Given a size as n, The task is to generate a random alphanumeric String of this size. Below are various ways to generate random alphanumeric String of given size: Prerequisite : Generating random numbers in Java
- Method 1: Using Math.random() Here the function getAlphaNumericString(n) generates a random number of length a string. This number is an index of a Character and this Character is appended in temporary local variable sb. In the end sb is returned.
JAVA
// Java program generate a random AlphaNumeric String // using Math.random() method public class RandomString { // function to generate a random string of length n static String getAlphaNumericString(int n) { // choose a Character random from this String String AlphaNumericString = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" + "0123456789" + "abcdefghijklmnopqrstuvxyz"; // create StringBuffer size of AlphaNumericString StringBuilder sb = new StringBuilder(n); for (int i = 0; i < n; i++) { // generate a random number between // 0 to AlphaNumericString variable length int index = (int)(AlphaNumericString.length() * Math.random()); // add Character one by one in end of sb sb.append(AlphaNumericString .charAt(index)); } return sb.toString(); } public static void main(String[] args) { // Get the size n int n = 20; // Get and display the alphanumeric string System.out.println(RandomString .getAlphaNumericString(n)); } } |
Output:
kU9vRVm9T1lFMbi3duO1
- Method 2: Using CharSet Generate 20 character long alphanumeric string randomly using Charset which is in java.nio.charset package.
- First take char between 0 to 256 and traverse.
- Check char is alphabetic or numeric.
- If yes, then add at the end of our String
- Return String
- Method 3: Using Regular Expressions
- First take char between 0 to 256.
- remove all char except 0-9, a-z and A-Z.
- Random select an char
- Add at the end our required variable
- Method 4: Generating random String of UpperCaseLetter/LowerCaseLetter/Numbers When some specific characters are needed in the alphanumeric string, like only the UpperCaseLetter or LowerCaseLetter or Numbers, use this method. Below example generates a random String of LowerCase letters of size n. Below is the implementation of the above approach:
JAVA
// Java program generate a random AlphaNumeric String // using CharSet method import java.util.*; import java.nio.charset.*; class RandomString { static String getAlphaNumericString(int n) { // length is bounded by 256 Character byte[] array = new byte[256]; new Random().nextBytes(array); String randomString = new String(array, Charset.forName("UTF-8")); // Create a StringBuffer to store the result StringBuffer r = new StringBuffer(); // Append first 20 alphanumeric characters // from the generated random String into the result for (int k = 0; k < randomString.length(); k++) { char ch = randomString.charAt(k); if (((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9')) && (n > 0)) { r.append(ch); n--; } } // return the resultant string return r.toString(); } public static void main(String[] args) { // size of random alphanumeric string int n = 20; // Get and display the alphanumeric string System.out.println(getAlphaNumericString(n)); } } |
Output:
qbhalyuzrenuwgvqidno
Time complexity: O(n) where n is size of string to be generated
Auxiliary space: O(n) for StringBuffer
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