Building Java Programs, 4th edition

Lab: Random Numbers

Except where otherwise noted, the contents of this document are Copyright 2013 Stuart Reges and Marty Stepp.

lab document created by Marty Stepp, Stuart Reges and Whitaker Brand

Lab goals

Goals for this problem set:

• use Random objects to produce random numbers
• Where you see this icon, you can click it to check the problem in Practice-It!

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

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

Try solving this problem in Practice-It! from the link above.