Home Java javaTutorial Random Access Files

Random Access Files

Nov 10, 2024 am 08:42 AM

Java allows direct access to any position in a file with the RandomAccessFile class, ideal for manipulating data that needs to be read or written out of order. Unlike the InputStream and OutputStream classes, RandomAccessFile implements the DataInput and DataOutput interfaces, which provide methods for manipulating primitive data types (such as int, double, etc.).

RandomAccessFile Structure and Builder
Constructor:

RandomAccessFile(String nomeArquivo, String acesso)

Copy after login
  • filename: file name.
  • access: defines the type of access ("r" for reading, "rw" for reading and writing).
  • Seek(long position) method: Defines the position of the pointer within the file.
void seek(long novaPos) throws IOException

Copy after login
  • novaPos: Position in bytes from the beginning of the file. After seek, reading/writing happens from the new position.

Code Example: Random Access to Double Values
Below, an example that writes six double values ​​to a file and then reads them at specific positions.

import java.io.*;

class RandomAccessDemo {
  public static void main(String args[]) {
    double data[] = { 19.4, 10.1, 123.54, 33.0, 87.9, 74.25 };
    double d;

    // Abre e usa um arquivo de acesso aleatório
    try (RandomAccessFile raf = new RandomAccessFile("random.dat", "rw")) {

      // Grava os valores no arquivo
      for(int i = 0; i < data.length; i++) {
        raf.writeDouble(data[i]);
      }

      // Lê valores específicos com o método seek()
      raf.seek(0); // Busca o primeiro valor
      d = raf.readDouble();
      System.out.println("Primeiro valor: " + d);

      raf.seek(8); // Busca o segundo valor
      d = raf.readDouble();
      System.out.println("Segundo valor: " + d);

      raf.seek(8 * 3); // Busca o quarto valor
      d = raf.readDouble();
      System.out.println("Quarto valor: " + d);

      System.out.println("\nValores alternados:");
      for(int i = 0; i < data.length; i += 2) {
        raf.seek(8 * i); // Busca o i-ésimo valor
        d = raf.readDouble();
        System.out.print(d + " ");
      }

    } catch(IOException exc) {
      System.out.println("Erro de I/O: " + exc);
    }
  }
}

Copy after login

Code Explanation:
Writing: Double values ​​are written to the random.dat file. As each double occupies 8 bytes, each value starts in multiples of 8 bytes (0, 8, 16, ...).

Reading with seek():

  • First value: Starts at byte 0.
  • Second value: Starts at byte 8.
  • Fourth value: Starts at byte 24 (3rd index, since 8 * 3 = 24).
  • Alternating values: Every 16 bytes (8 bytes between each value), the values ​​are read.

Code Output
Example output:

Primeiro valor: 19.4
Segundo valor: 10.1
Quarto valor: 33.0

Valores alternados:
19.4 123.54 87.9

Copy after login

Important Points:
Positioning with seek(): Defines the position of the pointer to read/write anywhere in the file.
Position Control with Bytes: As each double occupies 8 bytes, we can calculate the position of each value using multiples of 8.
This example is useful for handling large amounts of data efficiently, accessing only the necessary points without traversing the entire file.

Arquivos de acesso aleatório

The above is the detailed content of Random Access Files. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Hot Topics

Java Tutorial
1664
14
PHP Tutorial
1266
29
C# Tutorial
1239
24
Is the company's security software causing the application to fail to run? How to troubleshoot and solve it? Is the company's security software causing the application to fail to run? How to troubleshoot and solve it? Apr 19, 2025 pm 04:51 PM

Troubleshooting and solutions to the company's security software that causes some applications to not function properly. Many companies will deploy security software in order to ensure internal network security. ...

How do I convert names to numbers to implement sorting and maintain consistency in groups? How do I convert names to numbers to implement sorting and maintain consistency in groups? Apr 19, 2025 pm 11:30 PM

Solutions to convert names to numbers to implement sorting In many application scenarios, users may need to sort in groups, especially in one...

How to simplify field mapping issues in system docking using MapStruct? How to simplify field mapping issues in system docking using MapStruct? Apr 19, 2025 pm 06:21 PM

Field mapping processing in system docking often encounters a difficult problem when performing system docking: how to effectively map the interface fields of system A...

How does IntelliJ IDEA identify the port number of a Spring Boot project without outputting a log? How does IntelliJ IDEA identify the port number of a Spring Boot project without outputting a log? Apr 19, 2025 pm 11:45 PM

Start Spring using IntelliJIDEAUltimate version...

How to elegantly obtain entity class variable names to build database query conditions? How to elegantly obtain entity class variable names to build database query conditions? Apr 19, 2025 pm 11:42 PM

When using MyBatis-Plus or other ORM frameworks for database operations, it is often necessary to construct query conditions based on the attribute name of the entity class. If you manually every time...

How to safely convert Java objects to arrays? How to safely convert Java objects to arrays? Apr 19, 2025 pm 11:33 PM

Conversion of Java Objects and Arrays: In-depth discussion of the risks and correct methods of cast type conversion Many Java beginners will encounter the conversion of an object into an array...

E-commerce platform SKU and SPU database design: How to take into account both user-defined attributes and attributeless products? E-commerce platform SKU and SPU database design: How to take into account both user-defined attributes and attributeless products? Apr 19, 2025 pm 11:27 PM

Detailed explanation of the design of SKU and SPU tables on e-commerce platforms This article will discuss the database design issues of SKU and SPU in e-commerce platforms, especially how to deal with user-defined sales...

How to use the Redis cache solution to efficiently realize the requirements of product ranking list? How to use the Redis cache solution to efficiently realize the requirements of product ranking list? Apr 19, 2025 pm 11:36 PM

How does the Redis caching solution realize the requirements of product ranking list? During the development process, we often need to deal with the requirements of rankings, such as displaying a...

See all articles