Java File Management

File Management

• This chapter covers java program using hard disks for files and directories.
• During this chapter Input and Output operations and file management are the focus.
• Common classes available in java.io package and java.util package are used.

Computer Files

• Computer systems storage divides into Volatile and Non-Volatile Storage.
• Volatile storage is temporary and when computer shuts down any saved data is lost.
• Java programs save values to random access Memory (RAM).
• Variable objects and associations are saved in RAM.
• When program ends or computer shuts down data is lost.
• Non-volatile storage is permanent and even without power data persists.
• Java programs use permanent storage when saved to disk.
• Computer file is a data set saved on non-volatile device.
• Files exist on hard disks, USB drives, optical disks and compact disks.
• Data saved in file is often known as persistent data.
• Files divide into two types text-file and Binary files.
• Text files have data that any text editor can read because data is encoded by ASCII or Unicode.
• Text files can be data files with traits like payroll files with employee order, name and salary.
• Text files can be program files or application files saving software instructions.
• Gedit vi, pico editors are examples of text files and their extensions are .txt, .java, or .c.
• Binary files have data not encoded as text with binary language meaning data is used with byte form.
• Example extensions are .jpeg, .mp3, and .class.
• Java gives support to various actions on files or directories.
• The list of actions below can be performed on a file through Java Programming.
• Setting file or directory path.
• Opening a file.
• Writing to a file.
• Reading from a file.
• Closing a file.
• Deleting a File.
• Query file attributes.
• Java gives ready inbuilt classes with methods to help complete these tasks.
• This class in java.io package utilizes java stream ideas and gives two different levels of java classes to complete IVO actions on bytes and letters.

Java File Class

• java.io.File class includes File or directory trait data.
• File class can be used to get file/directory qualities.
• Files/directories can be created/renamed/deleted.
• Different file qualities can be found like usage permissions, file size or time of edits.
• Creating file-object related to file class does not mean file or directory exists.
• File object puts the path name or address of hard disk file or directory.
• File class has 30 methods that can be used for various file directory actions.
• File class gives no methods to read from or write to file so many stream classes are available to complete these actions.

File Class Constructors

• Java class links any file by giving it path or giving entire path as word series.
• File-Class can cite any file or directory as below.
• File(String path)
• File(String directory_path, String file_name)
• File(File directory, String file_name)
• For these citations lets take example of "passwd" file available in "/etc" directory in Linux saves user info.
• To show traits you can create JavaFile objects with three styles:
  • File fileobj=new File("/etc/passwd");
  • Giving directory and file name as two different arguments: File fileobj=new File("/etc", "passwd");
  • Using directory links put to dirobj Object: File dirobj = new File("/etc"); File fileobj = new File(dirobj, "passwd").

File Class Methods

• Table 11.1 gives File-Class methods list.
• Method (Method): Description
  • boolean exists(): Returns true if file or directory exists else returns false.
  • boolean isFile(): If is file then true else returns false.
  • boolean isDirectory(): If Directory exists, will return true otherwise false value is returned.
  • boolean isHidden(): If File or directory is hidden then return true.
  • String getAbsolutePath(): Returns entire path of file or directory (absolute path).
  • String getName(): Returns file/directory name cited by object.
  • String getPath(): Returns file or directory path.
  • long length(): Returns number of bytes inside the file
  • String list(): Returns file and directory names available in directory.
  • File listFiles(): Returns array of abstract path names of path ways that show file in directory.
• Now understand name list Program in cited file directory.
• After making file-class object citing certain directory the list() method can give list of files in that directory.
• Program in Codelisting 11.1 shows way of getting list of files available in "/home/Akash/programs/files" directory.
• To count file directory numbers in certain directory a variable is used and the file-class listOfFiles name array is used to save available file objects in directory.

Streams Introduction

• How to edit or indicate language of files has not been learned yet so stream must be understood.
• Java stream-class use to write file or read from file.
• Earlier learned about resources used for Input and output.
• Keyboard is input tool and the monitor is output tool.
• Data can be read or written from a file saved.
• Because of that Hard disk can be Input and output class.
• Many tools with various abilities and providers available in market.
• Hard disks are made by various producers and have different abilities like 500 GB or 1 TB.
• In addition hard disks can be linked with USB or SATA cables.
• Though, when writing program of file input or output operations, Java programmer must not consider hard disk sort or storage ability.
• This can be done because Java provides stream methods.
• Stream is short way to show tool coming from or going to an Input or Ouput tool.
• Stream can be thought of as byte row coming from or going to a Program.
• Write or read Data using streams.
• When writing Data to streams, it is Output streams and can shift Data from program onto hard disk file or to monitor or to computer on network.
• Input stream use is by program by reading data on external tool and can shift Data from keyboard or from file on hard disk to program.
• The key reason behind stream use for Input or output operations is to make program free from the tools used.
• Stream’s two key benefits are below:
  • Programmer does not need to be bothered by tool’s tech data.
  • Program’s source cord can function for many input and output tools without changing any edits.

Java Streams Class

• Lets first try to realize gap between byte and word show to realize Byte-stream and character-stream.
• Lets take number “5” example, as per table 11.2 this number can be shown in two styles:
• Show: Details: Binary Show
  • Number 5(Letter): ASCII value: 53(00110101)
  • Binary number 5: Binary value: 5(00000101)
• Any letter is normally saved as ASCII or Unicode form.
• When putting in calculation reason, its binary value becomes of import.
• One more example the Int i=32 saying reveals ‘i’ name variable as integer type variable, which saves 32 value.
• But 32 can be shown as ‘3’ and ‘2’ as two different letters if writing “Human Beings have 32 teeth” text show is wise which does not do any type of action on number.
• When doing maths actions using, int, float, or double datatypes.
• Java values two stream styles Byte-stream and Character Stream, in which any stream shfts Data file to byte style is byte-stream or binary stream.
• Files prepped with bytecode use binary file as name.
• By chance integer, double, or boolean type variable want to save file and binary file must be used.
• The same can be done by saving Arrays or objects, with Character-stream to make Textfiles and Program cord which can be opened in text editor.
• Java class makes the two gan Character-stream-class and Binary-stream class.
• Character-stream-class available in Java io package completes character data use and binary-stream class in java io package completes binary Data use and figure 11.2 shows stream chart.
• Java stream is classified into two stem styles Input Stream and Output stream in which Input-stream reads Data from file, keyboard.
• Java.io pack holds a variety of stream-class which can make actions of writing and reading.
• To use java.io package program must import.
• Even so, there are many letter and byte action class and most used class will be reviewed.
• The stream is also used so that we are seperate from the tool as it does not need to know what tool is being used.

Character Stream Class

• Character stream-class is java.io package class set that can be used to read/write 16-bit Unicode letter or characters.
• The character-stream-class is back ordered to reader and writer class which is a afile of letter using class and a Writer class which is a file of letter writing class that is a hierarchy of chart of letter stream class.

File Class Inheritance

• Figure 11.3 program shows that java.io reader Class and Java io Writer class, has risen from java.io object class and it is Enstruct Class.
• These Abstract are classes that are not able to be used to make any object but available for methods to function.
• The inputstream reader and buffered Reader in Readers class which are class b
• The file Reader class is inputstreamReader Class Subclass which is subclass.
• Its the same for Output stream writer and printer writer which are Writer Class sub-Class.
• File Writer as Output Stream Writer subclass to perform these tasks that may include method constructs.
• Online access to method constructs is at this url: http://docs.oracle.com/javase/6/docs/api/.

Writer Class

• A writer class is an important and effective way to write character streams and declares object Writer class work and operation that is important for all the character and output streams possible.
• File writer class will be implore din file to perfrom write action in our program.
• The reader Class Method throws a IO exception and can find exception.
• IO exception is exception being tested to care for its ability to cause wrong display.
• Writer Class in Table 11.3 for these ways we can implore its application.
  • Method (Method): Description
  • void close(): stream method
  • void writer (int c): implores 16 bits
  • void writer(String s): write cord string
• This Table contains some of the methods that FileWriter Class contains.
• Output Stream Writer extends writer class and is used to translate the letter streams.
• File writer class, Output stream Writer class and produces charater result from it with constructs :
  • fileWriter(string filepath) throws IOException
  • fileWriter (filefileobj) throws IO exception
  • fileWriter (String filepath, Boolean append) throws IO Exception
• In prior constructors parameter has full address while a file object class describes the file.
• The file writers objects includes methods related to letter connections and writing on append methods.
• Here file writer objects will be created like this: fileWriter fwobject = new filewriter new Filewriter("/java/files/charfile1.text");
• The example with how to write file with code 11.2 to perfrom existing make file with program using write() .

Reader Classes

• For reading reader Class is important to make for character stream and abstreact a reader with its specific function and processes.
• FiileReader Class the input stream and uses to make data action for reading.

InpuStream Class

• inpuStream claas has to extend new object with string form which can perfrom consrtors like methods;
• String =fileParth;
• object = FliteObect, new new FileReader("/java/filers/charFilel.txt")
• Program 11 -3 creates new file for which can import new file from it/ with 3rd line program.
  • Reader class method extracts info from file to make and store.

Bytestream Classes

• We have seen use for letter methods to process the IO pack and used often number with facts and items in file.
• These math operations or programs are done using the aformentined data with biny stream in java. java io object make it easy to store file or in hard drive to write info.