Introduction :-
Hello friends, In this hub, I will be creating and demonstrating the working of File objects in Java. Before we go further, lets go in the basics of importance of files in computers. Generally, data stored in variables and objects are not permanent. They are not persistent. They are normally temporary data which remains in memory as long as the scope of variable. Once a local variable gets out of scope the data is lost. So to keep the data for long time use generally computer uses files. These files are been stored in secondary storage devices such as hard disk, flash drives etc. The data stored in them is permanent.In terms of programming language such as Java, terms like Files and Streams have their own meaning. Java actually sees a file as a stream of bytes which is sequential.
Java provides us a package called as java.io package. This package consist of class File which helps in retrieving information about various files and various directories in disk. Generally they don't provide capabilities such as opening or closing a file and basic processing of a file or directory. However File objects are frequently used with other objects in java.io package to do the above processing of the files and directories.
Creating File Objects :-
File Objects are created with new operator, which calls constructor with four different arguments. One of the constructor requires string passed to it as argument. This string provides the constructor name of the file or directory. The name usually is the path given to constructor where File object can locate the file or directory. The path information provided into the constructor can be either relative or absolute path. The relative path deals with current directory from where the application has began. The absolute path starts from a root directory and proceed to name of the file or directory specified. Another constructor has two arguments passed to it, first argument contains the relative or the absolute path to file directory and the second argument contains the name of the file or directory , which we want to associate to File object. Another constructor with File and String argument is used. Here we use existing File object which points to file or directory specified by the String argument. The last constructor uses the URI as an argument to point to the file or directory. Here by URI we mean Uniform Resource Identifier which are like Uniform Resource Locators. They use URL like pattern to locate the files, e.g. file://C:/java-programs.txt.
Constructors of File :-
File (String path);
File (String path, String name);
File (File obj, String name);
File (URI);
Important methods of File class
Hello friends, In this hub, I will be creating and demonstrating the working of File objects in Java. Before we go further, lets go in the basics of importance of files in computers. Generally, data stored in variables and objects are not permanent. They are not persistent. They are normally temporary data which remains in memory as long as the scope of variable. Once a local variable gets out of scope the data is lost. So to keep the data for long time use generally computer uses files. These files are been stored in secondary storage devices such as hard disk, flash drives etc. The data stored in them is permanent.In terms of programming language such as Java, terms like Files and Streams have their own meaning. Java actually sees a file as a stream of bytes which is sequential.
Java provides us a package called as java.io package. This package consist of class File which helps in retrieving information about various files and various directories in disk. Generally they don't provide capabilities such as opening or closing a file and basic processing of a file or directory. However File objects are frequently used with other objects in java.io package to do the above processing of the files and directories.
Creating File Objects :-
File Objects are created with new operator, which calls constructor with four different arguments. One of the constructor requires string passed to it as argument. This string provides the constructor name of the file or directory. The name usually is the path given to constructor where File object can locate the file or directory. The path information provided into the constructor can be either relative or absolute path. The relative path deals with current directory from where the application has began. The absolute path starts from a root directory and proceed to name of the file or directory specified. Another constructor has two arguments passed to it, first argument contains the relative or the absolute path to file directory and the second argument contains the name of the file or directory , which we want to associate to File object. Another constructor with File and String argument is used. Here we use existing File object which points to file or directory specified by the String argument. The last constructor uses the URI as an argument to point to the file or directory. Here by URI we mean Uniform Resource Identifier which are like Uniform Resource Locators. They use URL like pattern to locate the files, e.g. file://C:/java-programs.txt.
Constructors of File :-
File (String path);
File (String path, String name);
File (File obj, String name);
File (URI);
Important methods of File class
- boolean isFile() :- This method return either true or false. It return true if the File object created by passing a String object to it, is an existing file.
- boolean isDirectory() :- This method return either true or false. It return true if the File object created by passing a String object to it, is an existing directory.
- boolean exists() :- This method returns true if the file / directory represented by the object exists.
- boolean canWrite() :- It returns true if the current application can write the file.
- boolean canRead() :- It returns true if the current application can read the file.
- boolean isAbsolute() :- It returns true if the path specified as String in the File object constructor is absolute.
- String[ ] list() :- If you want directory's content in the form of array of string this method is used. It returns null if the file specified in the argument is not directory.
- long lastModified() :-It provides us with the time, that when a file was last modified.
- long length() :- It returns the length of the file in bytes. If its a directory, an unusual value is returned.
- String getPath() :- It basically returns the path of the file in use.
- String getParent() :- It basically returns the name of parent directory holding the file .
- String getName() :- It return name of the file used at the time of creating File object
- String getAbsolutePath() :- It basically returns the absolute path of file or directory.
- String getCanonicalPath() :- Returns the path of the file object but separators in the path name are system-dependent separators such as / or \.
- Boolean isHidden() :- Returns true if the file is hidden and false otherwise.
- Boolean renameTo(File name) :- Renames the file (or directory) represented by this File instance to the new name specified by Name.
- boolean delete() :- Deletes the file or directory associated with the File object.
- boolean createNewFile() :- Creates a new file with the specified name if it does not exists.
- boolean mkdir() :- Creates a directory by using the abstract path name associated with this File instance.
- boolean mkdirs() :- Creates a directory by using the abstract path name associated with this File instance. Also creates any non-existent parent directories appearing in the given path.
- File [ ] listFiles() :- Returns an array that contains the names of files only contained in the directory represented by this File instance.
