Reading files

Read an entire file into a String with one line.

I/O

Code Comparison

✕ Java 8

StringBuilder sb = new StringBuilder();
try (BufferedReader br =
    new BufferedReader(
        new FileReader("data.txt"))) {
    String line;
    while ((line = br.readLine()) != null)
        sb.append(line).append("\n");
}
String content = sb.toString();

✓ Java 11+

String content =
    Files.readString(Path.of("data.txt"));

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Why the modern way wins

📏

One line

Replace 8 lines of BufferedReader boilerplate.

🧹

Auto cleanup

File handle is closed automatically.

🌐

UTF-8 default

Correct encoding by default — no charset confusion.

Old Approach

BufferedReader

Modern Approach

Files.readString()

Since JDK

Difficulty

Beginner

JDK Support

Reading files

Available

Widely available since JDK 11 (Sept 2018)

How it works

Files.readString() reads a file's entire content into a String. It handles encoding (UTF-8 by default) and resource cleanup. For large files, use Files.lines() for lazy streaming.

Try-with-resources improvement

Java 8

Connection conn = getConnection();
// Must re-declare in try
try (Connection c = conn) {
    use(c);
}

Java 9+

Connection conn = getConnection();
// Use existing variable directly
try (conn) {
    use(conn);
}

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JDK 9+ →

I/O Beginner

Writing files

Java 8

try (FileWriter fw =
        new FileWriter("out.txt");
    BufferedWriter bw =
        new BufferedWriter(fw)) {
    bw.write(content);
}

Java 11+

Files.writeString(
    Path.of("out.txt"),
    content
);

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JDK 11+ →

I/O Beginner

Files.mismatch()

Java 8

// Compare two files byte by byte
byte[] f1 = Files.readAllBytes(path1);
byte[] f2 = Files.readAllBytes(path2);
boolean equal = Arrays.equals(f1, f2);
// loads both files entirely into memory

Java 12+

long pos = Files.mismatch(path1, path2);
// -1 if identical
// otherwise: position of first difference

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JDK 12+ →