acm.util

Class RandomGenerator

java.lang.Object

java.util.Random

acm.util.RandomGenerator

All Implemented Interfaces:

java.io.Serializable

public class RandomGenerator
extends java.util.Random

This class implements a simple random number generator that allows clients to generate pseudorandom integers, doubles, booleans, and colors. To use it, the first step is to declare an instance variable to hold the random generator as follows:

private RandomGenerator rgen = RandomGenerator.getInstance();

When you then need to generate a random value, you call the appropriate method on the rgen variable.

The RandomGenerator class is actually implemented as an extension to the Random class in java.util. The new version has the following advantages over the original:

• The name of the class emphasizes that the object is a random generator rather than a random value.

• The class includes overloaded versions of nextInt and nextDouble to simplify choosing numbers in a specific range.

• The method nextBoolean is overloaded to allow the specification of a probability.

• The class includes a method nextColor that generates a random opaque color.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
RandomGenerator() Creates a new random generator initialized to an unpredictable starting point.

Method Summary

Methods

Modifier and Type	Method and Description
static RandomGenerator	getInstance() This method returns a RandomGenerator instance that can be shared among several classes.
boolean	nextBoolean() Returns a random boolean value that is true or false with equal probability.
boolean	nextBoolean(double p) Returns a random boolean value with the specified probability.
java.awt.Color	nextColor() Returns a random opaque Color whose components are chosen uniformly in the 0-255 range.
double	nextDouble(double low, double high) Returns the next random real number in the specified range.
int	nextInt(int n) Returns the next random integer between 0 and n-1, inclusive.
int	nextInt(int low, int high) Returns the next random integer in the specified range.

Methods inherited from class java.util.Random

nextBytes, nextDouble, nextFloat, nextGaussian, nextInt, nextLong, setSeed

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

RandomGenerator

public RandomGenerator()

Creates a new random generator initialized to an unpredictable starting point. In almost all programs, you want to call this method once to produce a single generator object, which you then use each time you need to generate a random value. If you create several random generators in succession, they will typically generate the same sequence of values.

During debugging, it is often useful to set the internal seed for the random generator explicitly so that it always returns the same sequence. To do so, you need to invoke the setSeed method.

Method Detail

nextInt

public int nextInt(int n)

Returns the next random integer between 0 and n-1, inclusive. This method is in modern implementations of the Random class, but is missing from JDK 1.1.

Overrides:

nextInt in class java.util.Random

nextBoolean

public boolean nextBoolean()

Returns a random boolean value that is true or false with equal probability. This method is in modern implementations of the Random class, but is missing from JDK 1.1.

Overrides:

nextBoolean in class java.util.Random

nextInt

public int nextInt(int low,
          int high)

Returns the next random integer in the specified range. For example, you can generate the roll of a six-sided die by calling

rgen.nextInt(1, 6);

or a random decimal digit by calling

rgen.nextInt(0, 9);

Parameters:

low - The low end of the range

high - The high end of the range

Returns:

The next random int between low and high, inclusive

nextDouble

public double nextDouble(double low,
                double high)

Returns the next random real number in the specified range. The resulting value is always at least low but always strictly less than high. You can use this method to generate continuous random values. For example, you can set the variables x and y to specify a random point inside the unit square as follows:

double x = rgen.nextDouble(0.0, 1.0);
double y = rgen.nextDouble(0.0, 1.0);

Parameters:

low - The low end of the range

high - The high end of the range

Returns:

A random double value d in the range low ≤ d < high

nextBoolean

public boolean nextBoolean(double p)

Returns a random boolean value with the specified probability. You can use this method to simulate an event that occurs with a particular probability. For example, you could simulate the result of tossing a coin like this:

String coinFlip = rgen.nextBoolean(0.5) ? "HEADS" : "TAILS";

Parameters:

p - A value between 0 (impossible) and 1 (certain) indicating the probability

Returns:

The value true with probability p

nextColor

public java.awt.Color nextColor()

Returns a random opaque Color whose components are chosen uniformly in the 0-255 range.

Returns:

A random opaque Color

getInstance

public static RandomGenerator getInstance()

This method returns a RandomGenerator instance that can be shared among several classes.

Returns:

A shared RandomGenerator object