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In this example, we will learn how to generate random strings and alphanumeric random strings in Java.
import java.util.Random;
class Main {
public static void main(String[] args) {
//Create a string containing all A-String of Z characters
String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
//Create a random string generator
StringBuilder sb = new StringBuilder();
//Create an object of the Random class
Random random = new Random();
//Specify the length of the random string
int length = 7;
for(int i = 0; i < length;++) {
//Generate a random index number
int index = random.nextInt(alphabet.length());
//Get the character specified by index index
//From the string
char randomChar = alphabet.charAt(index);
//Attach the character to the string generator
sb.append(randomChar);
}
String randomString = sb.toString();
System.out.println("The randomly generated string is: " + randomString);
}
}Output Result
Random string is: IIYOBRK
In the above example, we first created a string containing all the letters. Next, we used the Random class's nextInt() method to generate a random index number.
Using a random index number, we generated a random character from the string letters. Then, we used the StringBuilder class to concatenate all characters together.
If you want to change the random string to lowercase, you can use the String's toLowerCase() method.
randomString.toLowerCase()
Note：The output will be different each time you run the program.
import java.util.Random;
class Main {
public static void main(String[] args) {
// Create a string composed of uppercase and lowercase letters and numbers
String upperAlphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
String lowerAlphabet = "abcdefghijklmnopqrstuvwxyz";
String numbers = "0123456789";
//Merge all strings
String alphaNumeric = upperAlphabet + lowerAlphabet + numbers;
//Create a random string generator
StringBuilder sb = new StringBuilder();
//Create an object of the Random class
Random random = new Random();
//Specify the length of the random string
int length = 10;
for(int i = 0; i < length;++) {
//Generate a random index number
int index = random.nextInt(alphaNumeric.length());
// Get the character at index index from the string
char randomChar = alphaNumeric.charAt(index);
// Append the character to the string builder
sb.append(randomChar);
}
String randomString = sb.toString();
System.out.println("The randomly generated string is: " + randomString);
}
}Output Result
The randomly generated string is: pxg1Uzz9Ju
Here, we created a string that contains the characters from0 to9thenumbers as well as uppercase and lowercase letters.
From the string, we randomly generated a string of length10alphanumeric string.