Generate random numbers
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:

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```

Would you use this technique?
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