Kurage Notes

Appearance

File IO ​

Getting CWD ​

java
System.getProperty("user.dir")

This will get a string representation of the Curent Working Directory's absolute path.

File & Directory Manipulation ​

https://docs.oracle.com/en/java/javase/22/docs/api/java.base/java/io/File.html

Files ​

Make a new file describer

java
File f = new File("dummy.txt");
  • Create a file describer with relative path of ./dummy.txt
  • File is not created yet

Creating the file as plain file

java
f.createNewFile();
  • Now file is in FS

Check if if file exists

java
f.exists();
// -> boolean

*Using the Utils (Provided in Project 2) ​

As an example, if you want to write a String to a file, you can do the following:

java
Utils.writeContents(f, "Hello World");

Directories ​

Make a new file describer

java
File d = new File("dummy")

Create it as a directory entry

java
d.mkdir();

Serializable ​

Serialization is the process of translating an object to a series of bytes (binary) that can then be stored in the file.

  • C++'s file.write(reinterpret_cast<const char *>(&object, sizeof object))

We can then deserialize those bytes and get the original object back in a future invocation of the program.

  • C++'s file.read(reinterpret_cast<char *>(&object, sizeof object))

To enable an object to be serializable, declare it to be implements Serializable

java
import java.io.Serializable;

public class Model implements Serializable {
  ...
}

Writing the object m to file saveFileName:

java
Model m = ....;
File outFile = new File(saveFileName);
try {
    ObjectOutputStream out =
        new ObjectOutputStream(new FileOutputStream(outFile));
    out.writeObject(m);
    out.close();
} catch (IOException excp) {
    ...
}

Reading the object m from saveFileName:

java
Model m;
File inFile = new File(saveFileName);
try {
    ObjectInputStream inp =
        new ObjectInputStream(new FileInputStream(inFile));
    m = (Model) inp.readObject();
    inp.close();
} catch (IOException | ClassNotFoundException excp) {
    ...
    m = null;
}

*Using the Provided Utils (Provided in Project 2) ​

Serializing with Utils

java
Model m;
File outFile = new File(saveFileName);

// Serializing the Model object
writeObject(outFile, m);

And similarly, deserializing is simply:

java
Model m;
File inFile = new File(saveFileName);

// Deserializing the Model object
m = readObject(inFile, Model.class);