How to get a random integer in java?

Question

I'm trying to get a random integer, but the way I'm doing it takes a really long time to get that random number ( like 10 seconds!)

Random generator=new Random();
do {
    id=generator.nextInt();
}
while(id<=0||id>=4);

I'm trying to get a random number between (and include) 0 to 4 This code so far gets the job done, but 10 seconds is too long!

what is a better way to do this?

Thanks!

you dont need `while(id<=0||id>=4)` to check, simply specify the range `generator.nextInt(5);` — Baby, Feb 21 '14 at 07:24
i think this would help http://stackoverflow.com/questions/7961788/math-random-explained — Vijay Rahul, Feb 21 '14 at 07:25

score 10 · Accepted Answer · answered Feb 21 '14 at 07:22

You want

generator.nextInt(5);

which returns a random integer between 0 and 4. The reason why your original code took so long was because it was generating random integers over and over, until it got one between 1 and 3.

Note that as you were throwing away everything 0 or less, and everything 4 or more, you weren't even getting the range that you expected.

More information on the methods of the Random class can be found at http://docs.oracle.com/javase/7/docs/api/java/util/Random.html

+1 for link to documentation without succumbing to the temptation to be snarky or condescending. — jhericks, Feb 21 '14 at 18:53

score 1 · Answer 2 · answered Feb 21 '14 at 07:22

That's because you're generating literally probably billions of random numbers and throwing them away until you get one between 0 and 4. Instead:

id = generator.nextInt(5); // number between 0 and 4, inclusive

In the future, please read the documentation for the classes you're using; this is clearly explained in the Javadoc.

score 1 · Answer 3 · answered Feb 21 '14 at 07:23

1

Use Math.random() cast it into int

int i=(int)Math.random()*4;

answered Feb 21 '14 at 07:23

Nambi

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Better to use the built-in `nextInt(int)` method. It's more transparent and faster. – chrylis -cautiouslyoptimistic- Feb 21 '14 at 07:24

score 0 · Answer 4 · answered Feb 21 '14 at 07:24

Just include the upper bound (assuming you want 1, 2, or 3):

id = 1 + generator.nextInt(3);

From the javadoc:

public int nextInt(int n)

Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.

score 0 · Answer 5 · answered Feb 21 '14 at 07:24

0

try this:

Random random = new Random();
random.nextInt(4);

answered Feb 21 '14 at 07:24

A N M Bazlur Rahman

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How to get a random integer in java?

5 Answers5