[SOLVED] Random number is not working

Everytime I run this random 4 digit number and 8 digit number outputs as 0. If you could help me and point out what I am doing wrong thatwould be great. Thanks!:)

import javax.swing.JOptionPane;

public class generateAccountNumber{
public static void main(String[] args){


String bankId = "A4326";
String result = "";
final String BANK_ID = "A4326";
int[]randNums4 = new int[1000];
int[]randNums8 = new int[1000];
int i;

String firstName = JOptionPane.showInputDialog("First Name:");
firstName.toUpperCase();
String lastName = JOptionPane.showInputDialog("Last Name:");
lastName.toUpperCase();

for(i = 0;i<=randNums4.length && i>999;i++){
randNums4[i] = (int)(8999.0*Math.random()+1000);
System.out.println(randNums4[i]);
}

for(i = 0;i<=randNums8.length && i>9999999;i++){
randNums8[i] = (int)(89999999.0*Math.random()+10000000);
System.out.println(randNums8[i]);
}
result += BANK_ID+"-"+lastName.charAt(0)+firstName.charAt(0)+"-"+randNums4[i]+"-"+Character.toUpperCase(lastName.charAt(1))+Charac ter.toUpperCase(firstName.charAt(1))+"-"+randNums8[i];
System.out.println(result);
}


}

How many times do those for loops get executed?

Code:

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for(i = 0;i<=randNums4.length && i>999;i++){
    System.out.println("i=" + i);
    randNums4[i] = (int)(8999.0*Math.random()+1000);
    System.out.println(randNums4[i]);
}

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@OP, Do you know what's the meaning of this.

Code:

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for(i = 0;i<=randNums4.length && i>999;i++){

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What happen when start to run this line of code?

I think pbrockway2 try to explain the same thing.

Quote:

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Originally Posted by pbrockway2

How many times do those for loops get executed?

Code:

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for(i = 0;i<=randNums4.length && i>999;i++){
    System.out.println("i=" + i);
    randNums4[i] = (int)(8999.0*Math.random()+1000);
    System.out.println(randNums4[i]);
}

---

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It will loop to the length of the array (i.e if the array has 1000 elements it will loop 1000 times) where 'i' starts at 0 but will go straight to 1,000 and beyond

Quote:

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It will loop to the length of the array (i.e if the array has 1000 elements it will loop 1000 times) where 'i' starts at 0 but will go straight to 1,000 and beyond

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No it doesn't. Try the code I posted (complete with the System.out.println()) and see what it really does.

Quote:

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Originally Posted by pbrockway2

No it doesn't. Try the code I posted (complete with the System.out.println()) and see what it really does.

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It does nothing!

It just outputs:

A4326-MA-0-AN-0

The 0's are the problem

What if you try using Math.random()?

Quote:

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Originally Posted by Natrix

What if you try using Math.random()?

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I am using Math.random()

Quote:

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Originally Posted by anthonym2121

It does nothing!

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Correct.

Quote:

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Originally Posted by anthonym2121

It just outputs:

A4326-MA-0-AN-0

The 0's are the problem

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No, the problem is not those zeros; the problem is that your for loops do nothing. (ie loop precisely zero times).

I am still not sure what you expected the loop to do. Perhaps you could explain this: is the array expected to grow in size?

You talk about i "going to straight to 1000 and beyond". But if this really were to happen the best you could expect would be an ArrayIndexOutOfBoundsException because randNums4[i] doesn't exist when i is 1000 or bigger.

Oh sorry didn't see it.

Code:

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for(i = 0;i<=randNums4.length && i>999;i++){

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Code:

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  for(i = 0;i<=randNums8.length && i>9999999;i++){

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In both the for loops, conditions are not satisfied.
Let us take first 'for loop'.
i<=randNums4.length && i>999
Here randNums4.Length is 1000 and i=0
But according to your condition, i should be greater than 999 which is not possible.

If you have go through the every post on this thread, pbrockway2 explain the same thing you are talking about.

Code:

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result += BANK_ID+"-"+lastName.charAt(0)+firstName.charAt(0)+"-"+randNums4[i]+"-"+Character.toUpperCase(lastName.charAt(1))+Charac ter.toUpperCase(firstName.charAt(1))+"-"+randNums8[i];

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Try replacing i with i-1 in the above statement

Code:

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result += BANK_ID+"-"+lastName.charAt(0)+firstName.charAt(0)+"-"+randNums4[i-1]+"-"+Character.toUpperCase(lastName.charAt(1))+Charac ter.toUpperCase(firstName.charAt(1))+"-"+randNums8[i-1];

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Quote:

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Originally Posted by kbindumadhavi

Code:

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result += BANK_ID+"-"+lastName.charAt(0)+firstName.charAt(0)+"-"+randNums4[i]+"-"+Character.toUpperCase(lastName.charAt(1))+Charac ter.toUpperCase(firstName.charAt(1))+"-"+randNums8[i];

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Try replacing i with i-1 in the above statement

Code:

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result += BANK_ID+"-"+lastName.charAt(0)+firstName.charAt(0)+"-"+randNums4[i-1]+"-"+Character.toUpperCase(lastName.charAt(1))+Charac ter.toUpperCase(firstName.charAt(1))+"-"+randNums8[i-1];

---

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Thanks! it works now that I used [i-1]

Why does [i-1] work but not [i]?

Code:

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for(i = 0;i<randNums4.length;i++)

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In the above for loop, i starts from 0 and increments by 1.
At at the point i=999, the for loop will be as follows

i=999
999<1000(randNums4.length)----> this condition satisfies
So i increments by 1 and becomes 1000

Then i=1000
1000<1000--> this is not satisfied and thus loop ends here.

So at last value of i is 1000, which started from 0.
So i=1000 will be out of length. That is if we consider even i=1000, then length becomes 1001 which is not possible
That is the reason we should replace i-1 with i