Generating Random Numbers in Java: A Comprehensive Guide - Prof. Martin Stepp, Study notes of Linux skills

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Copyright 2008 by Pearson Education

Building Java Programs

Chapter 5

Lecture 5-2: Random Numbers

reading: 5.1 - 5.2 self-check: #8 - 17

exercises: #3 - 6, 10, 12

videos: Ch. 5 #1-

Copyright 2008 by Pearson Education

The

Random

class

^

A^

Random

object generates pseudo-random* numbers.

^

Class

Random

is found in the

java.util

package.

import java.util.*;

^

Example: Random rand = new Random();int randomNumber =

rand.nextInt(10)

;^

// 0-

Method name

Description

nextInt()

returns a random integer

nextInt(

max

)^

returns a random integer in the range [0,

max

)

in other words, 0 to

max

-1 inclusive

nextDouble()

returns a random real number in the range [0.0, 1.0)

Copyright 2008 by Pearson Education

Random

questions

^

Given the following declaration, how would you get:

Random rand = new Random();

^

A random number between 1 and 100 inclusive? int random1 = rand.nextInt(100) + 1;

^

A random number between 50 and 100 inclusive? int random2 = rand.nextInt(51) + 50;

^

A random number between 4 and 17 inclusive? int random3 = rand.nextInt(14) + 4;

Copyright 2008 by Pearson Education

Random

and other types

^

nextDouble

method returns a

double

between 0.0 - 1.

^

Example: Get a random GPA value between 1.5 and 4.0: double randomGpa =

rand.nextDouble()

• 2.5 + 1.5;

^

Any set of possible values can be mapped to integers^

code to randomly play Rock-Paper-Scissors:^ int r = rand.nextInt(3);if (r == 0) {

System.out.println("Rock"); } else if (r == 1) {

System.out.println("Paper"); } else {

System.out.println("Scissors"); }

Copyright 2008 by Pearson Education

Random

answer

// Rolls two dice

until a sum of

7 is reached.

import

java.util.*;

public

class Dice

public

static

void

main(String[] args)

Random rand =

new Random();

int

tries

int

sum =

while (sum !=

// roll the dice

once

int roll

= rand.nextInt(6)

int roll

= rand.nextInt(6)

sum =

roll1 + roll2;

System.out.println(roll1 +

+ roll2 +

+ sum);

tries++;

} System.out.println("You

won after "

+ tries +

tries!");

Copyright 2008 by Pearson Education

Random

question

^

Write a multiplication tutor program.^

Ask user to solve problems with random numbersfrom 1-20.
The program stops after an incorrect answer. 14 * 8 =

^112

Correct!5 * 12 =

^60

Correct!8 * 3 =

^24

Correct!5 * 5 =

^25

Correct!20 * 14 =

^280

Correct!19 * 14 =

^256

Incorrect; the answer was 266You solved 5 correctly

Copyright 2008 by Pearson Education

Random

answer 2

... // Asks the user one multiplication problem,// returning the answer if they get it right and 0 if not. public static int askQuestion(Scanner console, Random rand) {

// pick two random numbers between 1 and 20 inclusive int num1 = rand.nextInt(20) +

int num2 = rand.nextInt(20) +

System.out.print(num1 + " * "

• num2 + " = ");

int guess = console.nextInt();if (guess == num

• num2) {

System.out.println("Correct!");return num1 *

num2;

} else {

System.out.println("Incorrect; the correct answer

was " +

(num1 * num2));

return 0; } } }