Random.nextInt(number)함수는 0부터 number를 제외한 이하의 수치값을 반환한다
There are two principal means of generating random (really pseudo-random) numbers:
- the Random class generates random integers, doubles, longs and so on, in various ranges.
- the static method Math.random generates doubles between 0 (inclusive) and 1 (exclusive).
To generate random integers:
- do not use Math.random (it produces doubles, not integers)
- use the Random class to generate random integers between 0 and N.
To generate a series of random numbers as a unit, you need to use a single Random object - do not create a new Random object for each new random number.
Other alternatives are:
- SecureRandom, a cryptographically strong subclass of Random
- ThreadLocalRandom, intended for multi-threaded cases
Here are some examples using Random.
Example 1
import java.util.Random;
/** Generate 10 random integers in the range 0..99. */
public final class RandomInteger {
public static final void main(String... aArgs){
log("Generating 10 random integers in range 0..99.");
//note a single Random object is reused here
Random randomGenerator = new Random();
for (int idx = 1; idx <= 10; ++idx){
int randomInt = randomGenerator.nextInt(100);
log("Generated : " + randomInt);
}
log("Done.");
}
private static void log(String aMessage){
System.out.println(aMessage);
}
}
Example run of this class:
Generating 10 random integers in range 0..99. Generated : 44 Generated : 81 Generated : 69 Generated : 31 Generated : 10 Generated : 64 Generated : 74 Generated : 57 Generated : 56 Generated : 93 Done.
Example 2
This example generates random integers in a specific range.
import java.util.Random;
/** Generate random integers in a certain range. */
public final class RandomRange {
public static final void main(String... aArgs){
log("Generating random integers in the range 1..10.");
int START = 1;
int END = 10;
Random random = new Random();
for (int idx = 1; idx <= 10; ++idx){
showRandomInteger(START, END, random);
}
log("Done.");
}
private static void showRandomInteger(int aStart, int aEnd, Random aRandom){
if (aStart > aEnd) {
throw new IllegalArgumentException("Start cannot exceed End.");
}
//get the range, casting to long to avoid overflow problems
long range = (long)aEnd - (long)aStart + 1;
// compute a fraction of the range, 0 <= frac < range
long fraction = (long)(range * aRandom.nextDouble());
int randomNumber = (int)(fraction + aStart);
log("Generated : " + randomNumber);
}
private static void log(String aMessage){
System.out.println(aMessage);
}
}
An example run of this class:
Generating random integers in the range 1..10. Generated : 9 Generated : 3 Generated : 3 Generated : 9 Generated : 4 Generated : 1 Generated : 3 Generated : 9 Generated : 10 Generated : 10 Done.
Example 3
This example generates random floating point numbers in a Gaussian (normal) distribution.
import java.util.Random;
/**
Generate pseudo-random floating point values, with an
approximately Gaussian (normal) distribution.
Many physical measurements have an approximately Gaussian
distribution; this provides a way of simulating such values.
*/
public final class RandomGaussian {
public static void main(String... aArgs){
RandomGaussian gaussian = new RandomGaussian();
double MEAN = 100.0f;
double VARIANCE = 5.0f;
for (int idx = 1; idx <= 10; ++idx){
log("Generated : " + gaussian.getGaussian(MEAN, VARIANCE));
}
}
private Random fRandom = new Random();
private double getGaussian(double aMean, double aVariance){
return aMean + fRandom.nextGaussian() * aVariance;
}
private static void log(Object aMsg){
System.out.println(String.valueOf(aMsg));
}
}
An example run of this class:
Generated : 99.38221153454624 Generated : 100.95717075067498 Generated : 106.78740794978813 Generated : 105.57315286730545 Generated : 97.35077643206589 Generated : 92.56233774920052 Generated : 98.29311772993057 Generated : 102.04954815575822 Generated : 104.88458607780176 Generated : 97.11126014402141
