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!

Answer 1

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

Answer 2

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 .

Answer 3

使用Math.random（ ）将其强制转换为int

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

Answer 4

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.

Answer 5

try this:

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