📖 Java Read Files – Efficient File Reading in Java

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🧲 Introduction – Why File Reading Matters

Reading data from files is a critical part of many Java applications—whether it’s loading configuration settings, importing datasets, or reading logs. Java provides a variety of APIs to read files, from traditional methods like FileReader to modern approaches like Files.readAllLines().

✅ In this guide, you’ll learn:

• How to read files in Java using different techniques
• When to use FileReader, BufferedReader, Scanner, or Files
• How to handle exceptions and resources safely
• Performance tips and best practices for large file reading

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📦 Java File Reading Classes

Class/Method	Use Case
FileReader	Basic character stream reading
BufferedReader	Efficient reading of text, line by line
Scanner	Token-based reading (great for parsing)
Files.readAllLines()	Simple and modern, reads all lines into a list
Files.lines()	Lazy stream-based reading

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📄 Read File Using FileReader

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

public class FileReaderExample {
    public static void main(String[] args) {
        try (FileReader reader = new FileReader("example.txt")) {
            int character;
            while ((character = reader.read()) != -1) {
                System.out.print((char) character);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

✅ Explanation:

• Reads character-by-character
• Suitable for small text files
• Uses try-with-resources to auto-close

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📘 Read File Using BufferedReader

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

public class BufferedReaderExample {
    public static void main(String[] args) {
        try (BufferedReader br = new BufferedReader(new FileReader("example.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

✅ Explanation:

• Efficient for line-by-line reading
• Avoids character-by-character I/O bottlenecks
• Ideal for reading logs or text files line-by-line

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🔍 Read File Using Scanner

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class ScannerExample {
    public static void main(String[] args) {
        try (Scanner scanner = new Scanner(new File("example.txt"))) {
            while (scanner.hasNextLine()) {
                System.out.println(scanner.nextLine());
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}

✅ Explanation:

• Great for parsing numbers, words, tokens
• Use .hasNext(), .nextInt(), .nextDouble() etc.
• More flexible for structured file content

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🚀 Read All Lines Using Files.readAllLines()

import java.nio.file.*;
import java.io.IOException;
import java.util.List;

public class FilesReadAllLinesExample {
    public static void main(String[] args) throws IOException {
        List<String> lines = Files.readAllLines(Paths.get("example.txt"));
        lines.forEach(System.out::println);
    }
}

✅ Explanation:

• Reads all lines into a List<String>
• Simple and modern, but loads entire file into memory
• Suitable for small to medium files

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🌊 Stream-based Reading Using Files.lines()

Files.lines(Paths.get("example.txt"))
     .filter(line -> !line.isEmpty())
     .forEach(System.out::println);

✅ Explanation:

• Returns a Stream of lines for efficient, lazy processing
• Can filter, map, reduce during reading

💡 Tip: Always close streams or use try-with-resources.

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📊 Comparison Table

Method	Best For	Memory Usage	Buffered?	Java Version
FileReader	Small files, character reading	Low	❌	1.0+
BufferedReader	Line-by-line reading	Low	✅	1.1+
Scanner	Token parsing	Medium	✅	1.5+
Files.readAllLines()	Small to mid files	High	✅	1.7+
Files.lines()	Large files, streaming processing	Low (streamed)	✅	1.8+

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💡 Best Practices

• ✅ Use BufferedReader or Files.lines() for large files
• ✅ Always use try-with-resources to auto-close readers
• ⚠️ Avoid readAllLines() on large files — memory overload
• ✅ Prefer Files API for modern Java apps
• 🔒 Handle IOException and FileNotFoundException properly

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📌 Summary – Java File Reading Techniques

Java offers flexible file reading methods for different scenarios — whether you need line-by-line efficiency, token-based parsing, or modern stream processing.

🧾 Key Takeaways:

• Use FileReader and BufferedReader for traditional reading
• Use Scanner for parsing structured text
• Use Files.readAllLines() for simplicity (small files)
• Use Files.lines() for memory-efficient streaming
• Apply try-with-resources and exception handling always

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❓FAQs – Java Read Files

❓ What is the easiest way to read a file in Java?

Use Files.readAllLines() for small files or Files.lines() for large files with stream processing.

❓ How to read a file line-by-line in Java?

Use BufferedReader.readLine() inside a loop or Scanner.nextLine().

❓ Which is better: BufferedReader or Scanner?

Use BufferedReader for performance, and Scanner for parsing tokens like integers or words.

❓ How to avoid memory issues with large files?

Use Files.lines() or BufferedReader, which read line-by-line instead of loading entire content at once.

❓ Can I read files with UTF-8 encoding?

Yes, use new InputStreamReader(new FileInputStream("file.txt"), StandardCharsets.UTF_8) or specify charset in Files.newBufferedReader().

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