Java.io.RandomAccessFile Class Method Import RandomAccessFile in Java with Examples

Updated: 06/Feb/2025 by Computer Hope

Introduction

In Java, the RandomAccessFile class allows reading and writing data to a file at any position. This feature makes it ideal for applications that require efficient file manipulation. Unlike FileWriter and FileReader, RandomAccessFile provides both read and write capabilities and enables seeking a specific position within a file.

In this tutorial, we will explore how to use RandomAccessFile to write and read data in a file using Java, along with practical examples.

Understanding RandomAccessFile in Java

The RandomAccessFile class in Java's java.io package provides methods such as:

• writeInt(int value) – Writes an integer to the file.
• writeDouble(double value) – Writes a double value to the file.
• writeBoolean(boolean value) – Writes a boolean value to the file.
• readInt() – Reads an integer from the file.
• readDouble() – Reads a double value from the file.
• readBoolean() – Reads a boolean value from the file.
• seek(long position) – Moves the file pointer to a specified position.

Example 1: Writing and Reading Data Using RandomAccessFile

This example demonstrates writing an integer, double, and boolean value to a file using writeInt(), writeDouble(), and writeBoolean(). It then reads and prints the data using readInt(), readDouble(), and readBoolean().

import java.io.*;

class FileExample7 {
    public static void main(String args[]) {
        try {
            RandomAccessFile rac = new RandomAccessFile("d:/assignments/mydata.dat", "rw");
            
            // Writing data to file
            rac.writeInt(1024);
            rac.writeDouble(456.45);
            rac.writeBoolean(true);
            
            System.out.println("File size is " + rac.length() + " bytes");
            
            // Reading data from file
            rac.seek(0);
            int intValue = rac.readInt();
            double doubleValue = rac.readDouble();
            boolean booleanValue = rac.readBoolean();
            
            System.out.println("Integer value: " + intValue);
            System.out.println("Double value: " + doubleValue);
            System.out.println("Boolean value: " + booleanValue);
            
            rac.close();
        } catch (Exception ex) {
            System.out.println("Error in writing or reading Object");
        }
    }
}

Example 2: Storing and Retrieving Prime Numbers

This example demonstrates how to write prime numbers to a file and retrieve a specific prime number based on user input.

import java.io.*;
import java.util.*;

class FileExample8 {
    public static void main(String args[]) {
        try {
            RandomAccessFile rac = new RandomAccessFile("d:/assignments/primenos.dat", "rw");
            Scanner kb = new Scanner(System.in);
            
            System.out.println("Enter a number:");
            int n = kb.nextInt();
            
            // Writing prime numbers to file
            first:
            for (int i = 2; i <= n; i++) {
                for (int j = 2; j <= i - 1; j++) {
                    if (i % j == 0) continue first;
                }
                rac.writeInt(i);
            }
            
            System.out.println("Enter a position:");
            int pos = kb.nextInt();
            int count = (int) (rac.length() / 4);
            
            if (pos > count) {
                System.out.println("Invalid position");
            } else {
                rac.seek((pos - 1) * 4);
                int primeNo = rac.readInt();
                System.out.println("Prime number at position " + pos + " is " + primeNo);
            }
            
            rac.close();
        } catch (Exception ex) {
            System.out.println("Error in writing or reading Object");
        }
    }
}

Key Takeaways

• RandomAccessFile allows both reading and writing operations at any position within a file.
• Methods such as seek() enable random access, making it more efficient than sequential file readers and writers.
• writeInt(), writeDouble(), and writeBoolean() store different types of data.
• readInt(), readDouble(), and readBoolean() allow retrieving the stored data.
• Useful for applications requiring quick access to specific file data, such as databases, index-based file processing, and caching systems.

Conclusion

The RandomAccessFile class in Java is a powerful tool for handling files efficiently. It enables both sequential and random file access, making it a preferred choice for working with structured file storage and retrieval. By using seek(), you can quickly navigate through large files, enhancing performance compared to traditional file handling techniques.

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