randon number

[john mor]

I try to print out 6 random numbers from 40 numbers
ex( 20,5,1,40,31,29)
the program which I have writen is ok, but I don't want that the program writes a random number more than one time.
ex 20,5,1,40,31,29) is ok
ex 20,5,5,40,31,29) is wrong. // how do I fix it?

[Mark Van Tuyl]

Once a number has been selected, set it to -1 (or some other invalid value). Before displaying a number, make sure it's valid. Otherwise, select another.

[john mor]

If I want to print out 6 nbrs

for(int i=0; i<6; i++)
and set a nbr to -1
the program dose not print out 6 different nbr, may be 5 or 4 nbrs.

[Mark Van Tuyl]

Correct. If you have selected an invalid number, you must decrement the counter.

[Jesper de Jong]

What does your code look like? How do you store those 40 numbers in your program; in an array or one of the Java collections?

If you have the numbers in a java.util.List, you can use the method java.util.Collections.shuffle(...) to shuffle the elements in the list, and then you just take the first 6 numbers out of the shuffled list.