Random Numbers
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Fran Trees Drew University 1 Random Numbers and simulations…. Section 6.5
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Random Numbers. and simulations…. Section 6.5. Random Number Generators. Random number generators are used to simulate events. Java provides the Random class which implements a random number generator . This random number generator can produce random integers and random double numbers. - PowerPoint PPT Presentation
Transcript of Random Numbers
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Random Numbers
and simulations….
Section 6.5
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Random Number Generators
Random number generators are used to simulate events.
Java provides the Random class which implements a random number generator.
This random number generator can produce random integers and random double numbers.
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class java.util.Random
Method Method Summary
int nextInt(n) Returns a random integer in the range from 0 to n-1 inclusive.
double nextDouble() Returns a random floating-point number between 0 (inclusive) and 1 (exclusive).
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Sample use:
Random generator = new Random(); // Constructs the number generator.
int randInt = generator.nextInt(10);// Generates a random integer from 0-9 inclusive.
double randDouble = generator.nextDouble();// Generates a random double from 0(inclusive) to 1
(exclusive).
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Die class using Randomimport java.util.Random; public class Die{ public Die(int s) { sides = s; generator = new Random(); } public int cast() { return 1 + generator.nextInt(sides); } private Random generator; private int sides;}
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DieTest.java/** This program simulates casting a die ten times.*/public class DieTest{ public static void main(String[] args) { Die d = new Die(6); final int TRIES = 10; for (int i = 1; i <= TRIES; i++) { int n = d.cast(); System.out.print(n + " "); } System.out.println(); }}
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DieTest.java/** This program simulates casting a die ten times.*/public class DieTest{ public static void main(String[] args) { Die d = new Die(6); final int TRIES = 10; for (int i = 1; i <= TRIES; i++) { int n = d.cast(); System.out.print(n + " "); } System.out.println(); }}
1 6 4 3 2 2 6 2 5 4
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Caution:
When writing programs that include random numbers, two Random objects created within the same millisecond will have the same sequence of random numbers.
If the following declarations are executed in the same millisecond,
Random generator1 = new Random();Random generator2 = new Random();
generator1 and generator2 will generate same sequence of random numbers.
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Die class using Randomimport java.util.Random; public class Die{ public Die(int s) { sides = s; generator = new Random(); } public int cast() { return 1 + generator.nextInt(sides); } private Random generator; private int sides;}
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Roll two dice ten times. Record results.Consider the following first attempt!
public class DieTestForTwo{ public static void main(String[] args) { Die d = new Die(6); Die d2 = new Die(6); final int TRIES = 10; for (int i = 1; i <= TRIES; i++) { int n = d.cast(); int n2 = d2.cast(); System.out.println(n + " " + n2); } System.out.println(); }}
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Results:
6 6
2 2
1 1
6 6
4 4
6 6
6 6
3 3
3 3
5 5
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Results:
6 6
2 2
1 1
6 6
4 4
6 6
6 6
3 3
3 3
5 5
What happened?????
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What happened and why?
6 6
2 2
1 1
6 6
4 4
6 6
6 6
3 3
3 3
5 5
public class DieTestForTwo{ public static void main(String[] args) { Die d = new Die(6); Die d2 = new Die(6); final int TRIES = 10; for (int i = 1; i <= TRIES; i++) { int n = d.cast(); int n2 = d2.cast(); System.out.println(n + " " + n2); } System.out.println(); }}
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Another attempt:
public class DieTestForTwo{ public static void main(String[] args) { Die d = new Die(6); final int TRIES = 10; for (int i = 1; i <= TRIES; i++) { int n = d.cast(); int n2 = d.cast(); System.out.println(n + " " + n2); } System.out.println(); }}
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New results:
2 1
1 4
3 3
5 6
6 6
4 6
2 2
5 1
3 6
2 1
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Is this the desired outcome? The difference?2 1
1 4
3 3
5 6
6 6
4 6
2 2
5 1
3 6
2 1
public class DieTestForTwo{ public static void main(String[] args) { Die d = new Die(6); final int TRIES = 10; for (int i = 1; i <= TRIES; i++) { int n = d.cast(); int n2 = d.cast(); System.out.println(n + " " + n2); } System.out.println(); }}
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Problem
Write a test program for the Die class that will roll two 6-sided dice until "doubles" are rolled. Write to the screen the number of rolls it took until doubles.
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A possible solution…
Die d = new Die(6);
int countRolls = 1;
while(d.cast() != d.cast())
{
countRolls++;
}
System.out.println(countRolls);
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A possible solution with results…
Die d = new Die(6);
int countRolls = 1;
while(d.cast() != d.cast())
{
countRolls++;
}
System.out.println(countRolls);
5
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Suppose I want to "see" the rolls?
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Suppose I want to "see" the rolls?
Die d = new Die(6);int countRolls = 1;while(d.cast() != d.cast()){ countRolls++; System.out.println(d.cast() + " " + d.cast())}System.out.println(countRolls);
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Suppose I want to "see" the rolls?
Die d = new Die(6);int countRolls = 1;while(d.cast() != d.cast()){ countRolls++; System.out.println(d.cast() + " " + d.cast())}System.out.println(countRolls);
Doubles3 64 63 35 65
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Suppose I want to "see" the rolls?
Die d = new Die(6);int countRolls = 1;while(d.cast() != d.cast()){ countRolls++; System.out.println(d.cast() + " " + d.cast())}System.out.println(countRolls);
Doubles3 64 63 35 65
What happened?
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A solution:
Die d = new Die(6);int countRolls = 1;int roll1=d.cast();int roll2=d.cast();System.out.println(roll1 + " " + roll2);while(roll1 != roll2){ countRolls++; int roll1=d.cast(); int roll2=d.cast(); System.out.println(roll1 + " " + roll2); }System.out.println(countRolls);
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A solution with results:
Die d = new Die(6);int countRolls = 1;int roll1=d.cast();int roll2=d.cast();System.out.println(roll1 + " " + roll2);while(roll1 != roll2){ countRolls++; roll1=d.cast(); roll2=d.cast(); System.out.println(roll1 + " " + roll2); }System.out.println(countRolls);
6 54 24 55 63 35
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Another choice for a loop?
d = new Die(6);countRolls = 0;do{ countRolls++; roll1=d.cast(); roll2=d.cast(); System.out.println(roll1 + " " + roll2);
}while(roll1 != roll2);System.out.println(countRolls);
1 41 66 26 14 45
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Remember….
It is a better idea to share a single random number generator in the entire program.
We rarely want to generate identical sequences of random numbers!
