CS 40 - Lecture 18

Cover page image

Cay S. Horstmann

Lecture 17 Recap

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

A true story
I get GRE scores from a web page
I need to paste each student's scores into my spreadsheet
The formats are different
I wrote a small Java program (180 lines)
Reduces hours of drudgery to 5 minutes

Reading Plain Text

I made a TextWorld for you (download it now)
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 my 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
Submit your solution in eCampus

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

Load MyText4.java
Put it into TextWorld in the usual way
Figure out what to do for ...;
Figure out what to return
Compile and run. What is the longest word?ActiveLecture.org
Submit your solution in eCampus

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

Load MyText5.java
In Greenfoot, make a subclass in the usual way, and paste in 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 explore
What happens?
Remove duplicates: Invoke the unique method.
How many unique short words are there? ActiveLecture.org

Ok, but...

mona lisa picture

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

Did you email me your project progress report?