Pseudo-Random Numbers in Java

In many situations a program needs to generate a random number in a certain range. The Java Random class lets the programmer create objects of type Random and use them to generate a stream of random numbers (one at a time). The following declares the variable generator to be an object of type Random and instantiates it with the new operator.
```
     Random generator = new Random();
```
The generator object can be used to generate either integer or floating point random numbers using either the nextInt() or nextFloat() methods, respectively. The integer returned by nextInt could be any valid integer (positive or negative) whereas the number returned by nextFloat is a floating point value between 0 and 1 (up to but not including the 1). Most often the goal of a program is to generate a random integer in some particular range, say 30 to 99 (inclusive). There are two ways to do this:
- Using nextInt: This is the simplest technique:
```
        generator.nextInt(70) 
```
  will return a numbers between 0 and 69. Next, it may be necessary to shift the numbers must be shifted to a desired range by adding an appropriate value. So, the expression
```
	generator.nextInt(70) + 30
```
  will generate a number between 30 and 99.
- Using nextFloat: In this case, we must multiply the result of nextFloat to expand the range -- for example,
```
 
           generator.nextFloat() * 70
```
  returns a floating point number between 0 and 70 (up to but not including 70). To get the integer part of the number we use the cast operator:
```
         (int) (generator.nextFloat() * 70)
```
  The result of this is an integer between 0 and 69, so, as before
```
         (int) (generator.nextFloat() * 70) + 30
```
  shifts the numbers by 30 resulting in numbers between 30 and 99.
Download LuckyNumber.java and run it a few times:
```
// **************************************************
//   LuckyNumber.java
//
//   To generate two random "lucky" numbers 
// **************************************************
import java.util.Random;

public class LuckyNumber
{
   public static void main (String[] args)
   {
      Random generator = new Random();
      int lucky1, lucky2;   

      // Generate lucky1 (a random integer between 50 and 79) using the nextInt method

      lucky1 = generator.nextInt(30)+50;
 
      // Generate lucky2 (a random integer between 11 and 30) using nextFloat

      lucky2 = generator.nextInt(20)+11;

      System.out.println ("Your lucky numbers are " + lucky1 + " and " + lucky2);
    }
}
```