CODEWITHSUNDEEP
javastringrandomstringbuilder
Jude Niroshan
Jude Niroshan

Reputation: 4460

Generate a String for a given size

How can I generate a String of a given size?

int someLimit = GlobalLimits.BULK_SIZE;

I want 3 Strings which satisfy the below conditions.

- RandomStr.length < someLimit.length

- RandomStr.length = someLimit.length

- RandomStr.length > someLimit.length

This is what I have tried so far.

private String getLowerRandomString(int upto){
  StringBuilder sBuilder = new StringBuilder();
  for (int i = 0; i < upto; i++){
    sBuilder.append("A");
  }

  return sBuilder.toString();
}

The problem what I see is, if my limit = 10000, it still loop up-to 9999 which is unnecessary. Share if you know a better approach than this. Thank you.

FYI: I was writing a unit test for a simple helper method. 

public boolean isBulk(String text){
 int bulkLimit = ImportToolkit.getSizeLimit();
 if (text != null && text.length() > bulkLimit){
  return true;
 }
 return false;
}

So, I want to pass different sizes of strings as parameters to this method and want to assert whether it gives me expected results.

Upvotes: 4

Views: 8140

Answers (6)

Jefferson Lima
Jefferson Lima

Reputation: 5436

If you're only concerned about the string's length, you can just do this:

String str = new String(new char[SIZE]);

This is useful, for example, when you want to test if a given method fails when it is given a string of a specific length.

Upvotes: 2

notionquest
notionquest

Reputation: 39226

Please refer the link which has the secure way to create random string for any specified length. I have used it in my project and it worked fine.

Upvotes: 0

Sid
Sid

Reputation: 491

Take a look at Xeger library here . Your code would go like this.

    public static void main(String[] args){


 String regex="([0-9]{100})";     
    System.out.println(new Xeger(regex).generate());

}

Output :- 5262521775458685393102235626265923114201782357574146361524512101753254114567366125627554628148696482

You can change 100 or 1000 according to your need.

Jar Location here.

-Sid

Upvotes: 1

Nicktar
Nicktar

Reputation: 5575

What about using apache commons? It has a RandomStringUtils class that provides exactly the functionality you're looking for, but in the end it loops too...

org.apache.commons.lang3.RandomStringUtils#randomAlphanumeric(int count)

From JavaDoc

Creates a random string whose length is the number of characters specified.

Characters will be chosen from the set of alpha-numeric characters.

Parameters:
    count - the length of random string to create
Returns:
    the random string

If it doesn't need to be random there is another, cheaper method in Stringutils:

org.apache.commons.lang3.StringUtils#repeat(char, int)

But in the end it too loops...

From JavaDoc

Returns padding using the specified delimiter repeated to a given length.

 StringUtils.repeat('e', 0)  = ""
 StringUtils.repeat('e', 3)  = "eee"
 StringUtils.repeat('e', -2) = ""


Note: this method doesn't not support padding with Unicode Supplementary Characters as they require a pair of chars to be represented. If you are needing to support full I18N of your applications consider using repeat(String, int) instead.

Parameters:
    ch - character to repeat
    repeat - number of times to repeat char, negative treated as zero
Returns:
    String with repeated character
See Also:
    repeat(String, int)

Upvotes: 4

Gaurava Agarwal
Gaurava Agarwal

Reputation: 984

Use Random to generate a number less than Limit and greater than limit and pass to function to generate a string of that length

       lowerLimit= 0 + (int)(Math.random() * maximum); 
       higherLimit= minimum + (int)(Math.random() * maximum);
       smallerString= getLowerRandomString(lowerLimit);
       greaterString= getLowerRandomString(higherLimit);

For help on limiting random number, please check this post.How do I generate random integers within a specific range in Java?

Upvotes: 0

JP Bose
JP Bose

Reputation: 22

If you only concern about the string length, Do a mathematical operation that result a big value. Convert that result value as string and perform your validation. If you do not want numeric then, instead of appending single string 'a' to stringBuilder. Append a big string and in your for loop increment based on the length of the string that you append to string builder.

Upvotes: 0

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