Ch20 NIO.2

Question 1

What are the key classes in java.nio package?

Answer 1

Question 2

What are these Path methods?
* normalize()
* resolve()

Answer 2

Question 3

What are these Path methods?
* resolveSibling()
* relativize()
* startsWith()

Answer 3

Question 4

What are these Path methods?
* endsWith()
* compareTo()
* toRealPath()

Answer 4

Question 5

How to use Files.getAttribute(Path p, String attribute, LinkOption… options) method to get the last access timestamp of a file?

Answer 5

Question 6

What are the key FileAttributeView classes?

Answer 6

Question 7

What are the key methods of File class?

Answer 7

Question 8

How to make use of File methods in codes?

Answer 8

Question 9

Use Files static methods to check for existence of a file

Answer 9

var b1 = Files.exists(Paths.get(“/ostrich/feathers.png”));
System.out.println(“Path “ + (b1 ? “Exists” : “Missing”));

Question 10

Use Files static methods to test uniqueness of a file

Answer 10

Testing Uniqueness with isSameFile()

public static boolean isSameFile​(Path path, Path path2)
throws IOException

System.out.println(Files.isSameFile(
Path.of(“/animals/monkey/ears.png”),
Path.of(“/animals/wolf/ears.png”)));

Question 11

What Files static methods can be used to create file directory?

Answer 11

Making Directories with createDirectory() and createDirectories()

public static Path createDirectory​(Path dir,
FileAttribute<?>… attrs) throws IOException

public static Path createDirectories​(Path dir,
FileAttribute<?>… attrs) throws IOException

Files.createDirectory(Path.of(“/bison/field”));
Files.createDirectories(Path.of(“/bison/field/pasture/green”));

Question 12

What Files static methods can be used to copy files?

Answer 12

Copying Files with copy()

public static Path copy(Path source, Path target,
CopyOption… options) throws IOException

Files.copy(Paths.get(“/panda/bamboo.txt”),
Paths.get(“/panda-save/bamboo.txt”));

Files.copy(Paths.get(“/turtle”), Paths.get(“/turtleCopy”));

Question 13

What Paths static method can be used to create a Path object?

Answer 13

Path filePathObj = Paths.get(“/panda/bamboo.txt”);

Question 14

How ot use Files static method to copy and replace existing file?

Answer 14

Files.copy(Paths.get(“book.txt”), Paths.get(“movie.txt”),
StandardCopyOption.REPLACE_EXISTING);

Question 15

How to use Files static method to copy data between file and I/O stream?

Answer 15

Copying Files with I/O Streams

public static long copy(InputStream in, Path target,
CopyOption… options) throws IOException

public static long copy​(Path source, OutputStream out)
throws IOException

try (var is = new FileInputStream(“source-data.txt”)) {
// Write stream data to a file
Files.copy(is, Paths.get(“/mammals/wolf.txt”));
}

Files.copy(Paths.get(“/fish/clown.xsl”), System.out);

Question 16

How to use Files static method to copy files into a directory?

Answer 16

Copying Files into a Directory, need to provide a target file name

var file2 = Paths.get(“test.txt”);
System.out.println(“= test path Uri:”+file2.toUri());
// = test path Uri:file:///Users/john.pun/IdeaProjects/java/test.txt
var directory = Paths.get(“enclosure/test3.txt”);
// import static java.nio.file.StandardCopyOption.*;
Files.copy(file2, directory, REPLACE_EXISTING);

var fileResult = Paths.get(“enclosure”).resolve(“test3.txt”);
System.out.println(“= test fileResult path Uri:”+fileResult.toUri());
// = test fileResult path Uri:file:///Users/john.pun/IdeaProjects/java/enclosure/test333.txt

Question 17

How to use Files static method to Move or Rename file or directory?

Answer 17

Moving or Renaming Paths with move()

public static Path move​(Path source, Path target,
CopyOption… options) throws IOException

Files.move(Path.of(“c:\zoo”), Path.of(“c:\zoo-new”));

Files.move(Path.of(“c:\user\addresses.txt”),
Path.of(“c:\zoo-new\addresses2.txt”));

Question 18

How to use Files static method to perform an Atomic Move of file or directory?

Answer 18

Performing an Atomic Move

Files.move(Path.of(“mouse.txt”), Path.of(“gerbil.txt”),
StandardCopyOption.ATOMIC_MOVE);

Question 19

How to use Files static method to delete files or directories?

Answer 19

Deleting a File with delete() and deleteIfExists()

public static void delete(Path path) throws IOException

public static boolean deleteIfExists(Path path) throws IOException

Files.delete(Paths.get(“/vulture/feathers.txt”));
Files.deleteIfExists(Paths.get(“/pigeon”));

Question 20

How to use Files static method to read data from file?

Answer 20

Reading Data with newBufferedReader()

public static BufferedReader newBufferedReader(Path path)
throws IOException

var path = Path.of(“/animals/gopher.txt”);
try (var reader = Files.newBufferedReader(path)) {
String currentLine = null;
while((currentLine = reader.readLine()) != null)
System.out.println(currentLine);
}

Question 21

How to use Files static method to write data to file?

Answer 21

Writing Data with newBufferedReader()

var list = new ArrayList<String>();
list.add("Smokey");
list.add("Yogi");</String>

var path = Path.of(“/animals/bear.txt”);
try (var writer = Files.newBufferedWriter(path)) {
for(var line : list) {
writer.write(line);
writer.newLine();
}
}

Question 22

How to use Files static method to read all lines from a text file to a List of String?

Answer 22

Reading a File with readAllLines()

public static List<String> readAllLines(Path path) throws IOException</String>

var path = Path.of(“/animals/gopher.txt”);
final List<String> lines = Files.readAllLines(path);
lines.forEach(System.out::println);</String>

Question 23

What are the Enum StandardOpenOption options available for opening file?

Answer 23

Enum java.nio.file.StandardOpenOption:

Question 24

What are the common mistakes in using StandardOpenOption properly with Files static methods?

Answer 24

Question 25

What are the rules of the Files createFile method?

Answer 25

Question 26

What are the rules of the Files delete method?

Answer 26

Question 27

What are the rules of the Files createDirectory and createDirectories methods?

Answer 27

Question 28

How to use a File object to determine whether the path it references exists?

Answer 28

var zooFile1=new File(“/home/tiger/data/stripes.txt”);
Systemout.println(zooFile1.exists()); // true if the file exists

Question 29

What is the Files method to search for files?
* Stream<Path> is returned, and is lazily populated
* Must be used within a try-with-resource statement
* It throws IOException
* includes an optional varargs parameter, with options of type FileVisitOption as the last argument (FOLLOW_LINKS)
* maxDepth of 1 means the search for top-level or root folder only, ignore all its subfolders; If we want to search for all folder levels, put Integer.MAX_VALUE.</Path>

Answer 29

Question 30

What is the Files method to list file items in the directory?
* Stream<Path> is returned, and is lazily populated
* Must be used within a try-with-resource statement
* It throws IOException</Path>

Answer 30

Question 31

What is the Files method to Walk a directory tree?
* Stream<Path> is returned, and is lazily populated
* Must be used within a try-with-resource statement
* It throws IOException
* includes an optional varargs parameter, with options of type FileVisitOption as the last argument (FOLLOW_LINKS)
* maxDepth of 1 means the search for top-level or root folder only, ignore all its subfolders; If we want to search for all folder levels, put Integer.MAX_VALUE.</Path>

Answer 31

Question 32

What are the common file attriburtes retrieved by Files.readAttributes()?
Example of codes
try {
BasicFileAttributes attr = Files.readAttributes(path, BasicFileAttributes.class);
FileTime fileTime = attr.creationTime();
} catch (IOException ex) {
// handle exception
}

Answer 32

Question 33

What are the rules of FILES static method copy(Path source, Path target, CopyOption… options)?

Answer 33

Question 34

What are the rules of FILES static method copy(Path source, OutputStream out)?

Answer 34

Question 35

What are the rules of FILES static method copy(InputStream in, Path target, CopyOption… options)?

Answer 35

Question 36

What are the CopyOptions available when the target is a Path?

Answer 36

Question 37

What are the Paths class static utility functions to get path?

Answer 37

Question 38

How to check if two Path objects refer to the same file?

Answer 38

1. If you need the fastest way and know that there are no reparse points and both paths are absolute, it should be safe to use Path.normalize for both paths. You should use File.getAbsolutePath before normalizing if paths may be relative because normalization doesn’t handle it.
2. If you have to be absolutely sure that both paths refer to the same file, use Files.isSameFile.
3. You can also use Path.toRealPath method for resolving any reparse points in path so applying it on both paths should give almost same result as Files.isSameFile but in a different way (maybe slower or faster, also it will not match hardlinks while Files.isSameFile will).