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Variables

Rules for creating variables

A variable may consist of one or more than one letters, numerals and underscore.
The first letter of the variable name shouldn’t be any numeral. It can be an alphabet or an underscore.
Try not to use meaningful variable names.
No reserved of Java should be used.
No blank spaces are allowed in a variable.
Java is case sensitive.

Data Types:

A programmer, while programming has to deal with various types of data. Hence, it becomes necessary that the programming language facilitates the programmer with all data types. Java provides all these.

Integers:

These are whole numbers suck as 2, 4, 6, -7, -9 etc. no fractional part is an integer. Integers are divided into four categories.

Byte – is that integer which has a very small value ranging from -128 to 127 bytes, i.e.8 bits.
Integer – are those positive or negative digits whose values vary from -2147483648 to 2147483648 If we have to use the value of 32770, we have to use an integer because the max of a short integer is 32767.
Short Integer – are those integers which have a short range of value-128 to 127 or 2¹⁵ to 2¹⁵-1.
Long Integers – are those that have a wide range of value ranging from -9223372036854775807 to 9223372036854775808 or -2⁶⁴ to 2⁶⁴-1.

Data Type	Size Bits	Range
Byte	8 Bits	-128 to 127
Integer	32 Bits	2147483648 to 2147483648
Short Integer	16 Bits	2¹⁵ to 2¹⁵-1
Long Integer	64 Bits	9223372036854775807 to 9223372036854775808 -2⁶⁴ to 2⁶⁴-1

Character Types

Character types are 2 bytes in size but can hold single characters. A character constant varies from 0 to 255. The characters are stored in the computer memory as integers in their binary form. Each character is assigned a particular value according to ASCII codes.

Character Type	Size	Rank
char	2byte	-256 to 255

Example of a Valid Character

char reply = y

char ans = a

String is a series of characters. These characters may be alphabets, digits, blank spaces etc. the string is enclosed within double quotes. The string is used to write or store messages.

Example:

“Hello”

“Hello” is a string and the characters of a string are stored in sequential locations.

String Variables:

String name;

String vh1;

String Address;

Floating point:

Float data type: a fractional number is a floating point number. Decimal in a number refers that it is a floating number. Floating points are divided into two parts:

float
double

Example:

Constants are fixed values that do not change during the execution of the program. Constants are also called literals. There are numeric and character constants. Numeric constants are divided into Integer constants float. Character constants are divided into character and string.

These are used for mathematical calculations. The result of an arithmetical expression is a numerical value. An arithmetical expression may be a variable or a constant or a combination of both. These variables or functions are connected with arithmetical operators.

These are used to determine the relationship between different operands. These are used in the work of comparison also; these are two mathematical expressions and are connected by relational operators. The relational expression returns 0 if the relation is false and returns 1 if the relation is true. The six relational operators are shown in the following table:

Logical operators combine the result of two or more than two expressions. They are made of connecting relationships in the expression refers as logic and the expressions are called logical expressions. The logical operator returns 0 if the relation is false and 1 if its true.

Java provided ++ and – which are not provided my many other languages. These operators are called increment and decrement operators. The increment operator adds 1 to the operand and decrement operator subtracts 1 from the operand.