File I/O - Absolute Java - page 603

Self-Test Exercises (continued)

15. One difference between the try blocks in Display 10.1 and Display 10.7 is
that the try block in Display 10.1 encloses only the opening of the fi le, while
the try block in Display 10.7 encloses most of the action in the program. Why
is the try block in Display 10.7 larger than the one in Display 10.1 ?

16. Might the following throw an exception that needs to be caught or declared in
a throws clause?

BufferedReader inputStream =
new BufferedReader( new FileReader("morestuff2.txt"));
(The stream inputStream would be used to read from the text fi le
morestuff2.txt .)

TIP: Reading Numbers with BufferedReader

Unlike the Scanner class, the class BufferedReader has no methods to read a
number from a text file. You must write your code to read the number as a string
and convert the string to a value of a numeric type, such as int or double . To read
a single number on a line by itself, read it using the method readLine , and then use
Integer.parseInt , Double.parseDouble , or some similar method to convert the
string read to a number. If there are multiple numbers on a single line, read the line
using readLine and then use the StringTokenizer class to decompose the string
into tokens. Next, use Integer.parseInt or a similar method to convert each token
to a number.
Integer.parseInt, Double.parseDouble , and similar methods that convert
strings to numbers are explained in Chapter 5 in the subsection entitled “Wrapper
Classes.” The StringTokenizer class is discussed in Chapter 4 in the starred subsec-
tion entitled “The StringTokenizer Class”.

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Testing for the End of a Text File with BufferedReader
When using the class BufferedReader , if your program tries to read beyond the end
of the file with either of the methods readLine or read , then the method returns a
special value to signal that the end of the file has been reached. When readLine tries
to read beyond the end of a file, it returns the value null . Thus, your program can
test for the end of the file by testing to see if readLine returns null . This technique
is illustrated in Display 10.9 . When the method read tries to read beyond the end of
a file, it returns the value -1 . Because the int value corresponding to each ordinary
character is positive, this can be used to test for the end of a file.