Any one who considers arithmetical methods of producing random digits is, of course, in a state of sin. For, as has been pointed out several times, there is no such thing as a random number — there are only methods to produce random numbers and a strict arithmetic procedure, of course, is not such a method.
~ John von Neumann (19031228 19570208 age:53)
There are two kinds of random numbers, pseudorandom numbers that can be rapidly generated from mathematical formulae and true random numbers, generated from some random physical process such as radioactive decay. Pseudorandom numbers are useless for cryptography. You need true random numbers for that. You now probably want to follow the link to pseudorandom numbers.
Collections.shuffle will scramble the objects in an ArrayList.
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