Foundations of Software Design Fall 2002 Marti Hearst

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Foundations of Software DesignFall 2002Marti
Hearst
Lab 7 discussion topics Casting, File I/O,
Enumeration, and Stacks John Fritch, Kaichi
Sung, Leah Zagreus    
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Type Casting

• Assigning primitive data when it would result in
  loss of precision
• (a) System.out.println(1/2)
• (b) System.out.println((float)1/2)
• Assigning an object to a subclass type
• Fish oneFish new Fish("one fish")
• stack.push(oneFish)
• Fish twoFish (Fish) stack.pop()
• System.out.println(twoFish.getColor())

Adapted from Brian Overland, Java in Plain
English 2nd ed.
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Type Casting

• Used a lot in Java because nearly all data
  structures store generic Object types.
• Stack
• Vector
• HashTable
• etc.

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Enumeration

• A convenient way to iterate through the elements
  in a data structure
• Must use type casting
• Fish charlie new Fish("pink")
• Fish freddy new Fish("yellow")
• Vector v new Vector()
• v.add(charlie)
• v.add(freddy)
• Enumeration e v.elements()
• while(e.hasMoreElements())
• Fish f (Fish) e.nextElement()
• System.out.println(f.getColor())

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File I/O

• Java uses streams for input and output
• Input streams reading data from files, user
  input, keyboard
• Output streams writing data to files, screen,
  printer
• Basic outline for File I/O
• Open the file for reading or writing
• Read or write the data
• Close the file

Adapted from Oliver Mason, Programming for Corpus
Linguistics
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Reading from a File

• Import the IO classes
• import java.io.
• To open a file for reading (1 char at a time)
• FileReader fr new FileReader("myFile.txt")
• To open a file for reading (more functionality)
• BufferedReader br new BufferedReader(new
  FileReader("myFile.txt"))
• Requires try-catch Eclipse will help

Adapted from Oliver Mason, Programming for Corpus
Linguistics
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StringTokenizer

• Break up a string into tokens separated by
  delimiters
• Words (what is the delimiter?)
• Or any substrings, separated by the delimiter of
  your choosing
• StringTokenizer st new StringTokenizer("this is
  a test")
• while (st.hasMoreTokens())
• System.out.println(st.nextToken())

Adapted from Oliver Mason, Programming for Corpus
Linguistics