Java example code to generate random characters

import java.util.Random;
import java.util.UUID;

public class Dept {

	/**
	 * Generate a random string uuid
	 */
	public static String getUUID() {
		return UUID.randomUUID().toString();
	}

	/**
	 * Generate a random string uuid and replace "-" with ""
	 */
	public static String getUUNUM() {
		return UUID.randomUUID().toString().replace("-", "");
	}

	/**
	 * Generate a random number with a specified number of digits * @param n The number of digits of the generated random number */
	public static String getRandom(int n) {
		Random r = new Random();
		Long b = Math.abs(r.nextLong());
		return b.toString().substring(0, n);
	}

	public static void main(String[] args) {
		System.out.println(getUUNUM());
		System.out.println(getUUID());
		System.out.println(getRandom(6));
	}

}

//length The length of the string required by the user public static String getRandomString(int length){
   String str="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
   Random random=new Random();
   StringBuffer sb = new StringBuffer();
   for(int i=0;i<length;i++){
    int number = random.nextInt(62);
    sb.append(str.charAt(number));
   }
   return sb.toString();
 }

//You can specify the value range of a certain position in the string public static String getRandomString2(int length){
  Random random=new Random();
  StringBuffer sb = new StringBuffer();
  for(int i=0;i<length;i++){
    int number=random.nextInt(3);
    long result=0;
    switch(number){
     case 0:
       result = Math.round(Math.random()*25+65);
       sb.append(String.valueOf((char)result));
       break;
     case 1:
       result = Math.round(Math.random()*25+97);
       sb.append(String.valueOf((char)result));
       break;
     case 2:   
       sb.append(String.valueOf(new Random().nextInt(10)));
       break;
    }


   }
   return sb.toString();
 }

String filename = RandomStringUtils.randomAlphanumeric(10);