Text-based application.pptx

8/11/2019 Text-based application.pptx

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Prepared By:Mr. Richard R. BasilioBSECE Dip ICT


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At the end of the lesson, the student shouldbe able to:

Understand the concept of File Handling in Java. Use BufferedReader class for inputing data from

keyboard.

Identify the different IO Streams and apply it to a

programming.

Differentiate Character to Byte Streams IO.


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Reading characters from the keyboard.

Use the System.in byte stream warped in a

BufferedReader object;

Use read method of the BufferedReader object


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Reading an entire line

Use the System.in byte stream warped in a

BufferedReader object;

Use the readLine method;


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Dont forget to import thejava.io package asshown below:

Reading from streams may cause checkedexceptions to occur

Handle these exceptions using try-catch

statements

Or handle by indicating the exception in the

throws clause of the method


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The file class does not provide any opening,processing, or closing capabilities for files but

it is used to obtain information about the file,such as whether it exists or is open, its size,and its most recent modification date.

The File class is a direct descendant of theObject class.


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The class java.io.File can represent either afileor a directory.

Any program that uses the File class must importthis from the java.io package.

The simplest way is to include the whole package

using the statement:

import java.io.*;


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A File object is constructed by a program andused while it is running to manipulate a disk

file and to get information about it. Constructors that can be used to create File

object:

File(String directoryPath)

File(String directoryPath, String filename)

File(File dirObj, String filename)


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Example:File file = new File("in.txt");

File myFile = new File("C:\\Users\\in.txt);


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METHOD PURPOSE

boolean canRead() Returns true if a file is readable

boolean canWrite() Returns true if a file is writable

boolean exists() Returns true if a file existsString getName() Returns the files name

String getPath() Returns the files path

String getParent() Returns the name of the folder in which thefile can be found

long length() Returns the files size

long lastModified() Returns the time the file was last modified;this time is system dependent and should beused only for comparison with other files

times, and not as an absolute time


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Programs read inputs from data sources (e.g.,keyboard, file, network, or another program)

and write outputs to data sinks (e.g., console,file, network, or another program). Inputs and outputs in Java are handled by the

so-called stream.


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A streamis a sequential and continuous one-way flow of information (just like water or oil

flows through the pipe). All Java I/O streams are one-way (except the

RandomAccessFile, which will be coveredlater).


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Two types of streams:

Input stream - comprises of data flowing into a

program. Output stream - comprises of data flowing out of

a program.


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Basic steps for reading a stream: Open a stream from a data source to a Java program.

Read the data while data is available from the data

source. Close the stream.

Basic steps for writing a stream: Open a stream from a Java program to a data source.

Write the data to the data source while data isavailable from the Java program.

Close the stream.


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Open an input/output stream associated witha physical device (e.g., file, network,

console/keyboard), by constructing anappropriate IO-stream object. Read from the opened input stream until

"end-of-stream" encountered, or write to theopened output stream (optionally flush thebuffered output).

Close the input/output stream.


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Java's IO operations is more complicatedthan C/C++, as Java uses 16-bit character set

(instead of 8-bit character set). As a consequence, it needs to differentiate

between byte-based IO and character-based IO.


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Byte streams can be used to read or writebytes serially from an external device.

All the byte streams are derived from the abstractsuperclass InputStream and OutputStream, asillustrated in the class diagram.


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The abstract superclass InputStreamdeclares an abstract method read() to readone data-byte from the input source, andconvert the unsigned byte value (of 0 to 255)to an int. The read() method will blockuntil a byte is

available, an I/O error occurs, or the "end ofstream" is reached.

It returns -1 if for "end of stream", and throws anIOException if it encounters an I/O error.


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Similar to the input counterpart, the abstractsuperclass OutputStreamdeclares an

abstract method write() to write a data-byteto the output sink.

Similar to the read(), two variations of the write()

method to write a block of bytes from a byte-

array buffer are implemented:

public void write(byte[] bytesBuffer) throws

IOException


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Both the InputStream and the OutputStream provides aclose() method to close the stream, which performs thenecessary clean-up operations as well as frees the system

resources. InputStream and OutputStream are abstract

classes that cannot be instantiated. You need to choose an appropriate concrete

implementation subclass (such as FileInputStream andFileOutputStream) to establish a connection to a physicaldevice (such as file, network, keyboard/console).


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The IO streams are often layered or chainedwith other IO steams, for purposes such as

buffering, filtering or format conversion. For example, we can layer a BufferedInputStream

to a FileInputStream for buffered input, and stack

a DataInputStream in front for formatted data

input, as illustrated in the following diagram.


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FileInputStream and FileOutputStream areconcrete implementation to the abstract

class of InputStream and OutputStream, tosupportFile IO. BufferedInputStream &

BufferedOutputStream is commonly appliedto speedup the IO operations.


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The DataInputStream andDataOutputStream can be stacked on top of

any InputStream and OutputStream to filterthe streams so as to perform I/O operationsin the desired data format, such as int anddouble

DataInputStream in = new DataInputStream(new BufferedInputStream( new

FileInputStream("in.txt")));


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Output for the classByteStreamCopyWithOutBuffering


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Output for the classByteStreamCopyWithBuffering


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Java uses 16-bit character set internally,instead of 8-bit character set.

Hence, it has to differentiate between byte-basedIO (for binary data), and character-based text IO.

Other than the unit of operation, character-based

IO is almost identical to byte-based IO.

Instead of InputStream and OutputStream,Reader and Writer shall be used for character-based IO.


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The abstract superclass Readeroperates oncharacters (primitive char or unsigned 16-bit

integer from 0 to 65535), it similarly declares an abstract method read() to

read one character from the input source, and

convert the char to an int; and variations of read()

to read a block of characters.


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Examples:

public abstract int read() throws IOException

public int read(byte[] bytesBuffer, int offset, intlength) throws IOException

public int read(byte[] bytesBuffer) throws

IOException


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The abstract superclass Writersimilarlydeclares an abstract method write(), to write

a character to the output sink.public void abstract void write(int aChar) throws

IOException

public void write(byte[] bytesBuffer, int offset,

int length) throws IOException

public void write(byte[] bytesBuffer) throws

IOException


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The class RandomAccessFileprovidessupports for non-sequential, direct (or

random) access to a disk file. RandomAccessFile is a two-way stream,

supporting both input and output operationswithin the same stream.


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RandomAccessFile can be treated as a hugebyte array.

You can use a file pointer (of type long), similar toarray index, to access individual byte or group ofbytes in primitive types (such as int and double).

The file pointer is located at 0 when the file is

opened.


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It advances automatically for every read and writeoperation by the number of bytes processed.


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Thejava.io package contains aRandomAccessFile class that is used to read

from and write data to anywhere in a file. The RandomAccessFile extends from the

Object class and inherits from the followinginterfaces:

DataOutput

DataInput


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In constructing a RandomAccessFile, you canuse flags 'r' or 'rw' to indicate whether the file

is "read-only" or "read-write" access, Example:

RandomAccessFile f1 = newRandomAccessFile("filename", "r");

RandomAccessFile f2 = newRandomAccessFile("filename", "rw");


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METHOD PURPOSEpublic void seek(long pos) Position the file pointer for

subsequent read/write operation.

public int skipBytes(intbytes)

Move the file pointer forward by thespecified number of bytes.

public long getFilePointer() Obtain the position of the current

file pointer, in bytes, from thebeginning of the file.

public long length() Returns the length of the randomaccess file.


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Create a Java program using the concept ofFile Handling for STI Students Class Card

Evaluation System. The system can acceptstudents information, course and the fourperiodical grades and automaticallycomputes for the GWA. Save the information

in a text file with a file name of student.txtand display all students via reports. Followthe given sample output.


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REQUIREMENTS:

Use Character stream IOfor writing the data into

the textfile and Byte stream IOfor reading and

displaying the data into the console.

Use Scanner Class in entering values from

keyboard.

Add Exception handling for this exercise.


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Documents

Text-based application.pptx