# Reading & Writing Files — Core Java

Source: https://www.geekswithgeeks.com/en/core-java/java-file-io

> Read and write files with the modern java.nio.file API, fall back to Scanner for quick line-by-line reads, and always close resources with try-with-resources.

## java.io vs java.nio.file

The classic `java.io` package (`FileReader`, `BufferedReader`) still works everywhere. Since Java 7, `java.nio.file` — `Path` and `Files` — offers a friendlier, more modern API for most everyday file tasks and is the recommended starting point.

## Reading with Files

`Files.readString` and `Files.readAllLines` are one-liners for small-to-medium files. For huge files, stream lines instead of loading everything into memory.

```java
Path path = Path.of("notes.txt");
String whole = Files.readString(path);
List<String> lines = Files.readAllLines(path);

try (var stream = Files.lines(path)) {
    stream.filter(l -> !l.isBlank()).forEach(System.out::println);
}
```

## Writing & Scanner for files

`Files.writeString` writes (or creates) a file in one call. `Scanner` can also wrap a `File` directly — handy for reading structured, token-by-token input the same way you read from the console.

```java
Files.writeString(Path.of("out.txt"), "hello\n", StandardOpenOption.CREATE, StandardOpenOption.APPEND);

try (Scanner sc = new Scanner(new File("scores.txt"))) {
    while (sc.hasNextInt()) {
        System.out.println(sc.nextInt());
    }
} catch (FileNotFoundException e) {
    throw new UncheckedIOException(e);
}
```

## Always close, always handle IOException

File handles are a limited OS resource — always open them in a `try-with-resources`. Almost every file operation throws the **checked** `IOException`, so the compiler will remind you if you forget.