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javaasciiuppercaselowercase

Java - Method ignores Upper -> Lowercase tranformation

A question about ASCII and java: I am reading files using java, all of them containing Uppercase letters, which I am supposed to convert into lowercase, in order to treat them with another algorithm, which looks for matches between sequences read from both files. This algorithm contains this kind of comparison:

 for(int j = 0; j < pattern.length(); ++j)
        {
            //char a has a certain decimal value, so whatever char subtracted to char a
            //will be an index between 0 and 25
            int c = pattern.charAt(j) - 'a';

And the algorithm reading the files look like this: enter image description here

Anyways, whenever I read files, I get an error with the provoked by the variable text, which is supposed to have only lowercase letters. This error: ArrayIndexOutOfBoundsException caughtjava.lang.ArrayIndexOutOfBoundsException: Index -87 out of bounds for length 26

When I use a predefined String with lowercases, everything works perfectly, the only problem comes when I read the text from a file.

Is there any other way to convert uppercases into lowercases in java?

I would be very grateful if you could point out my error.

Thank you very much in advance!

Solution

  • The message from the exception is java.lang.ArrayIndexOutOfBoundsException: Index -87.

    That means that the expression pattern.charAt(j) - 'a' resulted in the value -87, which in turn means that pattern.charAt(j) must have the value 10 which is the value of '\n' - the line separator.

    It seems that your text file contains not only alphabetic characters but also at least one line separator.

    The are some possible solutions:

    • trim() the text that you have read from the file:

      text = new String(Files.readAllBytes(path)).toLowerCase().trim();

    • skip everything that is not in the range 'a' to 'z' in your algorithm:

      int c = pattern.charAt(j) - 'a';
if (c < 0 || c > 25) continue;