String generator in Java

Question

I need to generate random alphanumeric string (5 or 6 char) in order to put it to specific field. Could anyone pls provide me solution ? Have tried several methods described in another posts on stack but without success.

Have tried something like that:

public static String generateString(Random rng, String characters, int length)
{
    char[] text = new char[length];
    for (int i = 0; i < length; i++)
    {
        text[i] = characters.charAt(rng.nextInt(characters.length()));
    }
    return new String(text);
}

but no idea why random is passed as an argument and what should I provide for it while calling method

_Have tried several methods_ Can you pease post your attempts, and tell us what didn't work, why, what you expected and what is happening instead? — BackSlash, Sep 15 '15 at 07:50

score 2 · Accepted Answer · answered Sep 15 '15 at 07:55

2

Since you attempted many as you stated, I can help you with one of the easiest solutions-

Have a string declared with characters of your choice. e.g. 0..9..a..z..A..Z

Have a loop with the number of characters you would like to generate. e.g. if you want 5 random characters, you would have something like for(int i = 0; i < 5; i++)

For each iteration, pick a random character from step 1 using the length of the string you have in step 1.

answered Sep 15 '15 at 07:55

Sajal Dutta

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yes just write every character manually. Only with alphanumeric ones your have 62 characters to write and you can forget one... – Erwan C. Sep 15 '15 at 08:08

score 1 · Answer 2 · answered Sep 15 '15 at 08:02

Here is a sample code:

private static final char[] VALID_CHARACTERS =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456879".toCharArray();

public static String getRandomString( final int length ) {
    // Check input
    if( length <= 0 ) {
        return "";
    }
    // Generate string
    Random rand = new Random();
    char[] buffer = new char[length];
    for( int i = 0; i < length; ++i ) {
        buffer[i] = VALID_CHARACTERS[rand.nextInt( VALID_CHARACTERS.length )];
    }
    //
    return new String( buffer );
}

This simple method uses a constant of valid characters, polling randomly a character per time from it to build the string of the desired length.

For example, to get an alphanumeric string of 10 characters, you call the method this way:

getRandomString( 10 );

String generator in Java

2 Answers2