FILE, INPUT, AND OUTPUT

💾 FILE, INPUT, AND OUTPUT

(IT2408 – 04 Handout 1 Study Guide)

🗂 1. Computer Files

📌 What is a Computer File?

A computer file is a collection of data stored on a permanent storage device like:

• Hard disk

• USB

• CD

• Magnetic tape

Files have:

• 📏 Size

• 🏷 Name

• 🕒 Creation date

In short:

📂 Types of Files

According to page 1, files are categorized by how they store data:

📝 Text Files

• Encoded in ASCII or Unicode

• Can be opened in a text editor

• Examples:

  • Payroll data

  • Program files

  • Application files

You can actually read these.

💻 Binary Files

• Stored in 0s and 1s

• Not readable in a text editor

• Examples:

  • Images

  • Music

  • Compiled .class files

You see weird symbols if you open it in Notepad 😭

📁 Directory Structure & Paths

🏠 Root Directory

Main folder of storage device.

Example:
C:\

📂 Folder Hierarchy

Folders inside folders = hierarchy.

Example from page 1:

C:\Java\Chapter.11\Data.txt

🛣 What is a Path?

A path is the complete location of a file in a directory structure.

Windows

Uses backslash:

\

UNIX/Solaris

Uses forward slash:

/

📌 2. Common File Tasks (Very Exam Important)

From page 2:

Applications usually:

• Check if file exists

• Open file

• Write to file

• Read from file

• Close file

• Delete file

Think of it like file life cycle.

🧠 3. Path and Files Classes (Java NIO)

To use:

import java.nio.file.*;

nio = new input/output

🔹 Path Class

Used to:

• Store file information

• Location

• Size

• Creation date

• Check existence

Path creates the reference.

🔹 Files Class

Used to:

• Delete files

• Check attributes

• Create streams

Files performs the action.

Mnemonic:

🏗 Creating a Path

Method 1: Using FileSystem

FileSystem fs = FileSystems.getDefault();
Path filePath = fs.getPath("C:\\Java\\Chapter.11\\Data.txt");

⚠ Important:

In Java, \ is an escape character.

So you must write:

\\

Method 2: Using Paths Class (Simpler)

Path filePath = Paths.get("C:\\Java\\Chapter.11\\SampleFile.txt");

This is easier and more common.

📍 Absolute vs Relative Path

From page 3:

🔵 Absolute Path

Complete path from root.

Example:

C:\Java\Chapter.11\SampleFile.txt

Needs no extra info.

🟢 Relative Path

Depends on current directory.

Example:

SampleFile.txt

Assumes file is in same folder as program.

🔄 Converting Relative to Absolute

Method:

toAbsolutePath()

Example from PathDemo2 program:

User enters filename

• Program converts it to full path

If already absolute → no change
If relative → converts to absolute

🔍 Retrieving Path Information

From page 3–4 table:

Important:

• Index starts at 0

• Last index = getNameCount() - 1

🔐 Checking File Accessibility

Method:

checkAccess()

Import:

import static java.nio.file.AccessMode.*;

Options:

• No argument → check existence

• READ → check read permission

• WRITE → check write permission

• EXECUTE → check execute permission

Alternative:

Files.exists(path)

⚠ Throws IOException if inaccessible.

From PathDemo3 example:

Checks READ and EXECUTE

• Uses try-catch

📊 Determining File Attributes

Method:

Files.readAttributes()

Returns:

BasicFileAttributes

Example:

BasicFileAttributes attr =
Files.readAttributes(filePath, BasicFileAttributes.class);

Then you can call:

• size()

• creationTime()

• lastModifiedTime()

FileTime format:

yyyy-mm-ddThh:mm:ss

From page 6

🔄 IO Classes Hierarchy

From diagram on page 6:

Object
→ InputStream
→ OutputStream
→ Reader

Important subclasses:

Input Side

• FileInputStream

• BufferedInputStream

Output Side

• FileOutputStream

• BufferedOutputStream

• PrintStream (System.out)

Character Streams

• Reader

• BufferedReader

• BufferedWriter

📤 OutputStream Methods (Exam Alert 🚨)

From page 7 table:

💻 ScreenOut Program Explained

From page 7–8:

String s = "ABCDF";
byte[] data = s.getBytes();
OutputStream output = System.out;
output.write(data);
output.flush();
output.close();

What happens?

1. String converted to byte array

2. OutputStream points to System.out

3. write() sends bytes to screen

4. flush() forces output

5. close() releases stream

Result:

ABCDF

🎯 QUICK SUMMARY SECTION

🧠 File Types

Text = readable

Binary = unreadable

🧠 Path Types

Absolute = full address

Relative = depends on location

🧠 Path vs Files

Path = describes file

Files = performs operation

🧠 Key Methods to Memorize

Path:

• toString()

• getFileName()

• getNameCount()

• getName()

Files:

• exists()

• readAttributes()

OutputStream:

• write()

• flush()

• close()

🧩 MEMORY TRICKS

📁 File Tasks = OWRRCD

Open

Write

Read

Remove

Check

Delete

📍 Path Types

A = Absolute = All info

R = Relative = Relies on location

🔄 OutputStream Flow

Write → Flush → Close

Mnemonic: