Files

COMP122 Lectures 2021-04-26

File Handles

This is an object that represents a file on the disk (a path in the file system).

java.io.File is used to represent files and provides methods to interact with the file system.

You can call the following methods on a File:

• Deleting
• Renaming
• Check if it exists:
  • Check if it is a file
  • Check if it is a folder

classDiagram
class File{
	+delete() boolean
    +renameTo(File dest) boolean
    +isDirectory() boolean
    +isFile() boolean
    +getPath() String
}

Renaming

import java.io.File;
...

File f1 = new File("output.txt");
File f2 = new File("stuff.out");
if(f1.rename.To(f2)) {
	System.out.println("File rename successful");
else {
	System.out.println("File rename failed");
}

This is not handled using exceptions.

Dealing with Path Differences

Windows uses \ and Unix uses / for directory separators.

To remove this use you can use the separator attribute of the File class:

import java.io.File;

String sep = File.separator;
File fh = new File("data"+ sep + "output.txt");

This will input the appropriate separator for the file-system.

Reading a File with FileReader

The following code will read in a file one character at a time and print it out:

File fileHandler = new File("this-file.txt");
FileReader fileReader = new FileReader(fileHandler);

int i;
while((i = fileReader.read()) != -1) {
	char c = (char)i;
	System.out.print(c);
}

.read() gets the contents one character at a time.

Opening a file that doesn’t exist will give an IOException. This must be done in a try catch block.