Java random number with given length [duplicate]

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To generate a 6-digit number:

Use Random and nextInt as follows:

Random rnd = new Random();
int n = 100000 + rnd.nextInt(900000);

Note that n will never be 7 digits (1000000) since nextInt(900000) can at most return 899999.

So how do I randomize the last 5 chars that can be either A-Z or 0-9?

Here’s a simple solution:

// Generate random id, for example 283952-V8M32
char[] chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".toCharArray();
Random rnd = new Random();
StringBuilder sb = new StringBuilder((100000 + rnd.nextInt(900000)) + "-");
for (int i = 0; i < 5; i++)
    sb.append(chars[rnd.nextInt(chars.length)]);

return sb.toString();

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