Random integer generator question

[Travis Hagan]

Howdy, I had a quick question that I hope someone could provide an answer to. I created this program to fill an array with integers. All it does is randomly generate (or psuedo randomly) a number and store it in the first box and then second... until I run out of boxes. Usually after running this once or twice I get a bunch of zeros. Any ideas why???

Here's the code in case that is any more revealing:

public void fillArray()
    {
        size = 10;
        numberArray = new int[size];
        while(size > sizeCheck)
        {
            randomGenerator = new Random();
            int index = randomGenerator.nextInt(100000);
            numberArray[sizeCheck] = index;
            sizeCheck++;
        }
        
    } 

PS: if there is a better way to generate random numbers, I'm all ears.

[Vijitha Kumara]

How is your sizeCheck's gets initialized? Apart from that I can't see anything wrong which wouldn't give the expected result.

[Duc Vo]

Travis Hagan wrote:Howdy, I had a quick question that I hope someone could provide an answer to. I created this program to fill an array with integers. All it does is randomly generate (or psuedo randomly) a number and store it in the first box and then second... until I run out of boxes. Usually after running this once or twice I get a bunch of zeros. Any ideas why???

Here's the code in case that is any more revealing:

public void fillArray()
    {
        size = 10;
        numberArray = new int[size];
        while(size > sizeCheck)
        {
            randomGenerator = new Random();
            int index = randomGenerator.nextInt(100000);
            numberArray[sizeCheck] = index;
            sizeCheck++;
        }
        
    } 

PS: if there is a better way to generate random numbers, I'm all ears.

Try to move line 7 out of while loop. It should work.

[Travis Hagan]

I removed line 7 but it didn't work. Null pointer exception. Turns out that after running certain methods the size check would be too high so that when I ran the iteration it created the array but didn't fill.

Sometimes things are more simple than they appear.

[Campbell Ritchie]

It didn't mean to remove the line; it meant to move it to before the loop.

[Travis Hagan]

Sorry, I missed that. I get in the habit of reading way too fast. It works either way, and moving out the loop should save the PC a minimalistic amount of time but all the same.

[Campbell Ritchie]

Minimal? Not for Random. The real problem with Random (much less of a problem with Java5/6 than with Java1.4) is that when you create two instances, there is a risk of them both producing the same sequence of numbers. So you ought to avoid creating new Random objects, and use the same instance, as far as possible.

By the way: if you look in the Random API it says java.lang.Math.Random() is often easier to use.