CODEWITHSUNDEEP
javastring
shubham salunke
shubham salunke

Reputation: 505

Maximum length of a String in Java

I am new to Java and I was wondering if there was a way in which I can limit the number of characters entered in a String?

I have to create an application for a school project in which I need to use files for storing data and my class has various string variables and since I need to use the seek method of the RandomAccessFile class, and also to read only one object at a time from the file, I need all objects to have the same size, so is it possible?

Upvotes: 0

Views: 2850

Answers (3)

DwB
DwB

Reputation: 38328

The description of your class project sounds like you need or want to use a fixed length record structure. These are not nicely supported in Java.

If you have one field in your record, then just use a solution similar to that described in the Julian answer. Instead of worrying about short fields, just append spaces at the end and trim to field length.

If you have multiple fields in your record then you will want to do something like this:

  1. Create a class that has a field for each field in your record. String is the most likely type for each field.

  2. Add a method to the class (mentioned in #1) to build the fixed length record. This method will do the following for each field in the fixed length record:

    1. Add spaces to the end of each String (add as many spaces are the field size)
    2. Get the byte array from the string that contains the value for the current field in the fixed length record.
    3. Copy the bytes into the correct location in the fixed record buffer. Since you added spaces in #1 above, there is no need to pad the field. Just trim it to the field length.

This assumes that all fields are left justified and space filled.

Upvotes: 0

Julian
Julian

Reputation: 96

You cannot limit the number of characters in a String. I think, in your usecase, the best solution would be to trim the string to the maximum size.
For Example:

String input = "123456789";
String result = input.substring(0, 4);
//result is: "1234"

To ensure that you do not receive an IndexOutOfBoundsException when the input string is less than the expected length do the following instead:

input.substring(0, Math.min(MAX_CHAR, input.length()));

Math.min() will return the minimum of the two parameters.

Upvotes: 2

bvdb
bvdb

Reputation: 24770

When reading data from a file, it would make sense to read your data as a byte[], which obviously has a fixed size.

Converting a byte[] to a String is as easy as new String(bytes, StandardCharsets.UTF8) or any other encoding.

That being said, you could make the encoding configurable in your application, or use the system-default. In that case, you can just new String(bytes) to convert them.

You should be aware though that the size of a String does not always match its size in bytes. In fact for a simple encoding such as US_ASCII or ISO_8859_1 (=Latin1) it's just 1 byte per character. However, an encoding like UTF-8 supports more characters, and will sometimes need multiple bytes to store a single character.

That challenge of encodings and their variable character-size has been around for ages and is the reason why databases have a variety of different datatypes for strings (e.g. VARCHAR vs NVARCHAR).

Upvotes: 0

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