Bài giảng Phát triển phần mềm phân tán - Bài 11: Input and output operations - Vũ Thị Hương Giang

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LESSON XI.

Input and Output Operations

Vu Thi Huong Giang

SoICT (School of Information and

Communication Technology)

HUST (Hanoi University of Science

and Technology)

Objectives

• Become familiar with the concept of an I/O

stream

• Understand the difference between binary files

and text files

• Learn how to read data from a file

• Learn how to save data into a file

Content

I. Basic input and output

II. File Manipulation

III.Input and Output with Scanner and

printf

I. Basic input and output

1. Overview

2. Model to do I/O

1. Overview – I/O

• I/O = Input/Output

• In this context it is input to and output from

programs

• Input can be from keyboard or a file

• Output can be to display (screen) or a file

• Advantages of file I/O

– permanent copy

– output from one program can be input to another

– input can be automated (rather than entered manually)

1. Overview-Streams

• All modern I/O is stream-based

• Stream: an object that either delivers data to its

destination (screen, file, etc.) or that takes data from

a source (keyboard, file, etc.)

– it acts as a buffer between the data source and destination

• Input stream: a stream that provides input to a

program

– System.in is an input stream

• Output stream: a stream that accepts output from a

program

– System.out is an output stream

• A stream connects a program to an I/O object

– System.out connects a program to the screen

– System.in connects a program to the keyboard

1. Overview - Package java.io

• This package offers the below classes that handle

Java I/O

java.lang.Object

InputStream

OutputStream

FileInputStream

FileOutputStream

Reader

Writer

InputStreamReader

BufferedReader

OutputStreamWriter

PrintWriter

FileReader

IOException

FileWriter

File

I. Basic input output

1. Over view

2. Model to do I/O

import java.io.*;

• Open the stream

• Use the stream (read, write, or both)

• Close the stream

Opening a stream

• There is data external to your program that you

want to get, or you want to put data somewhere

outside your program

• When you open a stream, you are making a

connection to that external place

• Once the connection is made, you forget about the

external place and just use the stream

Example of opening a stream

• A FileReader is used to connect to a file that will be

used for input:

FileReader fileReader =

new FileReader(fileName);

• The fileName specifies where the (external) file is to

be found

• You never use fileName again; instead, you use

fileReader

Using a stream

• Some streams can be used only for input, others

only for output, still others for both

• Using a stream means doing input from it or output

to it

• But it’s not usually that simple--you need to

manipulate the data in some way as it comes in or

goes out

Example of using a stream

int charAsInt;

charAsInt = fileReader.read( );

• fileReader.read():

– reads one character

– returns it as an integer,

– returns -1 if there are no more characters to read

• You can cast from int to char:

char ch = (char) fileReader.read( );

Manipulating the input data

• BufferedReader class:

– convert integers to characters

– read whole lines

BufferedReader bufferedReader =

new BufferedReader(fileReader);

Reading lines

String s;

s = bufferedReader.readLine( );

• A BufferedReader will return null if there is

nothing more to read

Closing

bufferedReader.close( );

• You should not have more than one opened

stream on the same file.

• You must close a stream before you can open it

again

• Java will normally close your streams for you

when your program ends, but it isn’t good style to

depend on this

II. File manipulation

1. Text files versus binary files

2. File Class

3. Text files

4. Byte stream files

5. Object stream files-Serialization

1. Binary Versus Text Files

• All data and programs are ultimately just zeros and ones

– each digit can have one of two values, hence binary

– bit is one binary digit

– byte is a group of eight bits

• Text files: the bits represent printable characters

– one byte per character for ASCII, the most common code

– for example, Java source files are text files

– so is any file created with a "text editor"

• Binary files: the bits represent other types of encoded

information, such as executable instructions or numeric data

– these files are easily read by the computer but not humans

– they are not "printable" files

• actually, you can print them, but they will be

unintelligible

• "printable" means "easily readable by humans when

printed"

Java: Text Versus Binary Files

• Text files are more readable by humans

• Binary files are more efficient

– computers read and write binary files more easily than

text

• Java binary files are portable

– they can be used by Java on different machines

– Reading and writing binary files is normally done by a

program

– text files are used only to communicate with humans

II. File manipulation

1. Text files versus binary files

2. FileClass

3. Text files

4. Byte stream files

5. Object stream files-Serialization

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