FileApiExample.java

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

public class FileApiExample {
    public static void main(String[] args) throws IOException {
        File file = new File("D:/test-java.txt");
        file.createNewFile();
        
        FileOutputStream outputStream = new FileOutputStream(file);
        outputStream.write("Some string!".getBytes());
        
        if(!file.delete()) {
            System.out.println("Ми не можемо видалити файл, який відкритий (має не закритий I/O stream)");
        }
        
        outputStream.close();
        
        if(file.delete()) {
            System.out.println("Тепер все ок");
        }
    }
}

InputStreamExample.java

import java.io.FileOutputStream;
import java.io.IOException;

public class InputStreamExample {
    public static void main(String[] args) throws IOException {
        FileOutputStream outputStream = new FileOutputStream("D:/test-java.txt");
        String s = "Hello, world!";
        outputStream.write(s.getBytes());
        outputStream.close();
    }
}

OutputStreamIntsExample.java

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

public class OutputStreamIntsExample {
    public static void main(String[] args) throws IOException {
        FileInputStream inputStream = new FileInputStream("D:/test-java.txt");
        Scanner scanner = new Scanner(inputStream);

        int sum = 0;
        while (scanner.hasNextInt()) {
            sum += scanner.nextInt();
        }
        System.out.println(sum);
        inputStream.close();
    }
}

OutputStreamStringExample.java

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

public class OutputStreamStringExample {
    public static void main(String[] args) throws IOException {
        FileInputStream inputStream = new FileInputStream("D:/test-java.txt");
        Scanner scanner = new Scanner(inputStream);

        while (scanner.hasNext()) {
            System.out.println(scanner.nextLine());
        }
        inputStream.close();
    }
}