Exercise 9A

1. It reads a single line of text from br into a string variable. The line contains the author's name, the document's title, and the number of copies, separated by ';'. The following is an example of a line formatted in such a way:
   Bruce Tate;Beyond Java;53

2. It extracts the information from the string using the split() method of the class String.
3. It constructs a new Document object using the information extracted from the line of text, and returns it.

Solution

Exercise 9B

Implement a client of the class Document that reads a set of Document objects from a given input file, computes the average number of copies, and writes to and output file all those documents whose number of copies is greater than the average.

More precisely, the client application should do the following:

1. It reads from the command line the name of an input file and the name of an output file. The input file should contain in the first line an integer numDocs, and in the next numDocs lines the information about documents, one document per line, formatted according to part A of the exercise.
2. It reads from the first line of the input file the number numDocs of documents, and creates an array of Document objects of size numDocs.
3. Using the method read(), it reads from the remaining lines of the input file the Document objects and stores them into the array.
4. Based on the documents stored in the array, it computes the average number of copies.
5. It writes to the output file all documents whose number of copies is greater than the average. The first line of the file should again contain the number of documents stored in the file, and all remaining lines of the file should be formatted in the same way as for the input file.

Solution

Exercise 9C

Adapt the client application to catch the following exceptions:

• FileNotFoundException. The message "The file does not exist" should be displayed.
• IOException. The message "The file cannot be read" should be displayed.
• NumberFormatException. Occurs when an input file is not formatted correctly, i.e. the first line does not contain an integer representing the number of documents, or an integer representing the number of copies of a document is not present in the required position in a line containing the info for a document. The message "Incorrect formatting: the number of documents or the number of copies is missing" should be displayed

Solution

Exercise 9D

Define a class DocumentFormatException to represent document formatting exceptions. Extend the method read() of the class Document so that it throws this exception in the following two cases:

• The name of the author, the title of the document, or the number of copies is missing. This can be checked using the size of the array obtained by executing the split method. The correct size of the array is 3.
• The number of copies in the input line is not an integer. This can be checked by catching NumberFormatException while converting a string into an integer.

Also, modify the client application to catch DocumentFormatException. If the exception occurs the client application should do the following:

1. It displays the notification message including the index of the badly formatted line.
2. It sets the corresponding element of the array of Documents to null. Afterwards, while calculating the average number of copies and writing to the output file, it skips all elements of the array whose value is equal to null.

Solution