File Input in Java

1
File Input in Java

• using files as input

2
Reading from a File

• A text file is used an input to the application
• Open the file
• Read and process one line at the time
• Close the file when done
• In general, the input file is formatted
• Every line has the same number of tokens
• Tokens are in the same order
• What about non-formatted files?

3
Opening an input File

• try
• FileReader textFile new FileReader(data.txt)
  
• BufferedReader inFile new BufferedReader(textFi
  le)
• System.out.println(File data.txt has been
  opened.)
• catch (FileNotFoundException fnfe)
• System.out.println(File data.txt was not
  found!)

4
Reading Line by Line

• Use the method readLine() as we did when we read
  from the Console window
• String oneLine inFile.readLine()
• Then we process the contents of oneline
• We use the StringTokenizer Class
• The readLine() method returns
• either a String object
• or the value null

5
Reading all the Lines in the File

• We need to use a loop
• String oneLine inFile.readline()
• int number
• while (oneLine ! null)
• number Integer.parseInt(oneLine)
• System.out.println(Number read is
  number)
• oneLine inFile.readLine()

6
Closing a File

• In Java, the file must be closed after we read
  the very last line.
• inFile.close()

7
Homework

• Read the following
• Chapter 19, pp. 344-347, 350-353, 359-362
• Download and read the Word document Files.doc
• Lab 6 is due Sunday the 16th