How to write text to a file

Short answer

Files.writeString() creates a file or overwrites an existing one:

void main() throws IOException {
    Path file = Path.of("hello.txt");
    Files.writeString(file, "Hello, file!\n");
 
    IO.print(Files.readString(file));
}

Output:

Hello, file!

A list of lines

Files.write() writes each line of a list followed by a line break:

void main() throws IOException {
    var lines = List.of("apples", "pears", "plums");
    Files.write(Path.of("fruits.txt"), lines);
 
    IO.println(Files.readAllLines(Path.of("fruits.txt")));
}

Output:

[apples, pears, plums]

Many writes

For writing in a loop use a BufferedWriter — it collects data and writes it to disk in large chunks:

void main() throws IOException {
    Path file = Path.of("squares.txt");
    try (BufferedWriter writer = Files.newBufferedWriter(file)) {
        for (int i = 1; i <= 3; i++) {
            writer.write(i + " * " + i + " = " + i * i);
            writer.newLine();
        }
    }
    IO.print(Files.readString(file));
}

Output:

1 * 1 = 1
2 * 2 = 4
3 * 3 = 9

Common mistake

Writing into a folder that does not exist. Java does not create folders for you:

void main() throws IOException {
    Files.writeString(Path.of("reports/2026/march.txt"), "data");
}

Output:

Exception in thread "main" java.nio.file.NoSuchFileException: reports\2026\march.txt

Create the folders first: Files.createDirectories(file.getParent()).

Thanks for reading!

Short answer

A list of lines

Many writes

Common mistake

Functions used in this recipe

Thanks for reading!