcannot be used => why? Because it's not an address!
1. Boolean type
boolean: 1bit
(true/false) -> JAVA does not allow 0 or 1
2. Character type
char: 2byte
ex) 'a' -> only a single character is possible
=> Uses single quotation('') -> stored as ASCII code value
+
byte == 8bit (1 byte) == -128 ~127
3. Integer type
Short: 16 bit (2 byte)
Int
: 32bit (4 byte) => The default for integer types is Int
Long: 64bit (8 byte)
4. Floating-point type
float: 32bit (4 byte)
Double: 64bit (8 byte) => The default for floating-point types is Double
-> Everything except the 8 types above is a Reference Type!!!!!
2. Reference Type
A type that contains an address
: Reference data type
The memory space contains an address, and you must follow the address to find the actual data
The
. (dot) operatorcan be used!! ex) address.In Reference types, you must use new for everything except String
String can be used like a primitive type or with new!!
New is placed in the Heap area
Using it like a primitive type places it in a different area than new => this consumes less data!
ex) String address = new String("Bitcamp"); -> when using new
String address = "Bitcamp"; -> when used like a primitive type
String is an immutable object!
-> So to change String data, you need to use StringBuilder or StringBuffer
Buffer
= A temporary memory space
null value
= A value that explicitly indicates the absence of an address in reference types
ex) now = null;
Java tries to match types based on the operator!
ex 1)
-> It matches the type to a floating-point type (1 becomes 1.0)
=> Since there is no data loss when converting from integer to floating-point, type promotion occurs automatically
ex 2)
-> Since the result is a string, the type is declared as String
=> The type changes depending on what the result value is!
char type & int type
char type automatically undergoes promotion to int type!
=> but, to convert int to char, type casting must be done
-> why? Because there is data loss!
: char 2 byte < int 4 byte
To go from a larger size to a smaller size, type casting is required because there is data loss!
(Summary)
Larger size -> Smaller size => Data loss exists => Type Casting
Smaller size -> Larger size => No data loss => Promotion
(Type Promotion in JAVA)
Last updated