Chapter 9 1

Chapter 9 – Part 2

Overview of Streams and File I/O Text File I/O Binary File I/O File Objects and File Names

Streams and File I/O

Chapter 9 2

*Special Note: Using Path Names

Path name—filename and the full directory to the file Relative path name—path below the directory

containing the running program UNIX/Linux path name:/user/smith/home.work/java/FileClassDemo.java Windows path name:D:\Work\Java\Programs\FileClassDemo.java to use a backslash ( \ ) in a quoted string, it is preceeded

by another backslash"D:\\Work\\Java\\Programs\\FileClassDemo.java" Java accepts path names in UNIX/Linux or Windows

format, regardless of current OS

Chapter 9 3

Reading Words in a String:Using StringTokenizer Class

there are BufferedReader methods to read a line string or a single character, but not just a single word

the StringTokenizer class can be used to parse a line into individual words» load the library: java.util.*» its useful methods (page 564-565)

– .countTokens(), .nextToken(), .hasMoreTokens()

» two constructors exist that define how the input string is delimited; delimiter-the character used for separation

– default delimiter is "white space" (space, tab, newline)

» tokenizing a string can be used in many situations

Chapter 9 4

Example: StringTokenizer

display the words separated by the following chars: space, newline ( \n ), period ( . ), or comma ( , ).

String inputLine = SavitchIn.readLine();

// wordFinder will hold the tokenized listStringTokenizer wordFinder = new StringTokenizer( inputLine, " \n.," );

while ( wordFinder.hasMoreTokens() ){ System.out.println( wordFinder.nextToken() );}

Question2bor!tooBee

input: "Question,2b.or !tooBee." output:

Chapter 9 5

Testing for "End of File" in a Text File

text files end with a special character: EOF during the reading of a text file, Java can detect if the EOF

character has been readEOF = ASCII value 26 (end of file)CR = ASCII value 13 (carriage return) – '\r'NL = ASCII value 10 (linefeed, newline) – '\n'Tab = ASCII value 9 – '\t'

if .readLine() attempts to read beyond the EOF char, it returns a null value (test for this to stop)

if .read() returns an Integer value -1; the Unicode value -1, is special since all characters are positive

IMPORTANT: » neither of these methods throws an EOFException. how is

this possible ?

Chapter 9 6

int count = 0; String line = inputStream.readLine(); while (line != null) { count++; outputStream.println(count + " " + line); line = inputStream.readLine(); }

Chapter 9 Java: an Introduction to Computer Science & Programming - Walter Savitch 6

Excerpt from TextEOFDemo

Example: Using Null toTest for End-of-File in a Text File

When using readLine()test for null

When using read() test for -1

Chapter 9 7

Examining class SavitchIn: readChar() Method

public static char readChar(){

int charAsInt = -1;try{

charAsInt = System.in.read();}catch (IOException e){

System.out.println(e.getMessage());System.out.println("IO error. End.");System.exit(0);

}

return (char)charAsInt;}// end of readChar()

Returns an int, not a char

Initialized to avoid compiler error message.

Chapter 9 8

Examining Class SavitchIn:readLine() Method

public static String readLine(){

char nextChar;String result = "";boolean done = false;while (!done){

nextChar = readChar();if (nextChar == '\n') done = true;else if (nextChar == '\r'){ }else result = result + nextChar;

}return result;

}// end of readLine()

Do nothing. Next iteration will detect '\n'

'\r' is carriage return symbol.some systems use "\r\n" to indicate "end of a line."

Add any char except '\r' and '\n' to result string.

Chapter 9 9

In place of a String filename: the File class

acts like a wrapper class for file names

file name, "numbers.dat" is only a String

a file name of type File, has special methods» .exists(): return boolean, if file already exists» .canRead(): return boolean, if file can be read» see page 570-573

FileInputStream, FileReader,and FileOutputStream have constructors that take a File argument» similar to the constructors that take String arguments