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.

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