I/O STREAM (REQUIRED IN THE FINAL)

Transcription

1 I/O STREAM (REQUIRED IN THE FINAL) STREAM A stream is a communication channel that a program has with the outside world. It is used to transfer data items in succession. An Input/Output (I/O) Stream represents an input source or an output destination. A stream can represent many different kinds of sources and destinations, including disk files, devices, other programs, and memory arrays. Streams support many different kinds of data, including simple bytes, primitive data types, localized characters, and objects. Some streams simply pass on data; others manipulate and transform the data in useful ways. No matter how they work internally, all streams present the same simple model to programs that use them: A stream is a sequence of data. READ/WRITE INFORMATION INTO/FROM PROGRAM Reading information into a program. A program uses an input stream to read data from a source, one item at a time:

2 Writing information from a program. A program uses an output stream to write data to a destination, one item at time: The data source and data destination pictured above can be anything that holds, generates, or consumes data. Obviously, this includes disk files, but a source or destination can also another program, a peripheral device, a network socket, or an array. Java encapsulates Stream under java.io package. Java defines two types of streams. They are, 1. Character Stream: It provides a convenient means for handling input and output of characters. Character stream uses Unicode and therefore can be internationalized. 2. Byte Stream: It provides a convenient means for handling input and output of byte. CHARACTER (TEXT) STREAM CLASSES Character stream is defined by using two abstract class at the top of hierarchy, they are Reader and Writer. These two abstract classes have several concrete classes that handle Unicode character

3 SOME IMPORTANT CHARACTER STREAM CLASSES. Reading from text (character) stream. Stream class Description BufferedReader Handles buffered input stream. FileReader Input stream that reads from file. InputStreamReader Input stream that translate byte to character Reader Abstract class that define character stream input Writing to text (character) stream. Stream class Description BufferedWriter Handles buffered output stream. FileWriter Output stream that writes to file. OutputStreamReader Output stream that translate character to byte. PrintWriter Output Stream that contain print() and println() method. Writer Abstract class that define character stream output

4 WHY WE NEED TO USE INPUTSTREAM CLASS Image Source:

5 READING FROM CHARACTER STREAM You have multiple ways to do that. 1. Use BufferReader 2. Use FileReader 3. Use Scanner. Now check the following sections to see the feature of each way. USING BUFFEREDREADER CLASS TO READ CHARACTER STREAM To use the BufferReader with files, let s check the following examples. First, save the lyrics of Hello song inside a text file under the name hello.txt. Save this file inside your project folder, but outside the scr folder. I've been alone with you inside my mind And in my dreams I've kissed your lips a thousand times I sometimes see you pass outside my door Hello, is it me you're looking for? I can see it in your eyes I can see it in your smile You're all I've ever wanted, and my arms are open wide 'Cause you know just what to say And you know just what to do And I want to tell you so much, I love you I long to see the sunlight in your hair And tell you time and time again how much I care Sometimes I feel my heart will overflow Hello, I've just got to let you know 'Cause I wonder where you are And I wonder what you do Are you somewhere feeling lonely, or is someone loving you? Tell me how to win your heart For I haven't got a clue But let me start by saying, I love you Hello, is it me you're looking for? 'Cause I wonder where you are And I wonder what you do Are you somewhere feeling lonely, or is someone loving you? Tell me how to win your heart For I haven't got a clue But let me start by saying I love you

6 READING THE SONG FILE LINE AFTER ANOTHER // Import the exceptions needed import java.io.filenotfoundexception; import java.io.ioexception; //Import the I.O library. import java.io.fileinputstream; import java.io.inputstream; import java.io.inputstreamreader; import java.io.bufferedreader; public class TextFileOperations { public static void main(string[] args) { InputStream fis = null; fis = new FileInputStream("Hello.txt"); catch (FileNotFoundException e) { InputStreamReader isr = new InputStreamReader(fis); BufferedReader br = new BufferedReader(isr); String line; while ( (line = br.readline())!=null) { System.out.println(line); catch (IOException e) {

7 READING THE SONG FILE WORD AFTER ANOTHER Almost, the same code as the one before, put use the split method with line to get the words import java.io.filenotfoundexception; import java.io.ioexception; import java.io.fileinputstream; import java.io.inputstream; import java.io.inputstreamreader; import java.io.bufferedreader; public class TextFileOperations { public static void main(string[] args) { InputStream fis = null; fis = new FileInputStream("Hello.txt"); catch (FileNotFoundException e) { InputStreamReader isr = new InputStreamReader(fis); BufferedReader br = new BufferedReader(isr); String line; while ( (line = br.readline())!=null) { String[] words = line.split(" "); for (int i=0; i < words.length; i++) { System.out.println(words[i]); catch (IOException e) {

8 READING THE SONG FILE CHARACTER AFTER ANOTHER Almost, the same code as the one before, put go over the characters of every word import java.io.filenotfoundexception; import java.io.ioexception; import java.io.fileinputstream; import java.io.inputstream; import java.io.inputstreamreader; import java.io.bufferedreader; public class TextFileOperations { public static void main(string[] args) { InputStream fis = null; fis = new FileInputStream("Hello.txt"); catch (FileNotFoundException e) { InputStreamReader isr = new InputStreamReader(fis); BufferedReader br = new BufferedReader(isr); String line; while ( (line = br.readline())!=null) { // line is the current line String[] words = line.split(" "); //Words is the array of words in line for (int i=0; i < words.length; i++) { String CurrentWord= words[i]; //go over CurrentWord character after another for (int j=0; j < CurrentWord.length(); j++) { System.out.println(CurrentWord.charAt(j)); catch (IOException e) {

9 ANOTHER WAY TO READ A FILE USING FILEREADER. You can use FileReader to read the file content. There is no need to use InputStream, Input StreamReader and BufferedReader as before. But there is a difference. Check the differenc e in the next section. READING THE FILE CHARACTER AFTER ANOTHER import java.io.filereader; public class TextFileOperations { public static void main(string[] args) { FileReader FR = null; FR = new FileReader("hello.txt"); int c; while ((c = FR.read())!= -1) { System.out.print((char)c); catch (FileNotFoundException e) { catch (IOException e) { //guarantee closing the file. finally { if (FR!= null) { FR.close(); catch (IOException e) {

10 READING THE FILE LINE AFTER ANOTHER USING FILEREADER Here you need to use FileReader and BufferedReader import java.io.filenotfoundexception; import java.io.ioexception; import java.io.filereader; import java.io.bufferedreader; public class TextFileOperations { public static void main(string[] args) { FileReader FR = null; BufferedReader BR = null; FR = new FileReader("hello.txt"); BR = new BufferedReader(FR); String line=""; while ((line = BR.readLine())!= null) { System.out.println(line); catch (FileNotFoundException e) { catch (IOException e) { //guarantee closing the file. finally { if (FR!= null) { FR.close(); BR.close(); catch (IOException e) { READING THE FILE WORD BY WORD Use the previous code, but split the line as we did before.

11 DIFFERENCE BETWEEN FILEREADER AND BUFFEREDREADER BufferedReader FileReader 1 BufferedReader is buffered. FileReader is not buffered. 2 BufferedReader reads characters from another Reader (Eg - FileReader) 3 when BufferedReader.read() is called mostly data is read from the buffer. When data is not available in buffer a call is made to read system file and lot of characters are kept in buffer. 4 A BufferedReader enables another Reader to buffer the characters and supports the mark and reset methods. An internal buffer array is created when the BufferedReader is created. As characters from the Reader are read or skipped, the internal buffer is refilled as necessary from the contained Reader, many characters at a time. 5 BufferedReader is much faster as compared to FileReader. 6 Example: As we discussed above that when BufferedReader.read() is called mostly data is read from the buffer. A BufferedReader reads from FileReader, will request lot of data from the FileReader (128 FileReader reads characters from a file. Every time FileReader.read() is called a call is made to read a system file. FileReader.read() reads 2 byte (16-bit) at a time. A FileReader obtains characters from a file in a file system. It does not supports mark and reset methods. FileReader is slower as compared to BufferedReader. Example: As we discussed in point above that every time FileReader.read() is called a call is made to read a system file.

12 characters or so not exact figure). Thus only 2 calls will be made for reading 256 characters from file. Another Example - Real world Example - You must have seen YouTube videos where video is buffered before you actually start watching it, buffering overall improves your video watching experience. A FileReader will make 256 calls for reading 256 characters from file. No buffering will make your videos watching experience a nightmare. Source:

13 Source here.