Random string consists of random characters.

 
import java.util.Random;

public class Main {
  public static void main(String[] argv) {
    System.out.println(randomString(10));
  }

  public static String randomString(int length) {
    StringBuilder b = new StringBuilder();
    for (int i = 0; i < length; i++) {
      b.append(base.charAt(random.nextInt(base.length())));
    }
    return b.toString();
  }

  private static String base = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabsdefghijklmnopqrstuvwxyz";
  private static Random random = new Random();
}
  

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