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File Object

layout: default title: File Object

You can use a File object to represent the path and filename of file.

  • You can construct a File object using its relative or absolute pathname.
File f = new File("./input.txt");

  • The file's length, full directory location, and associated information can be retrieved from the File object.

  • getName()

  • getCanonicalPath()

  • length()

  • The platform-specific path separator can also be used for more generic naming of paths.

File f = new File("." + File.separator + "input.txt");

A File does not need to represent a file stream that is currently open.

import java.io.File;
import java.io.IOException;

public class FileInfo {
  public static void main(String[] args) {
    File f = new File("employee.txt");
    System.out.printf("The length of %s is %d bytes.%n",
        f.getName(), f.length());

    try {
      System.out.printf("%s has a full path of %s.%n",
          f.getName(), f.getCanonicalPath());
    }
    catch (IOException e) {
      System.out.println(e);
    }
  }
}

Practice Exercise

When you run a Java program in Eclipse, its current working directory at runtime is the top-level folder of the project itself, not the package, src, or bin directory. Paths to files will be relative to the project directory.

Drill

Run FileInfo.

Many java.io methods take File object parameters.

  • For convenience, some methods and constructors take filename String arguments which they convert internally to File objects.

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