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Generate random numbers using Math.random

  1. /*
  2.   Generate random numbers using Math.random
  3.   This java example shows how to generate random numbers using random method of
  4.   Java Math class.
  5. */
  6.  
  7. public class GenerateRandomNumbers {
  8.  
  9.   public static void main(String[] args) {
  10.  
  11.     /*
  12.      * To generate random numbers, use
  13.      * static double random() method of Java Math class.
  14.      *
  15.      * This method returns a positive double value grater than 0.0
  16.      * and less than 1.0
  17.     */
  18.  
  19.     System.out.println("Random numbers between 0.0 and 1.0 are,");
  20.     for(int i=0; i < 5 ; i++)
  21.       System.out.println("Random Number ["+ (i+1) + "] : " + Math.random());
  22.  
  23.     /*
  24.      * To generate random number between 1 to 100 use following code
  25.      */
  26.  
  27.     System.out.println("Random numbers between 1 and 100 are,");
  28.     for(int i=0; i < 5 ; i++)
  29.       System.out.println("Random Number ["+ (i+1) + "] : " + (int)(Math.random()*100));
  30.  
  31.   }
  32. }
  33.  
  34. /*
  35. Typical output would be
  36. Random numbers between 0.0 and 1.0 are,
  37. Random Number [1] : 0.7900395454653136
  38. Random Number [2] : 0.15887365598103076
  39. Random Number [3] : 0.5570570713930629
  40. Random Number [4] : 0.017811004461356195
  41. Random Number [5] : 0.7135560403213513
  42.  
  43. Random numbers between 1 and 100 are,
  44. Random Number [1] : 31
  45. Random Number [2] : 21
  46. Random Number [3] : 24
  47. Random Number [4] : 95
  48. Random Number [5] : 3
  49. */

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It didnt' work out for mw

Submitted by Anonymous on Fri, 06/12/2009 - 11:18.

Hi,
i am tryigb to figuer out the Math.random class, ti randomly creates numbers
of type Double, right? so if i want to create numbers between 0-100, your second method should work, isn't it?
however, i copy paste your code the IDE, and it kept do give me the followign exceptions:

at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$000(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
Exception in thread "main"

Thanks, Gil

How to generate a random int (sorry I typed it in my Java IDE)

Submitted by Anonymous on Wed, 08/12/2009 - 15:06. 

  1. //As you might know, Math.random() generates a random double where X<0 
  2. //To generate a random int using the same method (ie Math.random()) you do the //following:
  3.  
  4. public class RandomInt{
  5. 	public static void main(String[] args){
  6. 		int random = (int)(Math.random()*10)+5; //*see bottom
  7. 		System.out.println(random);
  8. 	}
  9. }
  10. //the "(int)" parses the double to an int value
  11. //replace 10 with your range of numbers 
  12. //(ie if you want a number between 5 and 15 the range is 10 [15-5]
  13. //replace the 5 with the staring number
  14. //(ie if you want the lowest number in the range to be 5 then add 5)
  15. //another eg.
  16. //int ran = (int)(Math.random()*100)-50;
  17. //will return a value in the range [-50;50]

Question

Submitted by Anonymous on Fri, 10/23/2009 - 23:15.

Can anyone tell me what this code does and what it means

System.out.println((int)(6*Math.random())+1);

Don't misunderstand

Submitted by Anonymous on Fri, 11/13/2009 - 16:34.

It means generate a random number from the six consecutive numbers starting from 1. That means any number from 1,2,3,4,5,6. It does NOT mean any number from 1 to 6.

How about this code?

  1. System.out.println((int)(6*Math.random())+4);

Will it give you random number from range 4-6? NO! It will give you random numbers from range 4-9! Reason: The six consecutive numbers starting from 4 are 4,5,6,7,8,9.

If you want random numbers from 4-6, you must use this code:

  1. System.out.println((int)( (6-4+1) *Math.random())+4);

OR
  1. System.out.println((int)(3*Math.random())+4);

It is good

Submitted by Anonymous on Sat, 11/14/2009 - 15:42.

It is good


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