add random characters to end of string?

Question

String key = "test";

I have a key. It is 4 characters long. What i want to do is have a function which looks at the length of key and then adds random characters at the end to make it the length of 20?

So if ket was just 'te' it would add 18 random characters at the end. If key is 'test' it adds 16 random characters at the end.

??

Pick a random number generator, generate `20 - key.size()` characters and append them...? — Kerrek SB, Jun 16 '11 at 14:41
possible duplicate of [How to generate a random alpha-numeric string in Java](http://stackoverflow.com/questions/41107/how-to-generate-a-random-alpha-numeric-string-in-java) — erickson, Sep 13 '11 at 03:58

James Raitsev · Answer 1 · 2011-12-06T00:17:42.660

Consider solution as follows. In here you will get both lowercase and upper case letters mixed in.

Example:

for (int i = 0; i < 5; i++) {
    System.out.println(getRandomString("test"));
}

will return:

testRBMuWIiibcyAAaGc
testOjvmVMoQPYGJKKUs
testBnCPLyqbTUFzQrOs
testgaFkzFtnsYHNkDJR
testsisbGHzItczsJYNK

public static String getRandomString(String s) {

    int i = 0;
    int randomNumber;

    boolean isUpperCase;

    StringBuilder response = new StringBuilder();
    Random randomNumberGenerator = new Random();

    while (i++ < MAX_LENGTH - s.length()) {
        isUpperCase = randomNumberGenerator.nextBoolean();
        randomNumber = randomNumberGenerator.nextInt(26) + 65;

        response.append(isUpperCase ? (char) randomNumber : 
                      Character.toLowerCase((char) randomNumber));
    }

    return response.insert(0, s).toString();
}

score 3 · Accepted Answer · edited May 23 '17 at 11:46

3

SO isn't about making others write your code... but to give you a starting point, take a look at this question, and modify to suit.

edited May 23 '17 at 11:46

Community

1
1

answered Jun 16 '11 at 14:43

Pontus Gagge

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score 0 · Answer 3 · answered Jun 16 '11 at 15:15

A terse solution is:

Random random = new Random();
String randomString = "test";
       for(;randomString.length() < 20 ;) {
            char randomChar = (char) random.nextInt(123);
            randomString += (Character.isLetterOrDigit(randomChar)) ? randomChar : ""; 
        }

score -1 · Answer 4 · answered Jun 16 '11 at 14:48

-1

if(password.length() != 20){
                while (password.length() != 20){
                    password += (char)String.valueOf(myRandom.nextInt()).charAt(0); 
                }
            }

answered Jun 16 '11 at 14:48

Beginner

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add random characters to end of string?

4 Answers4