How to generate a random String in Java [duplicate]

Question

I have an object called Student, and it has studentName, studentId, studentAddress, etc. For the studentId, I have to generate random string consist of seven numeric charaters, eg.

studentId = getRandomId(); studentId = "1234567" <-- from the random generator. 

And I have to make sure that there is no duplicate id.

Answer 1

Generating a random string of characters is easy - just use java.util.Random and a string containing all the characters you want to be available, e.g.

public static String generateString(Random rng, String characters, int length) {     char[] text = new char[length];     for (int i = 0; i < length; i++)     {         text[i] = characters.charAt(rng.nextInt(characters.length()));     }     return new String(text); } 

Now, for uniqueness you'll need to store the generated strings somewhere. How you do that will really depend on the rest of your application.