Java I/O: Files and Streams, Schemes and Mind Maps of Java Programming

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LECTURE 09: WORKING WITH

FILES

o File & Stream

o Binary Files

o Text Files

o Serialization

PLAN

o Java views each file as a sequential stream of bytes

o Every operating system provides a mechanism to determine the

end of a file, such as an end-of-file marker or a count of the total

bytes in the file that is recorded in a system-maintained

administrative data structure.

o A Java program simply receives an indication from the operating

system when it reaches the end of the stream

Files and Streams

o File streams can be used to input and output data as bytes or

characters.

o Streams that input and output bytes are known as byte-based streams,

representing data in its binary format.

o Streams that input and output characters are known as character-based

streams, representing data as a sequence of characters.

o Files that are created using byte-based streams are referred to as

binary files.

o Files created using character-based streams are referred to as text

files. Text files can be read by text editors.

o Binary files are read by programs that understand the specific content

of the file and the ordering of that content.

Files and Streams (cont.)

o Java programs perform file processing by using classes from

package java.io.

o Includes definitions for stream classes

• FileInputStream (for byte-based input from a file)
• FileOutputStream (for byte-based output to a file)
• FileReader (for character-based input from a file)
• FileWriter (for character-based output to a file)

o You open a file by creating an object of one these stream classes.

The object’s constructor opens the file.

Files and Streams (cont.)

o Can perform input and output of objects or variables of primitive data

types without having to worry about the details of converting such

values to byte format.

o To perform such input and output, objects of classes ObjectInputStream

and ObjectOutputStream can be used together with the byte-based file

stream classes FileInputStream and FileOutputStream.

o The complete hierarchy of classes in package java.io can be viewed in

the online documentation at

o http://download.oracle.com/javase/6/docs/api/java/io/package-tree.html

Files and Streams (cont.)

o Class File provides four constructors.

o The one with a String argument specifies the name of a file or directory

to associate with the File object.

• The name can contain path information as well as a file or directory

name.

• A file or directory’s path specifies its location on disk.
• An absolute path contains all the directories, starting with the root

directory, that lead to a specific file or directory.

• A relative path normally starts from the directory in which the

application began executing and is therefore “relative” to the current

directory.

Class File

o The constructor with two String arguments specifies an absolute or

relative path and the file or directory to associate with the File object.

o The constructor with File and String arguments uses an existing File

object that specifies the parent directory of the file or directory specified

by the String argument.

o The fourth constructor uses a URI object to locate the file.

• A Uniform Resource Identifier (URI) is a more general form of the

Uniform Resource Locators (URLs) that are used to locate websites.

o Figure 17.2 lists some common File methods. The

o http://download.oracle.com/javase/6/docs/api/java/io/File.html

Class File (cont.)

o FileOutputStream and FileInputStream are two stream objects that

facilitate file access.

o FileOutputStream allows us to output a sequence of bytes; values

of data type byte.

o FileInputStream allows us to read in an array of bytes.

Streams for Low-Level File I/O

Sample: Low-Level File

Output

//set up file and stream File outFile = new File("sample1.data"); FileOutputStream outStream = new FileOutputStream( outFile ); //data to save byte[] byteArray = {10, 20, 30, 40, 50, 60, 70, 80}; //write data to the stream outStream.write( byteArray ); //output done, so close the stream outStream.close();

o FileOutputStream and DataOutputStream are used to output

primitive data values

o FileInputStream and DataInputStream are used to input primitive

data values

o To read the data back correctly, we must know the order of the

data stored and their data types

Streams for High-Level File I/O

• A standard sequence to set up a DataOutputStream object:

Setting up DataOutputStream

File outFile = new File( "sample2.data" ); FileOutputStream outFileStream = new FileOutputStream(outFile); DataOutputStream outDataStream = new DataOutputSteam(outFileStream);

• A standard sequence to set up a DataInputStream object:

Setting up DataInputStream

File inFile = new File( "sample2.data" ); FileInputStream inFileStream = new FileInputStream(inFile); DataInputStream inDataStream = new DataInputSteam(inFileStream);

Sample Input

import java.io.*; class Ch12TestDataInputStream { public static void main (String[] args) throws IOException {

... //set up inDataStream //read values back from the stream and display them System.out.println(inDataStream.readInt()); System.out.println(inDataStream.readLong()); System.out.println(inDataStream.readFloat()); System.out.println(inDataStream.readDouble()); System.out.println(inDataStream.readChar()); System.out.println(inDataStream.readBoolean()); //input done, so close the stream inDataStream.close(); } }