ch14.md

I/O

Files methods

Methods of java.io.File

delete

File notExisting = new File("notExistingFile");
//if the file does not exist, it does not throw an exception!!!
boolean isDeleted = notExisting.delete();
System.out.println(isDeleted); //false

File constructors

Constructor Summary

File vs Path

java.io.File;
java.nio.file.Path;

Path

Path is immutable. This line is ignored:

Path p1;
p1.normalize().relativize(Path.of("/lion"));

Resolve

Calling resolve() with an absolute path as a parameter returns the absolute path.

var p1 = Path.of("/tmp")
var p2 = Path.of("enrico")
var p3 = Path.of("/users")

var resolve = p1.resolve(p2); // /tmp/enrico
resolve = p2.resolve(p1);   //  /tmp
resolve = p1.resolve(p3)  // /users
resolve = p3.resolve(p1)  // /tmp

resolve

relativize

Both paths to be either absolute or relative.

Path path1 = Path.of("tmp/fish.txt"); //relative
Path path2 = Path.of("/user/friendly/birds.txt");  //absolute
// Exception in thread "main" java.lang.IllegalArgumentException: 'other' is different type of Path
System.out.println(path1.relativize(path2));

relativize

toRealPath

It does throw IOException

Path pom = Path.of("pom.xml");

///Users/enrico/github/ocp17/1Z0-829-preparation/pom.xml
System.out.println(pom.toRealPath());

toRealPath() throws IOException if the path does not exist.
toRealPath

toAbsolutePath

It does NOT throw IOException

Path pom = Path.of("pom.xml").toAbsolutePath();

System.in System.out

Do not close!
Because these are static objects, the System streams are shared by the entire application.
The JVM creates and opens them for us. They can be used in a try-with-resources statement or by calling close(), although closing them is not recommended.

IO Classes

Class Name	Level
FileInputStream	low
FileOutputStream	low
FileReader	low
FileWriter	low
BufferedInputStream	high
BufferedOutputStream	high
BufferedReader	high
BufferedWriter	high
ObjectInputStream	high
ObjectOutputStream	high
PrintStream	high
PrintWriter	high

Writer

Writer is an abstract class

Writer writer = new PrintWriter(dest)

Writer in a try-with-resources

I need to declare throws IOException since Writer (abstract) implements Closeable which can throw IOE.

 Writer w = c.writer();
   try (w) {...}

Reader.mark()

Reader.mark(limit)

StringReader.mark()

Marks the present position in the stream. Subsequent calls to reset() will reposition the stream to this point. Params: readAheadLimit – Limit on the number of characters that may be read while still preserving the mark. Because the stream's input comes from a string, there is no actual limit, so this argument must not be negative, but is otherwise ignored.

Serialization

Serializable

If Object implemented Serializable, all objects would be serializable by default, defeating the purpose of having the Serializable interface. Serialization Example

Deserialize Object

try {
    ....  
//this is the proper way to read multiple items from a file
    while(true){
        var obj=ois.readObject();
        if(obj instanceof Person p){
          //do something
        }
    }
}catch(EOFException e){}

Deserialize

Deserialize Object - extends

On deserialization, the JVM will call the no-arg constructor of the first non-serializable parent class it can find in the class hierarchy.

Serialization with Extends

Console

Always checks if console is not null before using it.

Console console = System.console();

wrong way:

Console console = new Console(); //does not compile

Console methods

String input = console.readLine("Type your name: ");
char[] pwd = console.readPassword("Type your pwd: ");

Reader reader = console.reader();
PrintWriter writer = console.writer()

Usage of Console

Stream closed

System.out and System.err when declared within the try with resources can no longer log if used after they are closed.
System.err closed

InputStream

markSupported

if (inputStream.markSupported()){
    inputStream.mark(1);
    }

Usage of Mark