Building Java Programs

Lab: Random Numbers

Except where otherwise noted, the contents of this document are Copyright 2019 Stuart Reges and Marty Stepp.

Lab goals

Goals for this problem set:

Random methods

To use these methods, you need a variable of type Random in scope:

Random randy = new Random();
int aRandomNumber = randy.nextInt(10);  // 0-9
Method name Returns...
nextInt() a random integer
nextInt(max) a random integer between 0 (inclusive) and max (exclusive)
nextDouble() a random real number between 0.0 and 1.0
nextBoolean() a random boolean value: true or false

Exercise : Random expressions

Fill in the boxes to produce expressions that will generate random numbers in the provided ranges. Assume that the following Random variable has been declared:

Random rand = new Random();
Example: a random integer from 1 to 5 inclusive: rand.nextInt(5) + 1
a random integer from 0 to 3 inclusive: rand.nextInt(4)
a random integer from 5 to 10 inclusive: rand.nextInt(6) + 5
a random integer from -4 to 4 inclusive: rand.nextInt(9) - 4
a random even integer from 16 to 28 inclusive:
(Hint: To get only even numbers, scale up.)
rand.nextInt(7) * 2  + 16

Exercise : makeGuesses practice-it

Write a method named makeGuesses that will output random numbers between 1 and 50 inclusive until it outputs one of at least 48. Output each guess and the total number of guesses made. Below is a sample execution:

guess = 43
guess = 47
guess = 45
guess = 27
guess = 49
total guesses = 5