File. IO and NIO

 1.How to create a file.

package file;

import java.io.File;

public class MyFile {

    public File createFile(String filePath) {
        File myFile = new File(filePath);
        return myFile;
    }
}

package file;

import java.io.File;

public class Main {
    public static void main(String[] args) {
        MyFile file = new MyFile();
        File myFile = file.createFile("test.txt");
    }
}

To create a file in Java, you can use the createNewFile() method. This method returns a boolean value: true if the file was successfully created, and false if the file already exists. Note that the method is enclosed in a try...catch block. This is necessary because it throws an IOException if an error occurs (if the file cannot be created for some reason):

package file;

import java.io.File;
import java.io.IOException;

public class CreateFiles {

    public File create(String fileName) {
        try {
            File myFile = new File(fileName);
            if (myFile.createNewFile()) {
                System.out.println("File created: " + myFile.getName());
            } else {
                System.out.println("File is already exists.");
            }
            return myFile;
        } catch (IOException ex) {
            System.out.println("An error occured.");
            ex.printStackTrace();
            return null;
        }
    }
}
package file;

public class Main {
    public static void main(String[] args) throws Exception{
        CreateFiles myFile = new CreateFiles();
        myFile.create("alibaba.txt");
    }
}
The output is that IDE creates a file. If we run second time the output would be:
"File is alredy exists".
The createNewFile() function creates new empty file and returns true if the abstract file path
does not exist and new file is created. It returns false if the filename is already exists.

2.Write to a file.
package file;

import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;

public class WriteToAFile {

    public void write(String fileName) {
        try {
            FileWriter fw = new FileWriter(fileName);
            fw.write(new Scanner(System.in).nextLine());
            fw.close();
            System.out.println("Successfully wrote to a file.");
        } catch (IOException ex) {
            System.out.println("An error occured.");
            ex.printStackTrace();
        }
    }
}
package file;

import java.io.File;

public class Main {
    public static void main(String[] args) throws Exception{
        CreateFiles myFile = new CreateFiles();
        WriteToAFile fw = new WriteToAFile();
        File myTextFile = myFile.create("alibaba.txt");
        fw.write("alibaba.txt");
    }
}
3.Read from a file.
package file;

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

public class ReadFromAFile {

    public void read(String fileName) {
        try {
            File myFile = new File(fileName);
            Scanner myReader = new Scanner(myFile);
            while (myReader.hasNext()){
                String data = myReader.nextLine();
                System.out.println(data);
            }
            myReader.close();
        }catch (FileNotFoundException ex){
            System.out.println("An error occured");
            ex.printStackTrace();
        }
    }
}
package file;

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

public class Main {
    public static void main(String[] args) throws Exception{
        String fileName = new Scanner(System.in).nextLine();
        CreateFiles myFile = new CreateFiles();
        WriteToAFile fw = new WriteToAFile();
        File myTextFile = myFile.create(fileName);
        fw.write(fileName);
        ReadFromAFile read = new ReadFromAFile();
        read.read(fileName);
    }
}
4.Delete a file.
package file;

import java.io.File;

public class DeleteFile {

    public void delete(String fileName) {
        File myFile = new File(fileName);
        if (myFile.delete()) {
            System.out.println("File has been deleted: " + myFile.getName());
        } else {
            System.out.println("Failed to delete this file.");
        }
    }
}
package file;

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

public class Main {
    public static void main(String[] args) throws Exception{
        String fileName = new Scanner(System.in).nextLine();
        CreateFiles myFile = new CreateFiles();
        WriteToAFile fw = new WriteToAFile();
        File myTextFile = myFile.create(fileName);
        fw.write(fileName);
        ReadFromAFile read = new ReadFromAFile();
        read.read(fileName);
        DeleteFile deleteFile = new DeleteFile();
        deleteFile.delete(fileName);
    }
}

Summary:
package file;

import java.io.*;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class MyFileWriterAndReader {

    public static void writeToFileV1(String text, String fileName) {
        try (FileWriter fw = new FileWriter(fileName);
             BufferedWriter bw = new BufferedWriter(fw)) { // try-with-resources
            bw.write(text);
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    public static void writeToFileV2(String text, String fileName) throws IOException {
        Files.write(Paths.get(fileName), text.getBytes(), StandardOpenOption.WRITE);
    }

    public static String readFromFile(String fileName) throws Exception {
        try (BufferedReader br = new BufferedReader(new FileReader(fileName))){
            StringBuilder content = new StringBuilder();
            String line;
            while ((line = br.readLine()) != null){
                content.append(line);
                }
            return content.toString();
        }
    }

    public static void writeObjectToFile(Object object, String fileName) {
        try (FileOutputStream f = new FileOutputStream(fileName);
             ObjectOutputStream o = new ObjectOutputStream(f)) {
            o.writeObject(object);
        } catch (Exception ex) {
            System.out.println("File not found");
        }
    }

    public static void writeObjectToConsole(Object object) {
        try (ObjectOutputStream o = new ObjectOutputStream(System.out)) {
            o.writeObject(object);
        } catch (Exception ex) {
            System.out.println("File not found");
        }
    }

    public static Object readObjectFromFile(String fileName) {
        try (FileInputStream fi = new FileInputStream(fileName);
             ObjectInputStream oi = new ObjectInputStream(fi)) {
            return oi.readObject();
        } catch (Exception ex) {
            System.out.println("File not found");
            return null;
        }
    }
}