Understanding java streams

 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 your
program

Java 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 are
linked 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 used
to write to a disk file. Java implements streams within class hierarchies defined in the
java.io package.

Modern versions of Java define two types of Streams: byte and
character.
Byte streams provide a convenient means for handling input and
output of bytes.
Byte streams are used, for example, when reading or writing
binary data. They are especially helpful when working with files.
Character streams are designed for handling the input and
output of characters.
Character streams use Unicode and, therefore, can be
internationalized. 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-based
streams simply provide a convenient and efficient means for handling
characters.

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 byte
input streams and OutputStream describes the behavior of
byte output streams.
From InputStream and OutputStream are created several
concrete subclasses that offer varying functionality and
handle the details of reading and writing to various devices,
such as disk files.

Character streams are defined by using two class
hierarchies topped by these two abstract classes:
Reader and Writer.
Reader is used for input, and Writer is used for
output.

Concrete classes derived from Reader and Writer
operate on Unicode character streams.

From Reader and Writer are derived several
concrete subclasses that handle various I/O
situations. In general, the character-based classes
parallel the byte-based classes.

As you know, all Java programs automatically import the
java.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 your
program 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 is
by default the keyboard.
System.err refers to the standard error stream, which is also the
console by default. However, these streams can be redirected to
any 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 {
DataOutputStream dataOut = new DataOutputStream(new
FileOutputStream("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 {

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 BufferedReader
class 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 {
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 newline
fw.write(str);
} while(str.compareTo("stop") != 0);
fw.close();
}
}

import java.io.*;

class DtoS {


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 deserialization
MyClass 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);

}

}

Understanding java streams

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