Java Input and Output Streams: Reading and Writing Primitive Data, Thesis of Java Programming

Download Java Input and Output Streams: Reading and Writing Primitive Data and more Thesis Java Programming in PDF only on Docsity!

Streams and Input/Output Files

Part 3

Mohammed Husain Bohara

Handling Primitive Data Types

 The basic input and output streams provide

read/write methods that can be used for

reading/writing bytes or characters.

 To read/write the primitive data types such as

integers and doubles, we can use filter classes

as wrappers on the existing I/O streams to

filter data to the original stream.

 The two filter classes supported for creating

“data streams” for primitive data types are:

 DataInputStream

 DataOutputStream

Data Input Stream Creation

 Create Input File Stream:

 FileInputStream fis = new FileInputStream(“InFile”);

 Create Input Data Stream:

 DataInputStream dis = new DataInputStream( fis );

 The above statements wrap data input stream (dis) on

file input stream (fis) and use it as a “filter”.

 Methods Supported:

 readBoolean(), readByte(), readChar(), readShort(), readInt(), readLong(), readFloat(), readDouble()

 They read data stored in file in binary format.

Data Output Stream Creation

 Create Output File Stream:

 FileOutputStream fos = new FileOutputStream(“OutFile”);

 Create Output Data Stream:

 DataOutputStream dos = new DataOutputStream( fos );

 The above statements wrap data output stream (dos)

on file output stream (fos) and use it as a “filter”.

 Methods Supported:

 writeBoolean(), writeByte(), writeChar(), writeShort(), writeInt(), writeLong(), writeFloat(), writeDouble()

 They write data to file in binary format.

 How many bytes are written to file when for statements:

 writeInt(120), writeInt(10120)

Writing and Reading Primitive Data

import java.io.; public class ReadWriteFilter { public static void main(String args[]) throws IOException { // write primitive data in binary format to the "mydata" file FileOutputStream fos = new FileOutputStream("mydata"); DataOutputStream dos = new DataOutputStream(fos); dos.writeInt(120); dos.writeDouble(375.50); dos.writeInt('A'+1); dos.writeBoolean(true); dos.writeChar('X'); dos.close(); fos.close(); // read primitive data in binary format from the "mydata" file FileInputStream fis = new FileInputStream("mydata"); DataInputStream dis = new DataInputStream(fis); System.out.println(dis.readInt()); System.out.println(dis.readDouble()); System.out.println(dis.readInt()); System.out.println(dis.readBoolean()); System.out.println(dis.readChar()); dis.close(); fis.close(); } }*

Program Run and Output

 C:\MHB\examples>java ReadWriteFilter

 120  375.  66  true  X

 Display content of “mydata” file (in binary format):

 C:\MHB\examples>type mydata

 x@wx B☺ X

 What is the size of “mydata” file (in bytes)?

 Size of int+double+int+boolean+char

Sequencing and Buffering of Streams

 Buffered streams sit between the program and data source/destination and functions like a filter or support efficient I/O. Buffered can be created using BufferedInputStream and BufferedOutputStream classes.

file1+file2 Buffer Program

file1.dat

Streams

Sequencer

Screen

file2.dat

read()

Buffer

write()

inBuffer

outputBuffer

Example Program

import java.io.; public class CombineStreams { public static void main(String args[]) throws IOException { // declare file streams FileInputStream file1 = new FileInputStream("file1.dat"); FileInputStream file2 = new FileInputStream("file2.dat"); // declare file3 to store combined streams SequenceInputStream file3 = null; // concatenate file1 and file2 streams into file file3 = new SequenceInputStream(file1, file2); BufferedInputStream inBuffer = new BufferedInputStream(file3); BufferedOutputStream outBuffer = new BufferedOutputStream(System.out); // read and write combined streams until the end of buffers int ch; while((ch = inBuffer.read()) != -1 ) outBuffer.write(ch); outBuffer.flush(); // check out the output by removing this line System.out.println("\nHello, This output is generated by CombineFiles.java program"); inBuffer.close(); outBuffer.close(); file1.close(); file2.close(); file3.close(); } }*

Output

 C:\MHB\examples>java CombineStreams

 Hello,  I am C++, born in AT&T.  Hello,  I am Java, born in Sun Microsystems!  Hello, This output is generated by CombineFiles.java program

 If the statement outBuffer.flush() is removed, the

output will be:

 Hello, This output is generated by CombineFiles.java program  Hello,  I am C++, born in AT&T.  Hello,  I am Java, born in Sun Microsystems!

Random Access Files

 So for we have discussed sequential files that are either

used for storing data and accessed (read/write) them in

sequence.

 In most real world applications, it is necessary to

access data in non-sequential order (e.g, banking

system) and append new data or update existing data.

 Java IO package supports RandomAccessFile class that

allow us to create files that can be used for reading

and/or writing with random access.

 The file can be open either in read mode (“r”) or read-

write mode (“rw”) as follows:

 myFileHandleName = new RandomAccessFile (“filename”, “mode”);

 The file pointer can be set to any to any location

(measured in bytes) using seek() method prior to

reading or writing.

Execution and Output

 C:\MHB\examples>java RandomAccess

 true

 X

 File length: 23

Streams and Interactive I/O

 Real world applications are designed to support

interactive and/or batch I/O operations.

 Interactive programs allow users to interact

with them during their execution through I/O

devices such as keyboard, mouse, display

devices (text/graphical interface), media

devices (microphones/speakers), etc..

 Java provides rich functionality for developing

interactive programs.

 Batch programs are those that are designed to

read input data from files and produce outputs

through files.

Reading Integer from Standard Input

 Create buffered reader for standard input by wrapping System.in object:  BufferedReader dis = new BufferedReader(new InputStreamReader(System.in));  Read a line of text from the console  String str = dis.readLine();  Create Tokenens  StringTokenizer st;  st = new StringTokenizer(str);  Convert String Token into basic integer:  int stdID = Integer.parseInt(st.nextToken());

Interactive IO Example

import java.io.*;

import java.util.*;

public class StudentRecord {

public static void main(String args[]) throws IOException {

// Create buffered reader for standard input

BufferedReader dis = new BufferedReader(new InputStreamReader(System.in));

StringTokenizer st;

// reading data from console

System.out.print("Enter Student ID: ");

st = new StringTokenizer(dis.readLine());

int stdID = Integer.parseInt(st.nextToken());

System.out.print("Enter Student Name: ");

String stdName = dis.readLine();

System.out.print("Enter Student Marks: ");

st = new StringTokenizer(dis.readLine());

int stdMarks = Integer.parseInt(st.nextToken());

// write to console

System.out.println("Student details are:");

System.out.println("ID: "+stdID);

System.out.println("Name: "+stdName);

System.out.println("Marks: "+stdMarks);