Module 4: File I/O

Learning Objectives

• Know how to write to a file
• Know how to read from a file
• Understand opening and closing file streams
• Understand using a buffer array to hold chunks from a file
• Catch/throw file related exceptions

File I/O in Java Explained

File Input/Output (I/O) operations are essential for working with external data sources in Java applications. These operations allow you to read data from files and write data to files.

Basic File I/O Operations

• Locating files: Using the File class to represent file paths
• Reading files: Loading content from a file into your program
• Writing files: Saving content from your program to a file
• Closing resources: Properly releasing system resources when finished

Reading Text Files

Java provides several ways to read text files. One common approach uses FileReader and BufferedReader:

FileReader fileReader = new FileReader(file);
BufferedReader bufferedReader = new BufferedReader(fileReader);
String fileContents = "";

String line = bufferedReader.readLine();  
while (line != null) {
    fileContents += line + "\n";
    line = bufferedReader.readLine();
}

bufferedReader.close();

Writing Text Files

For writing to text files, you can use FileWriter and BufferedWriter:

FileWriter fileWriter = new FileWriter(file);
BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);

bufferedWriter.write("Hello World!");

bufferedWriter.close();

Working with Binary Files

For binary files or when you need to work with any file type, use FileInputStream and FileOutputStream:

FileInputStream inStream = new FileInputStream(inFile);
byte[] buffer = new byte[256];
int bytesRead = inStream.read(buffer);

while (bytesRead > 0) {
    // Process bytes
    bytesRead = inStream.read(buffer);
}

inStream.close();

Exception Handling

File operations require proper exception handling:

• FileNotFoundException: When the specified file cannot be found
• IOException: For general I/O errors during file operations
• Always use try-catch blocks or proper exception propagation

Key Topics

Resources

Practice Exercises

Next Steps