Variables and data types in Java

Variable is a memory location which stores data. In Java, we have to define what type of variable (integer, text, string, etc.), we are storing. After it a fixed memory is assign to each variable. For example, normal integer is assign 4 bytes. We can not assign other type of values to defined variables. For example, if we have defined a variable as integer then we can not assign a text string to that variable. We can modify that variable with different value of same type (say another integer). In java, there are 8 types of primitive variables.

1. Integer
2. Byte
3. Char
4. Boolean
5. Double
6. short
7. long
8. float

NOTE:

1. Run below examples by writing in main method. To print them in console use System.print.out("variable");
2. We can give variables any name other than reserved keywords starting with letter, $ or underscore (_).

Integer:

Integer is a 32-bit data type which stores integer values from range - 2,147,483,648 ( -2^31 ) to 2,147,483,647(inclusive) ( 2^31 -1 ).

Example:

int a = 8;
a = 10;

Byte:

It is 8-bit data type used to store integer value from -128 to 127 (inclusive).

Example:

byte a = 23;
a = -24;

Char:

It is 16-bit unicode character which stores any character.

Example:

char a = 'a';
a = 'z';

NOTE: Character is written inside single colons '' but string is written in double colons "".

Boolean:

It is one bit boolean data type which has only two values: true or false.
Example:

boolean a = true;
a = false;

Double:

Double data type is a double-precision 64-bit IEEE 754 floating point. This should not be used for precise values such as currency.
Example:

double a = 56; 
a = 45.98;

Short:

Short data type is a 16-bit signed two's complement integer. Its range is from -32,768 to 32,767 (inclusive).

Long:

Long data type is a 64-bit signed two's complement integer. Its range is -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 (inclusive). It is used when we need wider range for integers.
Example:

int a = 200000L;
a = -300000L;

Float:

Float data type is a single-precision 32-bit IEEE 754 floating point. Float data type is also never used for precise values such as currency.

More types:

String:

String is an array of characters. We will read about array in detail later. At this moment you may assume string is a collection of characters. It is simple text.