Java's built-in data types called primitive data types. The primitive data types are int, byte, short, long, float, double, char, and boolean. A variable of any of these data types is called a primitive variable. We explain primitive data types in more detail as follows:
Integers: An integer is a number that can be written without using a decimal point or a fraction. Examples of integers are numbers such as 23, -51, and 200. Integers can be represented using these primitive data types: int, byte, short, and long.
Floating-point numbers: Numbers such as 3.2 and 5.41 that contain a decimal point are floating-point numbers, not integers. Just as there are different data types for integer numbers, there are two types for floating-point numbers: float and double.
Characters: A character is a single letter of the alphabet, such as "A;' a digit, such as "1;' or a symbol, such as "%”. The char data type is used to hold a character.
True/false values: The Boolean type is different from all of the others because it does not hold a number or a character. Instead, it represents one of two values: true or false.
You might be wondering why multiple types such as byte, short, int, and long are used for integers, and float and double are used for floating-point numbers. The difference between them lies in the size of data they can hold.
For bytes, the numbers must lie within the range -128 to 127. This requires only 8 bits of memory. The short data type is used for integers that lie in the range -32,768 to 32,767, and it takes up 16 bits of memory. A variable of type int can hold integer numbers in the range -2,147,483,648 to 2,147,483,647. It takes 32 bits to store numbers in this range. The long data type is used for very large integers, with a size of up to 64 bits, in the range -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807! A float takes less memory (32 bits) than a double (64 bits), and the range varies. A char takes up 16 bits. When a primitive variable is declared, a specific amount of memory is reserved for it depending on its type. If you know the range of values that a variable will hold in your program, you can declare it with the appropriate data type for that range. The most commonly used data types are int for integer values and double for floating-point numbers.
Declaring and Initializing Primitive Variables
A primitive variable is declared by specifying its data type followed by its name. The following statement declares an integer variable called num1:
Note that the new keyword is not needed for primitives, and memory is reserved automatically for the variable num1 when it is declared.
Before a variable can be used, it must be assigned an initial value-this is known as initialization. The following statement initializes the variable num1 to the value 10:
num1 = 10;
A variable can be declared and initialized in a single statement. So we can also write:
int num1 = 10;
The following statement declares a floating-point variable of type float called num2 and initializes it to the value 1020.43:
float num2 = 1020.43f;
Although a float requires a suffix of letter "f" after the number, a double does not. Therefore, the following is valid:
double num3 = 32.56;