Random Behavior

The Random Class

• Most computer behavior depends only on user input, data from files, etc.
• Another way, though, to produce a variety of results is to introduce randomness through pseudo-random numbers.

  Pseudo-random numbers look and work like random numbers, but are generated from computer algorithms and so are not truly random.




An object of the Random class is actually a generator of random numbers, not a random object itself. Just as a die can be used to generate a random number between 1 and 6, or a coin can be used to generate heads or tails, a Random object can be used to generate random numbers or true/false values. For example, the code

        Random generator = new Random();
        int randNum = generator.nextInt(10);

creates a random number generator and uses it to generate one of the 10 numbers between 0 and 9 (the parameter specifies the number of possible values). If we call nextInt(10) repeatedly, we'll get a sequence of pseudo-random numbers in that range, such as:

        8, 5, 0, 0, 4, 3, 1, 3, 1, 0, 3, 6, 7, 0, 4, 4, 3, 9, 2, 8, ...

• The Random class is in the java.util package.

Example: Using a Random Number to Drive Random Behavior

Consider a program simulating a person at lunch who randomly chooses between a cookie or an apple for dessert.

student.takeASandwich();
student.takeCoffee();
Random generator = new Random();
int randNum = generator.nextInt(2);
if ( randNum == 0 )
    student.takeAnApple();
else
    student.takeACookie();
student.sitDownAndEat();