CS 40 - Lecture 18

David S. Taylor

Lecture 17 Recap

• Privacy Issues
• 100+ years ago: technology already threatened privacy.
• The threat has greatly accelerated in the last 10-15 years
• Do you care? (Different generations have different attitudes.)

Lecture 16 Recap (back to the technical stuff)

• Edge detection: If pixel color differs by a large amount from neighboring pixels, color black, otherwise, color white
• Mirroring: Find distance from mirror line, then go the same distance in the other direction
• Processing image parts: Check whether x- or y-value is > (i.e. to the right or bottom of) a line, or < (i.e. to the left or top of) a line

Plain Text

• Letters, numbers, special symbols
• No fonts, no colors, one size, no bold, no italic
• Commonly generated from scraping spreadsheets, word processors, emails, web pages (i.e. copy and paste into Notepad)
• Easy to process

Example: Office Automation

Example: Office Automation

• Need GRE scores from a web page
• Need to paste each student's scores into my spreadsheet
• The formats are different
• A small Java program (180 lines) reduces hours of drudgery to 5 minutes

Reading Plain Text

• TextWorld for you (download it now)
• Unzip it
• Choose it as a scenario in Greenfoot
• Very similar to PictureWorld
• Very similar to Scanner class in standard Java library, but you need not worry about “exceptions”
• If you ever have to do this kind of work, either use these classes or rewrite code to use Scanner

Loop Through Words

public class MyText2 extends Text
{
  public int countWords()
  {
    int count = 0;
    for (String word : getWords())
    {
      count++;
    }
    return count;
  }
}

Lab 1: Running the Program

• Make a subclass MyText2 of Text
• Edit the code as shown on the previous slide
• Click on Compile
• Right-click on MyText2
• Select new MyText2() and drag into white square
• Right-click on text icon and select pick from the Text superclass
• Pick alice30.txt
• Right-click on the text icon and select countWords
• What happens? ActiveLecture.org

Analyzing Plain Text

• Loop through words:

  for (String word : getWords())

• Or loop through lines:

  for (String line : getLines())

• Or loop through numbers (skipping everything that isn't a number)

  for (double x : getNumbers())

Counting

• If some criterion is fulfilled, increment counter
• Example: How many the are in Alice in Wonderland?

• if (word.equals("the"))
  {
     ...
  }

• Other criteria:

  if (word.length() <= 3) { ... }
  if (word.startsWith("th")) { ... }
  if (word.endsWith("th")) { ... }
  if (word.contains("th")) { ... }

Lab 2: Count the "the"s

• In Greenfoot, form subclass MyText3
• Copy/paste/edit countWords → countThes
• Try it out. How many the are in Alice in Wonderland? ActiveLecture.org
• What if we want both the and The (and any other variants)? (Try using equalsIgnoreCase instead of equals.) ActiveLecture.org
• Submit your code to Google Groups

Finding

• Find a string that fulfills a criterion
• Change return type from int to String. Example:

  String longestWord()

• To find longest word, keep track of longestWordSoFar
• Replace if current word longer

  String longestWordSoFar = "";
  for (String word : getWords())
  {
     if (word.length() > longestWordSoFar().length())
     {
        ...;
     }
  }

Lab 3: The Longest Word in Alice

• Edit the MyText4 class
• Figure out what to do for ...;
• Figure out what to return
• Compile and run. What is the longest word?ActiveLecture.org
• Submit your code to Google Groups

Collecting

• Collect all words that fulfill a criterion
• Change return type from int to WordList
• Every time you find a match, call add

  WordList shortWords()
  {
     WordList list = new WordList();
     for (String word : getWords())
     {
        if (word.length() < 3)
        {
           list.add(words);
        }
     }
     return list;
  }

Lab 4: Short Words in Alice

• Consider MyText5
• Open it up, and look at the code.
• Make an instance of MyText5 and drag it into the world.
• Right-click, then select act
• A dialog will appear (because act calls pick). Pick alice30.txt
• A list icon will appear next to the text icon
• Right-click on that and click Inspect
• Click Inspect on the dialog
• You should see a count of the short words now
• Click Inspect in that dialog.
• What do you see now?
• Close dialogs
• Remove duplicates: Invoke the unique method on the list.
• How many unique short words are there? ActiveLecture.org

Ok, but...

• There is a problem with the longestWord method.
• What if there are several words with the same length?
• First find a word of maximum length by calling longestWord
• Figure out its length
• Collect all words of that length

  WordList collectWordsOfLength(int n)

• Which words do you get? ActiveLecture.org

Reminders

• Email a second project progress report this week.