File Navigation and I/O. Practical Tasks

Write the euro sign to a file through FileOutputStream and read it back: instead of € you get ¬, and no exception is thrown anywhere:

try (OutputStream out = new FileOutputStream("a.txt")) {
    out.write('€');                        // write(int) keeps only the low byte: 0x20AC -> 0xAC
}
try (InputStream in = new FileInputStream("a.txt")) {
    System.out.println((char) in.read());  // Output: ¬
}

These Java I/O streams exercises practice the module «Java I/O»: you will rewrite byte-by-byte file copying with try-with-resources, copy a text file line by line with BufferedReader and BufferedWriter, walk a directory tree recursively with the File class, and write reports to a file with PrintWriter in two course projects — the Employee Report and the Online Store. All six tasks have hints, and the section after the tasks lists the mistakes that leave a file empty, truncated or garbled without a single exception.

What to Review Before You Start

The six tasks need three skills: reading and writing byte and character streams, closing them automatically with try-with-resources, and listing a directory with the File class. If any of them feels shaky, open the lesson section from the table first — each rule is explained there with a runnable example.

FileCopy: Rewrite with try-with-resources

Rewrite the class FileCopy, which copies a file byte by byte:

package io;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileCopy {
    public static void main(String[] args) throws IOException {
        FileInputStream fileIn = null;
        FileOutputStream fileOut = null;

        try {
            fileIn = new FileInputStream("src/io/file.txt");
            fileOut = new FileOutputStream("src/io/copied_file.txt");

            int a;
            while ((a = fileIn.read()) != -1) {
                fileOut.write(a);
            }
        } finally {
            if (fileIn != null) {
                fileIn.close();
            }
            if (fileOut != null) {
                fileOut.close();
            }
        }
    }
}

1. Replace the manual closing of the streams in the finally block with try-with-resources.
2. Add a catch block that handles IOException and remove throws IOException from the signature of main.

FileInputOutputStreamDemo: Write and Read Bytes

Rewrite the class FileInputOutputStreamDemo:

package io;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.IOException;

public class FileInputOutputStreamDemo {
    public static void main(String[] args) {
        try {
            char[] symbols = {'a', 'b', 'c'};
            OutputStream output = new FileOutputStream("a.txt");
            for (int i = 0; i < symbols.length; i++) {
                // write each character to the text file
                output.write(symbols[i]);
            }
            output.close();

            InputStream input = new FileInputStream("a.txt");
            int size = input.available();

            for (int i = 0; i < size; i++) {
                // read the text file character by character
                System.out.print((char) input.read() + " ");
            }
            input.close();
        } catch (IOException e) {
            System.out.print("Exception");
        }
    }
}

1. Rewrite the code with try-with-resources for OutputStream and InputStream.
2. Replace the writing loop for (int i = 0; i < symbols.length; i++) with a for-each loop.
3. Write the file a.txt to the src/io directory: the file path is "src/io/a.txt".

Expected output: a b c

Copy a Text File Line by Line

1. Write a class that copies the contents of one text file to another, line by line.
2. Read with BufferedReader on top of FileReader, and write with BufferedWriter on top of FileWriter.
3. Close the streams with try-with-resources.

Write the Employee Report to a File

Employee Report · part 4 of 4 · ← part 2

1. Add a method to the Employee class that writes the employee report to a file.
2. Use the PrintWriter class.

Recursive Directory Listing with the File Class

1. Write a method that recursively walks a given directory and prints information about all files and directories in it and in all of its subdirectories.
2. Use the File class and recursion.

Save the Purchase Receipt to a File

Online Store · part 8 of 8 · ← part 7

Earlier parts of the project: part 1, part 2, part 3, part 4, part 5, part 6, part 7.

1. After the purchase is completed, write a report on the contents of the shopping cart to a file.
2. Use the PrintWriter class to write and format the report.

Where I/O Solutions Fail Silently

Most broken I/O solutions fail without an exception: the program finishes, but the file is empty, truncated or full of wrong characters. The cause is almost always the wrong kind of stream, a buffer that was never flushed, or the default charset. The table lists the typical slips and how to fix each one.