Data Types

General programming data types

Boolean - Represents only true or false values. These are used in logic expressions and decisions.

Integer - Represents positive or negative whole numbers without a fractional part. Examples: -127, 8, 65535.

Floating Point - Represents positive or negative numbers with a fractional component. Examples: 3.1415, 2.0, -123.456.

String - Represents textual information as a sequence of encoded characters. Examples: "Hello!", "This is a String.".

Java Primitive Data Types

Type	Description
byte	Integers (whole numbers) in the range of -128 to +127
short	Integers in the range of -32,768 to +32,767
int	Integers in the range of -2,147,483,648 to +2,147,483,647
long	Integers in the range of -9,223,372,036,854,775,808 to +9,223,372,036,854,775,807
float	Real numbers in the range of ±3.40282347 x 1038 to 1.40239846 x 10-45
double	Real numbers in the range of ±1.7976931348623157 x 10308 to 4.9406564584124654 x 10-324
char	Any single character
boolean	Only two values: true and false

Numerical Precision

A float value has a precision of about 9 significant digits, and a double value has a precision of about 17 significant digits. It is generally best to assume that the last digit of any float or double value is rounded and may not be exact.

Floating point literals

A floating-point literal using scientific notation is written using an e preceding the power-of-10 exponent, as in 6.02e23 to represent 6.02 x 1023. The e stands for exponent. Likewise, 0.001 is 1 x 10-3 and can be written as 1.0e-3. For a floating-point literal, good practice is to make the leading digit non-zero.

Generating a random number

The Random class provides methods that return a random integer in the range to or a programmer-defined range.

import java.util.Random;

public class ThreeRandomValues {
   public static void main(String[] args) {
      Random randGen = new Random();  // New random number generator

      System.out.println(randGen.nextInt());
      System.out.println(randGen.nextInt());
      System.out.println(randGen.nextInt());

The statement import java.util.Random; enables use of the Random class. The statement Random randGen = new Random(); creates a new random number generator object named randGen. The method call randGen.nextInt() can then be used to get a random integer ranging from to .

A programmer can specify the seed when the Random object is created, as in Random randGen = new Random(5); or using the setSeed() method, as in randGen.setSeed(5); With a specific seed, each program run will yield the same sequence of pseudo-random numbers.