Answer by cwtuan for How to generate a random alpha-numeric string

Given the some characters (AllCharacters), you could pickup a character in the string randomly. Then use-for loop to get random charcter repeatedly.

public class MyProgram {  static String getRandomString(int size) {      String AllCharacters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";      StringBuilder sb = new StringBuilder(size);      int length = AllCharacters.length();      for (int i = 0; i < size; i++) {          sb.append(AllCharacters.charAt((int)(length * Math.random())));      }      return sb.toString();  }  public static void main(String[] args) {      System.out.println(MyProgram.getRandomString(30));  }}

• Try it on the sandbox
• Also see other languages implement random string generator