Data Types

The data type of a variable represents the type of that variable. It decides the range and memory required by that variable.

The type of variables and expressions is known to the compiler and the assignments are checked by the compiler for type compatibility. Hence, java is a statically typed language.

There are two types of variables in java:

• Primitive-type
• Reference-type

Primitive Data Types:

These are the basic types. There are total eight primitive data types:

Data Type	Size(bytes)	Default Value
byte	1	0
short	2	0
int	4	0
long	8	0
float	4	0.0
double	8	0.0
char	2	‘ ‘(space)
boolean	Decided by jvm	False

Some important points:

• Old languages like C/C++ are ASCII code based and the the no. of different allowed ASCII code characters are less than or equal to 256. Hence, to represent these 256 characters 8-bits are enough (2^8=256). Hence, the size of char in old languages is 1 byte.
• But java is Unicode based and the number of different Unicode characters are more than 256 but less than or equal to 65536. Hence, it requires 2 bytes or 16 bits.
• Char array is preferred over String because String is immutable and the object is destroyed only when garbage collector clears it from the String pool otherwise it remains in the pool whereas in case of char array we can explicitly wipe the data after we are done with it or even overwrite the data.