Java Notes

java.io.File

java.io.File is the central class in working with files and directories. Files and directories are both represented by File objects. When a File object is created, the system doesn't test to see if a corresponding file/directory actually exists; you must call exists() to check. See Example - FileTest.java.

File Constructors and Methods

Assume

boolean b;
String s;
String path;     // Relative or absolute path.
String dirpath;  // Relative or absolute path to a directory.
String fname;    // File name
File   f, dir;   // Assume f is a file, dir is a directory.
long   l;
File[] fa;      // Array of File objects.
String[] sa;    // Array of file or directory names.

Constructors
f =	new File(path);	Create File object for default directory (usually where program is located).
f =	new File(dirpath, fname);	Create File object for directory path given as string.
f =	new File(dir, fname);	Create File object for directory.
public static constants
s =	File.separator;	Default path separator (eg, "/" in Unix, "\" in Windows).
Getting Attributes
b =	f.exists();	true if file exists.
b =	f.isFile();	true if this is a normal file.
b =	f.isDirectory();	true if f is a directory.
s =	f.getName();	name of file or directory.
b =	f.canRead();	true if can read file.
b =	f.canWrite();	true if can write file.
b =	f.isHidden();	true if file is hidden.
l =	f.lastModified();	Time of last modification.
l =	f.length();	Number of bytes in file.
Setting Attributes
	f.setLastModified(t);	Sets last modified time to long value t.
b =	f.setReadOnly();	Make file read only. Returns true if successful.
Paths
s =	f.getPath();	path name.
s =	f.getAbsolutePath();	path name (how is it different from above?).
s =	f.getCanonicalPath();	path name. May throw IOException.
s =	f.toURL();	path with "file:" prefix and /'s. Directory paths end with /.
s =	f.toURI();	path with "file:" prefix and /'s. Directory paths end with /.
Creating and deleting files and directories
b =	f.delete();	Deletes the file.
b =	f.createNewFile();	Create file, may throw IOException. true if OK; false if already exists.
b =	f.renameTo(f2);	Renames f to File f2. Returns true if successful.
b =	f.mkdir();	Creates a directory. Returns true if successful.
b =	f.mkdirs();	Creates directory and all dirs in path. Returns true if successful.
Parents and Children
s =	f.getParent();	Name of parent directory.
dir =	f.getParentFile();	File of parent.
sa =	dir.list();	Array of file/directory names in dir.
fa =	dir.listFiles();	Array of files/directories in dir.
fa =	dir.listFiles(ff);	As above after applying java.io.FileFilter ff.