Java Files (File I/O)IST 256

Application Programming for Information SystemsXiaozhong Liu

Yatish Hegde

https://xliu12.mysite.syr.edu/

File I/O

Hard Disk(Secondary Memory)

Memory(Primary Memory)

Read

Write

Process

I/O Streams

Input Stream

Output Stream

Default input/output streams

Java - Streams

JAVA provides 2 types of streams

Text streams - containing ‘characters‘

I ‘ M A S T R I N G \nProgram Device

Binary Streams - containing 8 – bit information

01101001Program Device11101101 00000000

Reading and Writing Files

Create a stream object and associate it with a disk-file

Give the stream object the desired functionality

while there is more information read(write) next data from(to) the stream

close the stream

public static void readFile(){

BufferedReader ins = new BufferedReader(new FileReader(“test.txt”));while(ins.ready()){

String s = ins.readLine();System.out.println(s);

}ins.close();

}

Reading Files

Important: Place the code insideTry{…}Catch{….}Wherever necessary

import java.io.*;

public static void writeFile(){

String s = “I love programming”;BufferedWriter outs = new BufferedWriter(new FileWriter(“test_out.txt”));outs.write(s);

}outs.close();

Writing File

Important: Place the code insideTry{…}Catch{….}Wherever necessary

import java.io.*;

Public static void readFile(){

BufferedReader ins = new BufferedReader(new FileReader(“test.txt”));Scanner scanner = new Scanner(ins);while(scanner.hasNext()){

System.out.println(scanner.next());}scanner.close();

}

Reading tokens from file

Important: Place the code insideTry{…}Catch{….}Wherever necessary

import java.io.*;Import java.util.Scanner;

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt)

{JFileChooser fc = new JFileChooser();

if(fc.showOpenDialog(this) == JFileChooser.APPROVE_OPTION) { File file = fc.getSelectedFile(); String inputFilePath = file.getAbsolutePath().toString(); jTextField1.setText(inputFilePath); } }

Browse Files using GUI

Try this for fun In a notepad, type few sentences and save the

file as test.txt. Write a Java program to read the text in test.txt and write that to file test_out.txt.

In a notepad, type 10 numbers (any numbers in the range 0 to 10) separated by white space and save the file as grade.txt. Write a Java program to read the numbers from grade.txt, calculate the average grade and print the output.

In a notepad, type five names (one name per line) and save the file as name.txt. Create a GUI from which you can select (browse button) the file name.txt and write (create button) the names in name.txt to file name_out.txt (one name per line).