exercise No. 168

Adding line numbers to text files Create comment in forum


We want to add line numbers to arbitrary text files not necessarily being related to programming. Consider the following HTML example input:

        <title>A simple HTML example</title>
        <p>Some text ... </p>

Your application shall add line numbers:

1: <html>
2:     <head>
3:         <title>A simple HTML example</title>
4:     </head>
5:     <body>
6:         <p>Some text ... </p>
7:     </body>
8: </html>


  1. Given the name of an existing file you may create an instance of BufferedReader:

    final FileReader fileReader = new FileReader(inputFileName);
    final BufferedReader inputBufferedReader = new BufferedReader(fileReader);
  2. You will have to deal with possible FileNotFoundException problems providing meaningful error messages.

  3. The BufferedReader class provides a method readLine() allowing to access a given file's content line by line.


    Even if a file exists you have my encounter IOException problems being related to i.e. missing permissions.


This solutions reacts both to inexistent files and general IO problems:

File not found: Testdata/input.java

Two test cases deal both with readable and non-existing files: and expected exceptions:

public void testReadFileOk() throws FileNotFoundException, IOException {
  ReadFile.openStream("Testdata/input.txt"); // Existing file
@Test (expected=FileNotFoundException.class) // We expect this exception to be
                                             // thrown.
public void testReadMissingFile() throws FileNotFoundException, IOException {
  ReadFile.openStream("Testdata/input.java"); // Does not exist

Notice the second test which will only succeed if a FileNotFoundException is being thrown.

exercise No. 169

A partial implementation of GNU UNIX wc Create comment in forum


In this exercise we will partly implement the (Gnu) UNIX command line tool wc (word count). Prior to starting this exercise you may want to:

  • Execute wc for sample text files like e.g. a Java source file of similar:

    goik >wc BoundedIntegerStore.java
      58  198 1341 BoundedIntegerStore.java

    What do these three numbers 58, 198 and 1341 mean? Execute wc --help or man wc or read the HTML documentation.

  • wc may process several file in parallel thereby producing an extra line ❶ summing up all values:

    goik >wc bibliography.xml swd1.xml
        69     83   2087 bibliography.xml
      6809  18252 248894 swd1.xml
      6878  18335 250981 total 
  • wc can be used in pipes () like:

    goik >grep int BoundedIntegerStore.java | wc
         12      76     516

    The above output 12 76 516 tells us that our file BoundedIntegerStore.java does have 12 lines containing the string int.

A partial implementation shall offer all features being mentioned in the introduction. The following steps are a proposal for your implementation:

  1. Write a method counting the number of words within a given string. We assume words to be separated by at least one white space character (space or \t). Write some tests to assure correct behaviour.

  2. Read input either from a list of files or from standard input depending on the number of arguments to main(String[] args):

    • If args.length == 0 assume to read from standard input.

    • if 0 < args.length try to interpret the arguments as filenames.

  3. Write a class TextFileStatistics being able to and count characters, words and lines of a single input file. Instances of this class may be initialized from a BufferedReader.

    Write corresponding tests.

  4. You may create an instance of BufferedReader from System.in via:

    new BufferedReader(new InputStreamReader(System.in))
  5. Create an executable Jar archive and execute some examples. The UNIX command cat writes a file's content to standard output. This output may be piped as input to your application as in cat filename.txt | java -jar .../wc-1.0.jar.


Executing mvn package creates an executable Jar file ../target/wc-1.0.jar. We test both ways of operation:

Reading from standard input
goik >cat Testdata/input.html | java -jar target/wc-1.0.jar
  9    14    137
Passing file names as parameters
goik >java -jar target/wc-1.0.jar Testdata/*
  9    14    137  Testdata/input.html
  4     5     41  Testdata/model.css
 13    19    178  total

Junit tests of internal functionality:

Counting words in a given string:
public void testNoWord() {
  Assert.assertEquals("Just white space", 0,
       TextFileStatistics.findNoOfWords(" \t"));

public void testSingleWord() {
  final String s = "We're";
  Assert.assertEquals("text='" + s + "'", 1,

public void testTwoWords() {
  final String s = "We are";
  Assert.assertEquals("text='" + s + "'", 2,

public void testWordsWhiteHead() {
  final String s = "\t \tBegin_space";
  Assert.assertEquals("text='" + s + "'", 1,

public void testWordsWhiteTail() {
  final String s = "End_space \t ";
  Assert.assertEquals("text='" + s + "'", 1,

public void testWhiteMulti() {
  final String s = "    some\t\tinterspersed   \t  spaces \t\t ";
  Assert.assertEquals("text='" + s + "'", 3,
Analyzing test file data:
public void testTwoInputFiles() throws FileNotFoundException, IOException {

  final String model_css_filename =
    "Testdata/model.css",      //  4 lines   5  words  41 character
      input_html_filename =
    "Testdata/input.html";     //  9 lines  14  words 137 character
                               // total 13 lines  19  words 178 character

  final TextFileStatistics
    model_css = new TextFileStatistics(
      new BufferedReader(new FileReader(model_css_filename)),

    input_html = new TextFileStatistics(new BufferedReader(
        new FileReader(input_html_filename)), input_html_filename);

  // File Testdata/model.css
  Assert.assertEquals( 4, model_css.numLines);
  Assert.assertEquals( 5, model_css.numWords);
  Assert.assertEquals(41, model_css.numCharacters);

  // File Testdata/input.html
  Assert.assertEquals(  9, input_html.numLines);
  Assert.assertEquals( 14, input_html.numWords);
  Assert.assertEquals(137, input_html.numCharacters);

  // Grand total
  Assert.assertEquals( 13, TextFileStatistics.getTotalNumLines());
  Assert.assertEquals( 19, TextFileStatistics.getTotalNumWords());
  Assert.assertEquals(178, TextFileStatistics.getTotalNumCharacters());