add random value on sepecific field selenium webdriver

I'm pretty new to Selenium and Java just wanted to know if there's way I can randomly add a value in a specific field, lets say in "Case ID" field I want to generate a random 8 alphanumeric value, below is the xpath of the field I'm referring to:

driver.findElements(By.xpath(".//*[@id='case_id']")).size() != 0) {

Thanks in Advance, P