Java File Example

1: How to reaad text file
public class javareadfile {

    public static void main(String[] args) throws FileNotFoundException, IOException {
         String line = null;
        BufferedReader br = new BufferedReader(new FileReader("file.txt"));
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }
                br.close();
    }
}
2: How to read and write text files
public class myFile {
    public static void main(String[] args) throws IOException{
        // write to text file
        ArrayList<String> lines = new ArrayList<String>();
        lines.add("Сайн уу? world");
        lines.add("This is дараагийн мөр");
        Path pathtoFile = Paths.get("file.txt");
        Files.write(pathtoFile, lines, StandardCharsets.UTF_8, StandardOpenOption.APPEND);
        // read from text file
        List<String> line2 = Files.readAllLines(pathtoFile, StandardCharsets.UTF_8);
        for(String l : line2)
            System.out.println(l);
    }
}
3: How to copy, move and delete files in Java

    public static void main(String[] args) throws IOException{
        // write to text file
        ArrayList<String> lines = new ArrayList<String>();
        lines.add("Сайн уу? world");
        lines.add("This is дараагийн мөр");
        Path pathtoFile = Paths.get("file.txt");
        Files.write(pathtoFile, lines, StandardCharsets.UTF_8, StandardOpenOption.APPEND);
        // read from text file
        List<String> line2 = Files.readAllLines(pathtoFile, StandardCharsets.UTF_8);
        for(String l : line2)
            System.out.println(l);
        // file exists?
        System.out.println("file exists?: " + Files.exists(pathtoFile));
        Path pathtoFile2 = Paths.get("file2.txt");
        // move file
        Files.move(pathtoFile, pathtoFile2, StandardCopyOption.REPLACE_EXISTING);
        System.out.println("file exists?: " + Files.exists(pathtoFile));
        // copy file
        Files.copy(pathtoFile2, pathtoFile);
        // delete file
        Files.delete(pathtoFile);
        Files.delete(pathtoFile2);          
    }
}
4: How to get free, available and total disk space in Java
public class javadisk {
    public static void main(String[] args) throws IOException{
        FileStore fs = Files.getFileStore(Paths.get("c:/"));
        long totalSpaceInBytes = fs.getTotalSpace();
        long freeSpaceInBytes = fs.getUsableSpace();
        long usedSpaceInBytes = totalSpaceInBytes - freeSpaceInBytes;
        System.out.println("total space in GB: " + (totalSpaceInBytes/1024/1024/1024));
        System.out.println("free space in GB: " + (freeSpaceInBytes/1024/1024/1024));
        System.out.println("used space in GB: " + (usedSpaceInBytes/1024/1024/1024));
    }
}