A literal is a constant value that appears directly in a program.

Integer Literals

An integer literal can be assigned to an integer variable as long as it can fit into the variable. A compile error will occur if the literal is too large for the variable to hold. The statement byte b = 128, for example, will cause a compile error, because 128 cannot be stored in a variable of the byte type. (Note that the range for a byte value is from –128 to 127.)

An integer literal is assumed to be of the int type, whose value is between -231 (-2147483648) and 231 - 1 (2147483647). To denote an integer literal of the long type, append the letter L or l to it. For example, to write integer 2147483648 in a Java program, you have to write it as 2147483648L or 2147483648l, because 2147483648 exceeds the range for the int value. L is preferred because l (lowercase L) can easily be confused with 1 (the digit one).

By default, an integer literal is a decimal integer number. To denote a binary integer literal, use a leading 0b or 0B (zero B), to denote an octal integer literal, use a leading 0 (zero), and to denote a hexadecimal integer literal, use a leading 0x or 0X (zero X). For example,

System.out.println(0B1111); // Displays 15
System.out.println(07777); // Displays 4095
System.out.println(0XFFFF); // Displays 65535

Floating-Point Literals

Floating-point literals are written with a decimal point. By default, a floating-point literal is treated as a double type value. For example, 5.0 is considered a double value, not a float value. You can make a number a float by appending the letter f or F, and you can make a number a double by appending the letter d or D. For example, you can use 100.2f or 100.2F for a float number, and 100.2d or 100.2D for a double number. The double type values are more accurate than the float type values.

Scientific Notation

Floating-point literals can be written in scientific notation in the form of a * 10^b . For example, the scientific notation for 123.456 is 1.23456 * 10^2 and for 0.0123456 is 1.23456 * 10^-2 . A special syntax is used to write scientific notation numbers. For example, 1.23456 * 10^2 is written as 1.23456E2 or 1.23456E+2 and 1.23456 * 10^-2 as 1.23456E-2. E (or e) represents an exponent and can be in either lowercase or uppercase.

The float and double types are used to represent numbers with a decimal point. Why are they called floating-point numbers? These numbers are stored in scientific notation internally. When a number such as 50.534 is converted into scientific notation, such as 5.0534E+1, its decimal point is moved (i.e., floated) to a new position.

To improve readability, Java allows you to use underscores between two digits in a number literal. For example, the following literals are correct.

long ssn = 232_45_4519;
long creditCardNumber = 2324_4545_4519_3415L;

However, 45_ or _45 is incorrect. The underscore must be placed between two digits.