File IO operations with java programming language

File Management in OS

File management includes files and folders creation, copy and paste operations, reading the file and writing into files and deleting the files and folders 

And also reading meta data about files and folders. It may include file free space, occupied space and read/write permissions etc.

These above operations are considered as file management and managed by respective operating system.

GUI that represents Windows File Manager

File Management with Java 

Though Java is platform independent, programming language depends on native file IO resources of operating system.

This is possible with the Java API support. These API are categorized into 2 types.

1. Readers and Writers: Readers and writers does the IO operations, character by character
2. InputStream and OutputStream: Where as InputStream and OutputStream does IO operations byte by byte

Below are simple Java programs that demonstrates different File IO operations.

Program for creating directory

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

public void makeDirectory(String path, String dirName) {

Path dirPath = Path.of(path, dirName);

File dir = new File(dirPath.toString());

boolean isCreated = dir.mkdir();

if (isCreated)

System.out.println("A new directory with the name " + dir.getPath() + " created!");

}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.makeDirectory("e:\\", "students");

}

}

Program for creating file:

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

public void createFile(String dirPath, String dirName, String fileName) throws IOException {

Path filePath = Path.of(dirPath, dirName, fileName);

File file = new File(filePath.toString());

boolean isFileCreated = file.createNewFile();

if (isFileCreated)

System.out.println("A new file with the name " + file.getPath() + " created!");

}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.createFile("e:\\", "students", "student_1");

}

}

Listing all files available in given folder

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

     public void listFiles(String dirPath, String dirName) {
Path dir = Path.of(dirPath, dirName);
File file = new File(dir.toString());
String[] listOfAllFiles = file.list();
System.out.println("List of all Files in the directory/folder - " + dirName + ": ");
for (String fileName : listOfAllFiles) {
System.out.println(fileName);
}
}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.listFiles("e:\\", "pinterest");

}

}

Delete a directory

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

     public void deleteDirectory(String dirPath, String dirName) {

Path dir = Path.of(dirPath, dirName);

File dirToBeDeleted = new File(dir.toString());

if (dirToBeDeleted.exists()) {

boolean isDeleted = dirToBeDeleted.delete();

if(isDeleted)

System.out.println("File deleted!");

else

System.out.println("Could not delete file. File is being used by other program or application.");

}

}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.deleteDirectory("e:\\", "pinterest");

}

}

Read a file content

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

     public void readFile(String dirPath, String dirName, String fileName) throws IOException {

Path filePath = Path.of(dirPath, dirName, fileName);

File file = new File(filePath.toString());

FileReader reader = new FileReader(file.getAbsolutePath());

BufferedReader bufferedRead = new BufferedReader(reader);

String line = null;

while((line = bufferedRead.readLine()) != null) {

System.out.println(line);

}

bufferedRead.close();

}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.readFile("e:\\", "pinterest", "demo.txt");

}

}

Write content into file

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

     public void writeToFile(String dirPath, String dirName, String fileName) throws IOException {

Path filePath = Path.of(dirPath, dirName, fileName);

File file = new File(filePath.toString());

FileWriter writer = new FileWriter(file);

BufferedWriter bufferedWriter = new BufferedWriter(writer);

bufferedWriter.write("allabtjava.com is a web site, has information about java technologies \n");

bufferedWriter.write("This article explains about, files and IO management with java programming language.");

bufferedWriter.close();

}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.writeToFile("e:\\", "pinterest", "demo.txt");

}

}

Demonstration of Java NullPointerException

NullPointerException causes and reasons

Since Java is object oriented programming language, every thing is considered to be an object. and there is always a scope of an object to be null or "No value". 

Since Java supports primitive data types, Java is not considered to be pure Java object oriented programming language. 

Few Notable points about NullPointerException

1. NullPointerExceptions is unchecked exception
2. Please read post Exception handling and java keywords before reading this article
3. Usually if program tries to fetch the value from reference and finds nothing as value, then program throws NullPointerException
4. 'Zero' is not null
5. And empty String is not considered to be null
6. It is not the subclass of RuntimeException class

Demo code that throws NullPointerException 

package com.allabtjava.blog;

public class DemoNullPointerException {

class BeanDemo {

String name;

Integer ID;

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public Integer getID() {

return ID;

}

public void setID(Integer iD) {

ID = iD;

}

}

public DemoNullPointerException() {

}

public void createNullPointerException() {

BeanDemo bean = new BeanDemo();

bean.setName("All about Java!");

System.out.println(bean.getName());

if(bean.getID() == null) {

throw new NullPointerException();

}else {

System.out.println(bean.getID());

}

}

public static void main(String args[]) {

new DemoNullPointerException().createNullPointerException();

}

}

Output

All about Java!

Exception in thread "main" java.lang.NullPointerException

at com.allabtjava.blog.DemoNullPointerException.createNullPointerException(DemoNullPointerException.java:36)

at com.allabtjava.blog.DemoNullPointerException.main(DemoNullPointerException.java:44)

Evolution of Java Programming Language

Evolution of Java:

First of all, The Java programming language and it's tools that we currenly using is not what actually expected. This language started as a project to give solutions for embedded devices, mobile phones and other portable peripherals. 

Initially, the Java was called Oak. 

Why it is Oak first..? and Why it transformed to Java..?

The team of five technocrats including Dr. James Gosling and also known as Dr. Java, together working on a project, which expected to give solutions on embedded devices, portable smart devices and TV Set top Boxes etc. at Sun Micro Systems. 

In the process of achieving this solution, at their breaktime, team used to relax with a coffee by having a glimpse on a scenery of Oak tree next to their facility. 

Once the project has come to conclusion and in the process of giving a title to it, they noticed the Oak trees [Always observing them in their break time], they named this programming language as Oak.

Oak Logo

Why it transformed to Java..?

When the first version of Oak is about to release, The trademark search revealed that Oak is already registered for Oak Technologies company. Then, Java was named to this project.

In the previous paragraph, it is told that, "team used to relax with a coffee by having a glimpse on a scenery of Oak trees next to their facility...". When one of the team members asked to barista, [Usually a coffee bar tender is called with that name] about the name of the coffee bean that she/he serves in the break..? The reply was "Coffee is made of Java Beans.."

Immediately the name of the project confirmed to be Java and first version 1.0 is released into the industry in the year 1994. Rest we know, how Java programming language was developed and evolved into the bigger scope like smart phones, Inbuild JRE into web browsers etc.

The Oracle claims that more than 1 billion devices uses JRE and millions of developers uses Java and it's tools every day.

Java Version 16  is released in March 2021.

Few of the Java products are:

• TV Set top Boxes,
• Android OS
• Realtime JVMs
• Embedded devices
• Almost all Browsers

Java evolved almost 30 years ago since 1994 from it's first version and almost all devices used Java and it's products directly or indirectly in their daily use. Hope Java continues it's charisma infinity days and will do wonders.

Happy Coding..! :)