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Java Dictionary

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Files.readString() / Files.readAllLines()

Files.readString() / Files.readAllLines()

Methods for reading a file's contents as a string or a list of lines in a single call (Java 11+). Using the utility methods of the Files class lets you read files with less code than traditional BufferedReader approaches.

Syntax

// Reads the entire file as a string (Java 11+).
String content = Files.readString(Path.of("file-path"));

// Reads all lines of the file as a list.
List<String> lines = Files.readAllLines(Path.of("file-path"));

// Reads all lines of the file as a stream (Java 8+).
Stream<String> lineStream = Files.lines(Path.of("file-path"));

// Creates a path object (Java 11+).
Path path = Path.of("file-path");

Method List

Method	Description
Files.readString(Path)	Reads the entire file as a UTF-8 string (Java 11+). You can also specify a character encoding as the second argument.
Files.readAllLines(Path)	Reads all lines of the file as a `List<String>`. Line endings are not included.
Files.lines(Path)	Returns all lines of the file as a `Stream<String>` (Java 8+). Useful for lazily reading large files.
Path.of(String)	Creates a path object from a string (Java 11+). Equivalent to `Paths.get()`.

Sample Code

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.List;

// Reads the entire file as a string (Java 11+).
try {
    String content = Files.readString(Path.of("sample.txt"));
    System.out.println(content); // Prints the file contents.
} catch (IOException e) {
    e.printStackTrace();
}

// Reads all lines of the file as a list.
try {
    List<String> lines = Files.readAllLines(Path.of("sample.txt"));
    System.out.println("Line count: " + lines.size());
    for (String line : lines) {
        System.out.println(line);
    }
} catch (IOException e) {
    e.printStackTrace();
}

// Processes lines using a stream (useful for large files).
try (var stream = Files.lines(Path.of("sample.txt"))) {
    stream
        .filter(line -> line.startsWith("//"))
        .forEach(System.out::println); // Prints only comment lines.
} catch (IOException e) {
    e.printStackTrace();
}

Notes

Both readString() and readAllLines() load the entire file into memory, so reading very large files (several hundred MB or more) may cause an out-of-memory error. For large files, use Files.lines() or BufferedReader to process the file one line at a time.

Because Files.lines() returns a Stream, use it inside a try-with-resources block. If you do not close the stream, the file handle will not be released. The default encoding is UTF-8; if your file uses a different encoding, pass a Charset as the second argument (e.g., Charset.forName("Shift_JIS")).

For writing to files, see Files.writeString() / Files.write().

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