new BufferedReader() / reader.readLine()

// Create a BufferedReader to read from standard input.
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

// Create a BufferedReader to read from a file.
BufferedReader reader = new BufferedReader(new FileReader("file path"));

// Read one line (returns null at the end of the file).
String line = reader.readLine();

BufferedReaderExample.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;

class BufferedReaderExample {
    public static void main(String[] args) {
        // Read one line from standard input.
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            System.out.print("Enter input: ");
            String line = reader.readLine();
            System.out.println("You entered: " + line);
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Read a file line by line.
        try (BufferedReader br = new BufferedReader(new FileReader("sample.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line); // Each line is printed.
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Process lines as a stream using lines() (Java 8+).
        try (BufferedReader br = new BufferedReader(new FileReader("sample.txt"))) {
            br.lines()
              .filter(l -> !l.isEmpty())
              .forEach(System.out::println); // Each non-empty line is printed.
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

The command looks like this:

javac BufferedReaderExample.java
java BufferedReaderExample
Enter input: Hello
You entered: Hello
Yagami Light
L Lawliet
Amane Misa
Yagami Light
Amane Misa

Common Mistake 1: Forgetting close() causes a resource leak

If you don't call close() on a BufferedReader after you're done with it, the file handle is not released and a resource leak occurs. It's like Yagami Light leaving evidence lying around instead of disposing of it.

ReaderLeakNg.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

class ReaderLeakNg {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new FileReader("sample.txt"));
        String line = br.readLine();
        System.out.println(line);
    }
}

The command looks like this:

javac ReaderLeakNg.java
java ReaderLeakNg
Yagami Light

Use the try-with-resources syntax to call close() automatically when the block exits. Just as L Lawliet carefully handles evidence, always close your resources reliably.

ReaderLeakOk.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

class ReaderLeakOk {
    public static void main(String[] args) throws IOException {
        try (BufferedReader br = new BufferedReader(new FileReader("sample.txt"))) {
            String line = br.readLine();
            System.out.println(line);
        }
    }
}

The command looks like this:

javac ReaderLeakOk.java
java ReaderLeakOk
Yagami Light

Common Mistake 2: Not checking for null from readLine() causes NullPointerException

readLine() returns null when it reaches the end of the file. If you forget the null check, calling a method on the returned value throws a NullPointerException. Check for null before proceeding, like Amane Misa double-checking her Shinigami Eyes deal.

ReadLineNullNg.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

class ReadLineNullNg {
    public static void main(String[] args) throws IOException {
        try (BufferedReader br = new BufferedReader(new FileReader("sample.txt"))) {
            String line = br.readLine();
            System.out.println(line.toUpperCase());
        }
    }
}

The command looks like this:

javac ReadLineNullNg.java
java ReadLineNullNg
Exception in thread "main" java.lang.NullPointerException

Always include a null check in the while condition when reading lines, as Near would cautiously verify every step before concluding.

ReadLineNullOk.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

class ReadLineNullOk {
    public static void main(String[] args) throws IOException {
        try (BufferedReader br = new BufferedReader(new FileReader("sample.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line.toUpperCase());
            }
        }
    }
}

The command looks like this:

javac ReadLineNullOk.java
java ReadLineNullOk
YAGAMI LIGHT
L LAWLIET
AMANE MISA

Because BufferedReader uses an internal buffer, it is significantly faster than using FileReader alone, which reads one character at a time. readLine() returns null at the end of the file, so be sure to include a null check in your while condition.

Using the try-with-resources syntax from Java 7 onward (try (BufferedReader br = ...)) automatically calls close() when the block exits. Use this syntax to avoid accidentally forgetting to close the stream.

For reading an entire file at once, see Files.readString() / Files.readAllLines().