long length() Returns the length of the file. : File « File « SCJP

import java.io.File;
public class MainClass{
  public static void main(String[] argv){
    
    
    File file = new File("c:\\test.dat");
    String[] fileNames = file.list();
    System.out.println(file.length());
  }
}

9.1.File
	9.1.1.	java.io.File class represents the name of a file or directory that might exist on the file system.
	9.1.2.	File: boolean exists() Returns true if the file or directory exists; otherwise returns false.
	9.1.3.	File: String getAbsolutePath() Returns the absolute (that is, not relative) path of the file or directory.
	9.1.4.	File: String getCanonicalPath() Returns the canonical path of the file or directory.
	9.1.5.	File: String getName() Returns the name of the file or directory.
	9.1.6.	File: String getParent() Returns the name of the directory that contains the File.
	9.1.7.	File: boolean isDirectory() Returns true if the File object describes a directory that exists on the file system.
	9.1.8.	File: boolean isFile() Returns true if the File object describes a file that exists on the file system.
	9.1.9.	File: String[] list() Returns an array of the files and directories within the File instance.
	9.1.10.	File: boolean canRead() Returns true if the file or directory may be read.
	9.1.11.	boolean canWrite() Returns true if the file or directory may be modified.
	9.1.12.	boolean createNewFile() Creates a new empty file
	9.1.13.	boolean delete() Attempts to delete the file or directory.
	9.1.14.	long length() Returns the length of the file.
	9.1.15.	boolean mkdir() Attempts to create a directory whose path is described by the current instance of File.
	9.1.16.	boolean renameTo(Filenewname) Renames the file or directory.
	9.1.17.	Creating Files Using Class File