File Handling in Java

File handling lets a program read data from files and write data that can be used later. A path identifies a file or directory. Opening, reading, and writing can fail, so programs also need to handle errors and close resources.

Why Do We Need This?

A practice app may keep notes in a text file. It needs to choose where the file is located, how text is encoded, and whether writing should replace or append to existing contents.

Main Ideas

Simple Working Example

Run this program on its own. All required imports and classes are included.

import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Collections;
 
public class HelloWorld {
    public static void main(String[] args) throws Exception {
        Path notes = Files.createTempFile("java-notes-", ".txt");
        try {
            Files.write(notes, Collections.singletonList("Practice one example"),
                    StandardCharsets.UTF_8);
            for (String line : Files.readAllLines(notes, StandardCharsets.UTF_8)) {
                System.out.println(line);
            }
        } finally {
            Files.deleteIfExists(notes);
        }
    }
}

Output

Practice one example

The program creates its own temporary input file, writes one line, reads it, and removes it. readAllLines is convenient for this tiny example; use gradual reading for large files.

Topics in This Section

• Java File Handling
• Serialization & Deserialization

Easy Way to Remember

Choose the path, encoding, and resource lifetime deliberately. A file example should state which input files it needs and which files it creates.