CS101 Lab

“File input/Output”

File input, output

• File : binary file, text file

• READ/WRITE class of “text file”

- File Reading class

: FileReader, BufferedReader

- File Writing class

: FileWriter, FileOutputStream, PrintWriter

- import java.io.*;

Reading from Text file

FileReader fr = new FileReader( “input.txt” ); BufferedReader inputStream = new BufferedReader( fr );

BufferedReader inputStream = new BufferedReader( new FileReader(“input.txt”) );

File access obejct

File reading object

* Usage : inputStream.read(); inputStream.readLine();

readLine() method

Read a line of the text file Return null if the end of the stream has been

reached

BufferedReader inputStream =

new BufferedReader( new FileReader(“input.txt”) );

String s;

While((s = inputStream.readLine()) != null) {

do something with s;

}

Exception Handling in File IO

- FileNotFoundException : if the named file does not exist- IOException : if an I/O error occurs

- public String readLine() throws IOException

- public FileReader(String fileName) throws FileNotFoundException

try{

BufferedReader reader = new BufferedReader(new FileReader(“input.txt”));

String line = reader.readLine();

…

} catch (FileNotFoundException e) {

…

} catch (IOException e) {

…

}

QUIZ

Print all contents in “input.txt” BufferedReader inputStream = new

BufferedReader( new FileReader(“input.txt”) );

String s;

While((s = inputStream.readLine()) != null) {

System.out.println(s);

}

Write text to file

FileOutputStream fw = new FileOutputStream( “out.txt” );PrintWriter outputStream = new PrintWriter( fw, true );

PrintWriter outputStream = new PrintWriter( new FileOutputStream(“out.txt”), true );

PrintWriter outputStream = new PrintWriter( new FileWriter(“out.txt”), true );

File access object

File reading object

* Usage : outputStream.print( … ); outputStream.println( … );

StringTokenizer

- Break a string into tokens by delimiters (the characters that separate tokens)

ex) “I_am_a_students.”

~> delimiter : “_” 4 tokens

delimiter : “ ” 1 tokens

public StringTokenizer(String str, String delim)

import java.util.*; StringTokenizer tokenizer = new StringTokenizer(str, “\t”); String token = tokenizer.nextToken(); // return next tokens int count = tokenizer.countTokens(); // return the number of left tokens

BufferedReader input = new BufferedReader( new FileReader("in.txt") );

String str;While((str = input.readLine()) != null) {

StringTokenizer token = new StringTokenizer(str, “ ”);int ID = Integer.parseInt(token.nextToken());String name = token.nextToken();String depart = token.nextToken();

}

StringTokenizer

20050001 Hong No

20040002 Kim CS

20030001 Na PH

in.txt

import java.io.*;import java.util.*;

public class FileReadWriteTest {

public static void main(String[] args) { try { BufferedReader in = new BufferedReader( new FileReader("in.txt") ); PrintWriter out = new PrintWriter( new FileOutputStream("out.txt") , true); String s; while ((s = in.readLine()) != null) { StringTokenizer token = new StringTokenizer(s," "); String name = token.nextToken(); int borrowing = Integer.parseInt(token.nextToken()); System.out.println(name + " " + borrowing); out.println(name + " " + borrowing); } } catch (FileNotFoundException e) { System.out.println(e.getMessage()); } catch (IOException e) { System.out.println(e.getMessage()); } System.exit(0); }}

Kim 30000

Choi 20000

Oh 10000

in.txt

Practice

Implement a progrm that executes correctly the following procedures Read the “data.txt” file Get the information of employee from “data.txt” file Make linked list using the information Save the information of employees into the

“output_A(Class name).txt” file RequirementsRequirements

1. Download “EmployeeNode.java”, “EmployeeList.java” from cs101 homepage and use them

2. Add two method in EmployeeList classa. public EmployeeNode getHead() : return head nodeb. public int getNodeLength() : return the number of nodes

3. Implement ListTest_A(class name).javaa. Implement two method

- public static void GetData(String filename, EmployeeList list) method : Read Data from file, and save the data into the linked list- public static void SaveData(String filename, EmployeeList list) method : Save Data in the linked list into file

b. Add Exception Handling in GetData, SaveData method: using try { } catch (Exception) { }

c. main method • Download “data.txt” from the cs101 homepage.

• In each line, one employee’s data is saved in the file.• Each data separate by tab(“\t”).

• The name of output file is “output_A(class name).txt”.• You can determine path of the directory.

public class ListTest_A { ……

public static void main(String[] args) { EmployeeList list = new EmployeeList(); GetData("c:/data.txt", list); // you may modify the path of the text file String output = "Linked list size : " + list.getNodeLength() + "\n" + list; list.DeleteNode("003"); list.InsertNode(“Kang,Dong-il", 2004, "010"); list.DeleteNode("005"); output += "\nLinked list size : " + list.getNodeLength() + "\n" + list; JTextArea area = new JTextArea(); area.setText(output); JOptionPane.showMessageDialog(null,area); SaveData("c:/output_class name.txt", list);

// you may modify the path of the text file

System.exit(0);}

}

Result