Summary - File I/O

Combine BufferedReader and PrintWriter to write a notes app.

Summary - File operations

In this group you learned file operations. File represents a path; FileWriter and FileReader read and write characters. With BufferedReader you read line by line, with PrintWriter you write formatted output. try-with-resources closed resources automatically.

This summary combines everything in a small task: write lines to a file and then read them back.

Exercise Write and read back

First, in a try (PrintWriter pw = new PrintWriter("summary.txt", "UTF-8")) block, write pw.println("One"); and pw.println("Two");. Then, in a try (BufferedReader r = new BufferedReader(new FileReader("summary.txt"))) block, call System.out.println(r.readLine()); twice.

Show example solution

import java.io.PrintWriter;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class Main {
    public static void main(String[] args) throws IOException {
        try (PrintWriter pw = new PrintWriter("summary.txt", "UTF-8")) {
            pw.println("One");
            pw.println("Two");
        }
        try (BufferedReader r = new BufferedReader(new FileReader("summary.txt"))) {
            System.out.println(r.readLine());
            System.out.println(r.readLine());
        }
    }
}

Test yourself

Which structure auto-closes resources?
- try-with-resources
- try { } catch
- finally { }
- static import
Show answer

try-with-resources — try-with-resources calls close automatically at the end.

Complete the line-reading method

String line = r.____();

Show answer

String line = r.readLine();

Match the file operations summary

File

Represents a path
BufferedReader

Reads line by line
PrintWriter

Writes formatted output
try-with-resources

Auto-closes resources

Next lesson: Jackson ObjectMapper

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