Generate random String of given size in Java
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.
- 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:
Time complexity: O(n) where n is size of string to be generated
Auxiliary space: O(n) for StringBuffer