Java ArrayList Primer Tutorial

Java XCode ArrayList Primer Tutorial

Here is a tutorial that uses ArrayList structure in Java via XCode on a Mac laptop.

This program counts the occurrence of characters within the contents of a text file.

We have one input text file which we are going to read.
We use one ArrayList to contain characters of interest to find.
We use another ArrayList to contain character counts collected.

Breaking this down, it would be good to:

a) have method that reads the text file and does the report
b) have method to count occurrences of a character within a String
c) have method to count number of words within a String (and total characters in words)

This way you can report:

. occurrences of a character of interest within a line of the input text file
. total count and percentage of characters of interest within the whole text file
. total count and percentage of other characters within the whole text file
. total count of words within the whole text file
. average word size is ((total characters in words) / (total count of words))

So we’ll build up a FindOccurrences class this way.

Need to have rules about the input text file. Will have it that:

1) there is an optional first header record with number of records of interest
2) all records need {cr} (and/or {lf}) delimitation (as a text file should)

How do we obtain the filename? Will have it that:

(1) it can optionally be passed as a command line parameter
(2) if not we will prompt for it and allow a non-answer meaning it is inputfile.txt

Do we assume a and A (for instance) are the same thing? Will have it that:

(a) assume as a default a and A are to be treated as one entity for searching purposes
(b) there is a, albeit awkward, way to say that a and A are separate, via (2) above

Let’s see some Java programming code for this, and how it works …

Download source code and rename to FindOccurrences.java

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