Chapter 10 Input Output Streams

Transcription

1 Chapter 10 Input Output Streams ICT Academy of Tamil Nadu ELCOT Complex, 2-7 Developed Plots, Industrial Estate, Perungudi, Chennai Website : contact@ictact.in, Phone : , Fax :

2 Table of Contents 1. Input/output Streams Overview of Streams Bytes vs. Characters Converting Byte Streams to Character Streams File Object Binary Input and Output Print Writer Class Reading and Writing Objects Basic and Filtered Streams... 23

3 Chapter 10 Input Output Streams Page 1

4 Documentation Conventions The following conventions are used in this guide: When you see this This is Recall learning Case study Did you know? Class session Activity Quiz Reference Indented text in different font Code snippet Page 2

5 Chapter 10: Input Output Streams This chapter deals with java s I/O streams. The I/O (input/output) package supports java s basic I/O system. Support for I/O comes from java s core API libraries. Hence this is discussed in detail in this chapter. Page 3

6 1. Input/output Streams 1.1 Overview of Streams Stream: Flow of anything from one point to another point sequentially is called Stream. During program execution, the input flows from file or string or keyboard or mouse to program and output data flows from program to result or screen or memory etc. This type of data flows from input device to program and from program to output device is called data streams or simply streams. Stream is defined as a path along which data flows. Java has two types of streams called input stream and output stream. - Flow of data from data source (file input) to program, is called Input Stream. - Flow of data from program to screen or memory (designation file) called Output Stream. Flow Function: Input Stream File Program Output Stream As the data flows the read & write process occurs continuously. Stream Advantages: - Streams help the user to build dynamic codes to match their type of data transfer. - It simplifies the complex of I/O operations. - The available stream classes functions properly even though new stream classes are invented in future. - The Stream classes works well from one file system based on one stream to another type of file system with another stream. - It helps to serialize objects. Stream class: Page 4

7 Stream classes are present in the java.io package. These classes provide facilities to process all types of data. Stream classes are divided into two groups based on the type of data. 1. Byte stream classes // Using for IO operation in bytes 2. Character stream classes // using for IO operation in characters. Stream Classes Byte Stream Character stream Input Stream Output Stream Reader Class Writer Class A group of classes are used to perform IO operations using various types of devices. The source and designation of data may be memory, a file of a pipe (communication between threads) 1.2 Bytes vs. Characters Byte Stream: Byte stream classes provide facilities to process I/O in bytes. A byte stream can be used with any type of data including binary data. Since the streams are unidirectional, they can transmit data bytes in one direction only. Therefore there are two abstract classes namely Input Stream and Output Stream which are used to read and write process. These abstract classes contain several subclasses to handle different I/O devices. 1. Input Stream Input stream is an abstract class and it is used to stream input data in bytes. It is used for reading the data such as byte and array from an input. An input may be from a file, string or memory. This class contains number of methods used to process input. Here errors may occur, hence it throws IO Exception. Page 5

8 Class methods: int available() - it gives the number of bytes of input currently available for reading. void close() - it is used to close the input source. int read() - it is used to read a byte from Input Stream. int read(byte b[])- it is used to read an array of bytes into byte b array. Filters: Filtering is a process of combining the data bytes into meaningful primitive data type units and monitoring line numbers. The datainputstream class extends from FilterInputStream class and implements from DataInput interface. It has many methods, they are. 1. readint() - read integer value from given input. 2. readlong() - read long value from given input. 3. readfloat() - same as int, long. 4. readline() - read a line from given input. 5. readchar() - read character value from given input. 6. readboolean() - read true or false from given Boolean value Hierarchical structure of Input Stream: Input Stream File Input Stream FilterInputStream StringBufferInputStream ByteArrayInputStream DataInputStream BufferedInputStream LineNumberInputStream 2. Output Stream: Page 6

9 Output stream is an abstract class and it is used to stream output data in bytes. It has many methods used to process output. Here error may occur in the class/method, so it throws I/O Exception. Methods are given below. void close() - it is used to close the stream. void flush() - it is used to clear the output buffers. void writte(int b) - it is used to write a single byte to an output stream. void write(byte b[]) - it is used to write a buffer array in byte b to an output stream. void write(byte b[], int I, int j)-it is used to write j bytes form buffer array b starting from I byte. Hierarchical structure of Output Stream: Output FileOutputStream FilterOutput Stream ObjectOutputStream DataOutput PrintStream BufferedOutput Example Program Page 7

10 import java.io.*; class ioexample public static void main(string[] args) try File ip = new File("input.txt"); File op = new File("output.txt"); FileInputStream fis = new FileInputStream(ip); FileOutputStream fos = new FileOutputStream(op); int i; while ((i = fis.read())!= -1) fos.write(i); fis.close(); fos.close(); catch (FileNotFoundException fnfe) System.err.println("FileStreamsTest: " + fnfe); catch (IOException ioe) System.err.println("FileStreamsTest: " + ioe); Page 8

11 The above program handles the input stream and output stream, when input given is in the form of input.txt file and the output creates new file named as output.txt file. Input file is: Compile the file: Output Page 9

12 Character Stream Classes: Character stream classes are used to process I/O 16 bit Unicode characters. There are two types of character stream classes. They are: Reader class Writer class Reader class: Reader is an abstract class which is used to stream character input data. This class contains number of methods to do input operations. Error may occur in the class, so it throws IOException. This class has many methods, they are. abstract void close() - it is used to close input source. int read() - it is used to return an integer representation of the next available character from the invoking input stream. int read(char b[]) - it is used to read up to length of character into the buffer array b. then it returns the actual number of characters that were successfully read. Page 10

13 abstract int read(char b[], int I, int j)- it is used to ream j characters into buffer b starting from I index. Boolean read() - Example program this method returns true next input is not waiting else false. import java.io.*; public class readexample public static void main(string[] args) throws IOException BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); System.out.println("Enter your text Here : "); String st = in.readline(); System.out.println("Entered Text is: "+st); Output Writer Class Writer is an abstract class and it is used to stream character output data. This class contains number of methods. If error occurs it throws I/O Exception. abstract void close() - it is used to close the output stream. abstract void flush() - it is used to clear the output buffers. Page 11

14 void write(int b) - it is used to write a buffer array of character to an output stream. void write(byte b) - it is used to write a buffer array of characters to an output stream. Void write(byte b[], int I, int j)- it is used to write j characters from buffer b starting from i index character. Example Program import java.io.*; public class writeexample public static void main(string[] args) throws IOException File file=new File("write.txt"); FileOutputStream fop=new FileOutputStream(file); if(file.exists()) String st="writer Class:Writer is an abstract class and it is used to stream character output data."; fop.write(st.getbytes()); fop.flush(); fop.close(); System.out.println("The file has been written and created file name is write.txt "); else System.out.println("This file is not exist"); Output: Page 12

15 Compile File created: write.txt 1.3 Converting Byte Streams to Character Streams Java. Lang Package provides the conversion functionality to convert byte value to String, character or Hexadecimal values.import java.io.*; import java.lang.*; public class convertbyte public static void main(string[] args) throws IOException BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); System.out.println("Enter the Valid Number"); byte b =(byte)4; String str = br.readline(); int i =Integer.parseInt(str); String st = Integer.toHexString(i); System.out.println("Converted Byte to Charecter/String/HexaDecimal:=" + st); Page 13

16 Output Convert character to byte Example import java.io.*; import java.lang.*; public class convertexample public static void main(string[] args) throws IOException BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); System.out.println("Enter your charecters"); String st = br.readline(); char c = st.charat(2); byte b = (byte)c; System.out.println("Converted character value to Byte Value is:=" + b); Page 14

17 Output 1.4 File Object import java.io.*; public class fileexample public static void main(string[] args) throws IOException File f=new File("file.txt"); if(!f.exists()) f.createnewfile(); System.out.println("New File Has been created "file.txt" using File"); Output Page 15

18 Created new file named as file.txt 1.5 Binary Input and Output Byte Stream is used to provide binary Input and Output. It is 8 bit and the streams communicate between the source and the designation file. The input stream is used to read a sequence of bytes and the output stream is used to write a sequence of bytes. 1. All streams are derived from either input or output abstract classes. 2. All methods throw an IOException in both I/O classes. 3. Reader and Writer classes are available. Input Stream This class is an abstract class & it is used to read input from one designation. Methods are used to read inputs: public abstract int read() throws IOException It is used to read the byte data from the input designation. Its return type is int and its range is 0 to 255. The read() method returns a value. This method runs until stream is detected or an exception is thrown. public int read( byte[] b ) throws IOException This method is used to read the array b upto its length. Return byte values or -1 returned. public int available() throws IOException returns the available bytes. public void close() throws IOException Method used to close the Input stream. Page 16

19 Example import java.io.*; class inputexample public static void main(string args[]) throws IOException int i; InputStream is=new FileInputStream("inputexample.java"); System.out.println(" total bytes"+ (i=is.available())); int n=i/40; System.out.println("First" +n+"bytes"); for(int a=0; a<n; a++) System.out.println((char) is.read()); System.out.println("available"+is.available()); System.out.println("reading next"+n); byte b[]=new byte[n]; if(is.read(b)!=n) System.out.println("could not readb"+n); Page 17

20 Output Output Stream This output stream class is also an abstract class. Methods are given below. public abstract void write( int b ) throws IOException It is used to write b as an output of the stream. Lower 8 bit and high 24 bits are lost. public void write( byte[] b ) throws IOException This method writes the array of byte b to the output stream. public int flush() throws IOException flushed in a bytes, which is in buffer out of the stream. public void close() throws IOException Method is closed to the output stream This output stream has two subclasses named as reader and writer. The read() and write() methods waits until the complete process get finished. Eg: input or output. Page 18

21 Example: import java.io.*; class outputexample public static void main(string arg[])throws IOException String s="ict Academy \n"+"java COurse"; byte b[]=s.getbytes(); OutputStream os=new FileOutputStream("ex.txt"); for(int a=0; a<b.length; a+=2) os.write(b[a]); os.close(); OutputStream os1=new FileOutputStream("ex1.txt"); os1.write(b); os1.close(); Output File has been created using OutputStream class: Page 19

22 1.6 Print Writer Class PrintWriter class extends the writer class. public class java.io.printwriter extends java.io.writer PrintWriter class is used to print formatted representations of objects to output stream. It is implements all print classes from PrintStream, it does not have any methods. It is used to print the statements or objects or variables like System.out.println (); PrintWriter p=new PrintWriter(); p.println( welcome ); // System.out.println( Welcome ); Example Program import java.io.*; import java.util.*; public class printwriter1 public static void main(string[] args) StringWriter stw = new StringWriter(); PrintWriter pw = new PrintWriter(stw); Date date = new Date(); Random rd = new Random(date.getTime()); pw.println(rd.nextint()); pw.println(rd.nextlong()); pw.println(rd.nextfloat()); pw.println(rd.nextdouble()); Page 20

23 pw.flush(); if (!pw.checkerror()) System.out.println(stw.getBuffer()); pw.close(); Output 1.7 Reading and Writing Objects Reading and writing objects are serializable objects & it corresponds to read and write text. It uses buffer, & it is good to use(size 8k). It is possible to use abstract class object. It throws IOException and the ClassNotFoundException. Close () method should be implemented in this class or else resource will leak. The flush is automatically called in this class, when it is needed. This stream call closes automatically. Example import java.io.*; public class exampleclass1 public static void main(string[] args)throws IOException Page 21

24 Writer output = null; String text = "ICT Acadamy"; File file = new File("write.txt"); output = new BufferedWriter(new FileWriter(file)); output.write(text); output.close(); System.out.println("Your file has been written"); Output Created file Page 22

25 1.8 Basic and Filtered Streams Class Hierarchy Java IO Input Stream Output Stream FilterInputStream FilterOutputStream DataInputStream BufferedInputStream DataOutputStream PrintStream BufferedOutputStream There are Two classes namely 1. FilterInput Stream 2. FilterOutputStream FilterInputStream This is the base class for all input Stream filters. It overrides all methods of the InputStream class needed to filter data. It provides the additional and chaining functionality for the multiple input streams to be filtered. The constructor of the FilterInputStream is written as: FilterInputStream fis=new FilterInputStream(inputstream in); FilterOutputstream It is the super class of all output stream filters. It overrides all methods from the OutputStream class & it needs to filter the data from output stream. Page 23

26 FilterIntputStream and FilterOutputStream do not perform any filtering themselves; this is done by their subclasses. To improve the performance of these I/O streams, their subclasses BufferedInputStream and BufferedOutputStream are used. Example import java.io.*; class WriteFilter public static void main(string args[]) String st="ict Acadamy welcomes you Java World"; try FileOutputStream fos = new FileOutputStream("filter.txt"); BufferedOutputStream bos = new BufferedOutputStream(fos); bos.write(st.getbytes()); bos.flush(); System.out.print("the data has been written"); catch (Exception e) System.err.println("Exception file: " + e); Page 24

27 Output WriteFilter created file named as filter.txt Exercise 1. Explain about I/O streams. 2. Explain about reading and writing objects Summary In the above chapter we dealt with I/O steams. Hence we are familiar with the following concepts Streams How to convert byte streams to character streams File object Print writerclass Flitered streams Page 25