Download BufferedReader inputStream = new BufferedReader

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
File access obejct
FileReader fr = new FileReader( “input.txt” );
BufferedReader inputStream = new BufferedReader( fr );
File reading object
BufferedReader inputStream =
new BufferedReader( new FileReader(“input.txt”) );
* Usage : inputStream.read(); inputStream.readLine();
readLine() method
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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
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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
File access object
FileOutputStream fw = new FileOutputStream( “out.txt” );
PrintWriter outputStream = new PrintWriter( fw, true );
File reading object
PrintWriter outputStream =
new PrintWriter( new FileOutputStream(“out.txt”), true );
PrintWriter outputStream =
new PrintWriter( new FileWriter(“out.txt”), true );
* 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
StringTokenizer
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();
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) {
Kim 30000
System.out.println(e.getMessage());
Choi 20000
} catch (IOException e) {
System.out.println(e.getMessage());
Oh 10000
}
in.txt
System.exit(0);
}
}
Practice
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Implement a progrm that executes correctly the following
procedures
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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
Requirements
1. Download “EmployeeNode.java”, “EmployeeList.java” from
cs101 homepage and use them
2. Add two method in EmployeeList class
a. public EmployeeNode getHead() : return head node
b. public int getNodeLength() : return the number of nodes
3. Implement ListTest_A(class name).java
a. 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);
}
}
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Result