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Understanding java streams
 

Understanding java streams

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    Understanding java streams Understanding java streams Presentation Transcript

    •  Understand the stream Know the difference between byte and character streams Know Java’s byte stream classes Know Java’s character stream classes Know the predefined streams Use byte streams Use byte streams for file I/O Read and write binary data Use character streams Use character streams for file I/O Object Serialization Object Deserialization
    • A stream is an abstract representation of an input or output device that is a source of,or destination for, data. You can write data to a stream and read data from a stream.You can visualize a stream as a sequence of bytes that flows into or out of yourprogramJava programs perform I/O through streams.A stream is an abstraction that either produces or consumes information. A stream is linked to a physical device by the Java I/O system.All streams behave in the same manner, even if the actual physical devices they arelinked to differ.Thus, the same I/O classes and methods can be applied to any type of device.For example, the same methods that you use to write to the console can also be usedto write to a disk file. Java implements streams within class hierarchies defined in thejava.io package.
    • Modern versions of Java define two types of Streams: byte andcharacter.Byte streams provide a convenient means for handling input andoutput of bytes.Byte streams are used, for example, when reading or writingbinary data. They are especially helpful when working with files.Character streams are designed for handling the input andoutput of characters.Character streams use Unicode and, therefore, can beinternationalized. Also, in some cases, character streams are more efficient than byte streams.At the lowest level, all I/O is still byte-oriented. The character-basedstreams simply provide a convenient and efficient means for handlingcharacters.
    • Byte streams are defined by using two class hierarchies.At the top of these are two abstract classes:InputStream and OutputStream.InputStream defines the characteristics common to byteinput streams and OutputStream describes the behavior ofbyte output streams.From InputStream and OutputStream are created severalconcrete subclasses that offer varying functionality andhandle the details of reading and writing to various devices,such as disk files.
    • Character streams are defined by using two classhierarchies topped by these two abstract classes: Reader and Writer.Reader is used for input, and Writer is used foroutput.Concrete classes derived from Reader and Writeroperate on Unicode character streams.From Reader and Writer are derived severalconcrete subclasses that handle various I/Osituations. In general, the character-based classesparallel the byte-based classes.
    • As you know, all Java programs automatically import thejava.lang package. This package defines a class called System,which encapsulates several aspects of the run-time environment.Among other things, it contains three predefined stream variables,called in, out, and err.These fields are declared as public and static within System.This means that they can be used by any other part of yourprogram and without reference to a specific System object.System.out refers to the standard output stream. By default,this is the console. System.in refers to standard input, which isby default the keyboard.System.err refers to the standard error stream, which is also theconsole by default. However, these streams can be redirected toany compatible I/O device.
    •  BufferedInputStream  InputStream BufferedOutputStream  ObjectInputStream ByteArrayInputStream  ObjectOutputStream ByteArrayOutputStream  OutputStream DataInputStream  PipedInputStream DataOutputStream  PipedOutputStream FileInputStream  PrintStream FileOutputStream  PushbackInputStream FilterInputStream  RandomAccessFile FilterOutputStream  SequenceInputStream
    •  BufferedReader  LineNumberReader BufferedWriter  OutputStreamWriter CharArrayReader  PipedReader CharArrayWriter  PipedWriter FileReader  PrintWriter FileWriter  PushbackReader FilterReader  Reader FilterWriter  StringReader InputStreamReader  StringWriter
    • import java.io.*;class ReadBytes { public static void main(String args[]) throws Exception { byte data[] = new byte[10]; System.out.println("Enter some characters."); System.in.read(data); System.out.print("You entered: "); for(int i=0; i < data.length; i++) System.out.print((char) data[i]); } }
    • class WriteDemo { public static void main(String args[]) { int b; b = X; System.out.write(b); System.out.write(n); } }
    • import java.io.*;class ShowFile { public static void main(String args[]) throws IOException { int i; FileInputStream fin = new FileInputStream(args[0]); do { i = fin.read(); if(i != -1) System.out.print((char) i); } while(i != -1); fin.close(); } }
    • import java.io.*;class CopyFile { public static void main(String args[]) throws Exception { int i; FileInputStream fin = new FileInputStream(args[0]); FileOutputStream fout = new FileOutputStream(args[1]); do { i = fin.read(); if(i != -1) fout.write(i); } while(i != -1); fin.close(); fout.close(); }}
    • import java.io.*;class RWData { public static void main(String args[]) throws Exception { DataOutputStream dataOut = new DataOutputStream(newFileOutputStream("testdata")); int i = 10; double d = 1023.56; boolean b = true; System.out.println("Writing " + i); dataOut.writeInt(i); System.out.println("Writing " + d); dataOut.writeDouble(d); System.out.println("Writing " + b); dataOut.writeBoolean(b); System.out.println("Writing " + 12.2 * 7.4); dataOut.writeDouble(12.2 * 7.4); dataOut.close(); System.out.println(); DataInputStream dataIn = new DataInputStream(new FileInputStream("testdata")); i = dataIn.readInt(); System.out.println("Reading " + i); d = dataIn.readDouble(); System.out.println("Reading " + d); b = dataIn.readBoolean(); System.out.println("Reading " + b); d = dataIn.readDouble(); System.out.println("Reading " + d); dataIn.close(); }}
    • import java.io.*;class CompFiles { public static void main(String args[])throws Exception { int i=0, j=0; FileInputStream f1 = new FileInputStream(args[0]); FileInputStream f2 = new FileInputStream(args[1]); do { i = f1.read(); j = f2.read(); if(i != j) break; } while(i != -1 && j != -1); if(i != j) System.out.println("Files differ."); else System.out.println("Files are the same."); f1.close(); f2.close(); }}
    • import java.io.*;class ReadChars {public static void main(String args[]) throws Exception {char c;BufferedReader br = new BufferedReader( new InputStreamReader(System.in));System.out.println("Enter characters, period to quit.");do {c = (char) br.read();System.out.println(c);} while(c != .);}}
    • import java.io.*;Create BufferedReaderclass ReadLines {public static void main(String args[]) Throws Exception {BufferedReader br = new BufferedReader(new InputStreamReader(System.in));String str;System.out.println("Enter lines of text.");System.out.println("Enter stop to quit.");do {str = br.readLine();System.out.println(str);} while(!str.equals("stop"));}}
    • import java.io.*;public class PrintWriterDemo {public static void main(String args[]) {PrintWriter pw = new PrintWriter(System.out, true);int i = 10;double d = 123.65;pw.println("Using a PrintWriter.");pw.println(i);pw.println(d);pw.println(i + " + " + d + " is " + (i+d));}}
    • import java.io.*;class KtoD {public static void main(String args[]) throws Exception {String str;FileWriter fw = new FileWriter("test.txt");BufferedReader br = new BufferedReader( new InputStreamReader(System.in));System.out.println("Enter text (stop to quit).");do {System.out.print(": "); str = br.readLine();if(str.compareTo("stop") == 0) break;str = str + "rn"; // add newlinefw.write(str);} while(str.compareTo("stop") != 0);fw.close();}}
    • import java.io.*;class DtoS {public static void main(String args[]) throws Exception {FileReader fr = new FileReader("test.txt");BufferedReader br = new BufferedReader(fr);String s;while((s = br.readLine()) != null) {System.out.println(s);}fr.close();}}
    • class MyClass implements Serializable { double id; String name; String course; public MyClass(double i, String n, String c) { id=i; name=n;course=c; } public String toString() { return “ID: " + id + “nNAME: " + name + “nCOURSE: "+ course; }}
    • import java.io.*; public class SerializationDemo { public static void main(String args[]) throws Exception{// Object serialization MyClass object1 = new MyClass(2342, “Shahjahan”, “Java”); System.out.println("object1: " + object1);FileOutputStream fos = new FileOutputStream("serial");ObjectOutputStream oos = new ObjectOutputStream(fos);oos.writeObject(object1);oos.flush();oos.close();}
    • // Object deserializationMyClass object2;FileInputStream fis = new FileInputStream("serial");ObjectInputStream ois = new ObjectInputStream(fis);object2 = (MyClass)ois.readObject();ois.close();System.out.println("object2: " + object2);}}
    • import java.util.zip.*;import java.io.*;public class GZIPcompress {public static void main(String[] args)throws IOException {BufferedReader in = new BufferedReader( new FileReader(args[0]));BufferedOutputStream out = new BufferedOutputStream( new GZIPOutputStream(new FileOutputStream("test.gz")));int c; while((c = in.read()) != -1) out.write(c);in.close(); out.close();BufferedReader in2 = new BufferedReader( new InputStreamReader(new GZIPInputStream( new FileInputStream("test.gz"))));String s; while((s = in2.readLine()) != null) System.out.println(s);}}