To Lecture Notes

IT 313 -- Jan 28, 2020

Review Exercises

1. How do you do the following in an IntelliJ project?
   
   1. Add a new class?
      Ans: Right click on the src file and select New >> Class.  Enter the class name and click OK.
   2. Add a new file?
      Ans: Depending on where you want to place the new file, right click on the project name or on the src file. Select New >> File; enter the new file name.
   3. Read from the file in b?
      Ans: Use these statements:
      

      File f = new File("input.txt");
      Scanner s = new Scanner(f);
      String line = s1.nextLine( );
      

      If the input file is in a module, for example module1, in the src folder, use this statement to create the file:
      

      File f = new File("input.txt");
      

   4. Write to an output file? Ans:
      

      PrintWriter pw = new PrintWriter("output.txt");
      pw.println("Test output.");
      pw.close( );
      

2. This main method is supposed to load the values from a file into a double array, then compute the average of the values in this array, writing the average to an output file. Reorder the lines of this main method to accomplish this:
   Here are the contents of the numbers.txt file:
   

   34,21,78,60,53,21,9
   

   Ans: the reordered lines are shown below the original scrambled main method.
3. Refactor the main method in Exercise 1 by extracting two methods: loadValuesFromFile that returns an array of int, and computeAverage that returns the average of the value in the array of int.
   Ans: Look below the reordered lines.
4. Given the classes B and Main, draw the variable trace table and predict the output.
   Ans: The variable trace table and output are shown below the classes.

Reading Data from the Web

• We know how to use a Scanner to read from the keyboard or from an input file; we can also use a Scanner to read from a string.
  See the StringTest class in the InputOutput Example project.
• See can also use a Scanner object to read from the web.
• Look at the ReadFromWeb class in the InputOutput Example project.
• The ReadFromWeb class reads from this website:
  http://facweb.cdm.depaul.edu/sjost/it313/greeting.htm
• To read from the web:
  

  InputStream s = new URL(urlString).openStream( );
  Scanner in = new Scanner(s);
  while (in.hasNextLine( )) {
      String line = in.nextLine( );
      // Process line
  }
  in.close( );

Project 4

• This section will be discussed on Thursday, Jan 30.
• Look at the Project 4 Description.
• Use the String object chars and String array codes to translate an input string into Morse code:
  

  String chars = " ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
  String[ ] codes = {"   ", ".-", "-...", "-.-.", "-..", 
      ".", "..-.", "--.", "....", "..", ".---", "-.-", 
      ".-..", "--", "-.", "---", ".--.", "--.-", ".-.", 
      "...", "-", "..-", "...-", ".--", "-..-", "-.--", 
      "--..", ".----", "..---", "...--", "....-", ".....", 
      "-....", "--...", "---..", "----.", "-----"};
  

  Write a method named toMorseCode to perform the translation.
  Ans: Here are the source code files.

Using a FileChooser

• This section will be discussed on Thursday, Jan 30.
• Look at the UseFileChooser class in the InputOutput Example.

ArrayLists

• Declare and instantiate an ArrayList object a. Add these items to a:
  

  37  3.452  "dog"  'c'  true.
  

• Look up the ArrayList collection in the Java Class Library and find some useful methods to test.
  Ans: We tested these ArrayList methods:
  

  add  size  get  contains  toString  clear
  

  Here is the test source code for these methods.

Additional Examples

• Look at the dice1 example in the Loops Example project.