Random Numbers in Java
Presentation
•
Computers
•
9th - 12th Grade
•
Medium
Lisa Donlan
Used 10+ times
FREE Resource
7 Slides • 8 Questions
1
Random Numbers in Java
by Lisa Donlan
2
3
How do random numbers work?
Math.random() returns a random number between 0.0-0.99.
(int)(Math.random( )*range) + min moves the random number into a range starting from a minimum number.
The range is the (max number - min number + 1).
4
What do you think the output is?
public class Test3
{
public static void main(String[ ] args)
{
System.out.println(Math.random());
System.out.println(Math.random());
}
}
5
One possible result is
0.3842967819081746
0.30067392084109024
System.out.println(Math.random());
System.out.println(Math.random());
6
Multiple Choice
What does
double rnd=Math.random( );
return?
returns a random number between 0.0-0.99
returns a random number between 0.0-1.00
returns a random number between 0 and 1
a negative number
7
How do you use random to choose numbers?
Example: Randomly choose numbers on a die.
8
Multiple Choice
int rnd2=(int)(Math.random( )∗10)+1;
System.out.print(rnd1);
What is the output?
any integer between 1 and 10 exclusive
any integer between 1 and 10 inclusive
any integer between 0 and 10 inclusive
any integer between 0 and 10 exclusive
9
Multiple Choice
How would you choose the numbers from 1 to 100?
System.out.println((int) (Math.random( ) * 10)+10);
System.out.println((int) (Math.random( ) * 10)+100);
System.out.println((int) (Math.random( ) * 100)+100);
System.out.println((int) (Math.random( ) * 100)+1);
10
How do you get a random number you can use?
// rnd1 is an integer in the range 0-9 (including 9).
int rnd1 = (int)(Math.random( ) * 10);
Explain to your shoulder partner
Why do we have to use (int)?
What is this called (the concept is tested on the AP test EVERY year!!)?
Why do we have to multiply by 10?
11
Multiple Choice
Which of the following would be true about 40% of the time?
Math.random() > 0.4
Math.random( ) < 0.4
Math.random() == 0.4
12
Multiple Choice
Which of the following would return a random number from 1 to 5 inclusive?
((int) (Math.random( ) * 5))
((int) (Math.random( ) * 6))
((int) (Math.random( ) * 5) + 1)
13
Multiple Choice
Which of the following would return a random number from 0 to 10 inclusive?
((int) (Math.random( ) * 11))
((int) (Math.random( ) * 10))
((int) (Math.random( ) * 10) + 1)
14
Multiple Choice
Which of the following would be true about 75% of the time?
Math.random( ) < 0.25
Math.random( ) == 0.25
Math.random( ) > 0.25
15
Multiple Choice
Which of the following statements assigns a random integer between 25 and 60, inclusive, to rn?
This is a released AP MC question.
int rn = (int) (Math.random( ) * 25) + 36;
int rn = (int) (Math.random( ) * 36) + 25;
int rn = (int) (Math.random( ) * 25) + 60;
int rn = (int) (Math.random( ) * 60) + 25;
int rn = (int) (Math.random( ) * 26) + 60;
Random Numbers in Java
by Lisa Donlan
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