streams

Stream: i) Constant flow of water is called as stream. ii) In computer stream is a flow of data items of unlimited length. A Set of classes is used by some programmers or some program users, memory as its source as well as its destination. IO Stream (or) java.io package consists of a set of classes and interfaces which can be used by the java programmers to read the (take) data from multiple input sources and write the data to different destinations. IS-->Input Source OD-->Output Destination
InputStream & OutputStream An abstract method can be called from the concrete method:
Example:
package basics;

abstract class IStream{
abstract int read();
void read(int k,int i){
for(int n=0;n<i;n++)
k=read();
System.out.println(k);
}
}
public class Impl extends IStream
{
int read()
{
return 10;
}
public static void main(String arg[])
{
Impl i=new Impl();
i.read(10,20);
}
}
In input & output Streams library we have two abstract classes: (i) InputStream (ii) OutputStream, which are extended by the sub-classes to provide the implementation of reading from multiple sources & writing multiple destinations. The advantage of the design of having the super-classes Input and Output Streams is, any one can provide their own implementation of a new class to read or write data extending. After Java1.0,JavaSoft has developed reader-->read character by character. writer-->write character by character. The classes (or) the sub-classes of I/O Streams allow the programmer to read or write byte by byte Format. From Java1.1 Onwards JavaSoft has provided another set of classes to read and write character data .The Super-classes for the set of classes that reads and writes character data are: Reader and Writer. JavaSoft Followed a very simple technique naming convention to easily identify the name of the classes that acts as input stream (or) reader.
end of Stream ---> End is represented by special # -1.



Our program is a motor
Our data is a well
I/O stream is a pipe
File is a tank
Filter: Filter is used to perform some sort of conversion as per our requirement.(convert
the way the data can be understood by the programmer).Filter gets the data in one form i.e. byte by byte and converts it into integer/float/long or any other data types. Data requires filtering action. Type of filtering depends upon the developer’s requirement. Filtering may be in the outside i.e. output side or in the input side. When we write a program in java or any kind of languages, we need to take input and produce an output. Using the sub classes of input and output streams, we can read the data byte by byte or write the data byte by byte. But in some cases it would be convenient for the java programmer to read the data in a different format. In order to allow this, JavaSoft has designed two different classes,
1. FilterInputStream 2. FilterOutputStream
Subclasses of FilterInput/output streams are used to perform filtering actions.




every filter requires another stream. Any FilterInputStream requires some other InputStream as a parameter and any FilterOutputStream requires some other output stream as a parameter.
In the Input/Output classes we have two classes with the name
ByteArrayInput/OutputStreams, which are used to represents a memory as the source and
memory as the destination.
Source file is replaced by memory.
* FileInputStream requires file as input.
* ByteArrayInputStream requires memory as input.

Example:
class iostream
{
public static void main(String args[])
{
byte c[]={22,23,24,25,.....,32};
InputStream in=new ByteArrayInputStream(c);
/* creation of file InputStream is different from that of ByteArrayInputStream */
in.mark(10); //read limit is 10
System.Out.println("is mark supported: "+in.markSupported());
/* markSupported returns true/false, if it is true, this will support the marks
(bookmarks)
otherwise this will not support.*/
System.Out.println("next available byte is="+in.read());
// this returns the next available byte in an array.
byte b[]=new byte[20];
in.read(b,0,3);
int i;
for(i=0;i<3;i++)
{
System.Out.println(b[i]," ");
System.Out.println();
in.reset();
System.Out.println("bytes read are: "+in.read(b,0,3));
System.Out.println("in.available()" +in.available());
System.Out.println(in.read());
}
/* InputStream.available() returns the number of bytes available in the next read
call */ }

When we use multi byte read, the return type value indicates the no of bytes read and in
some cases it returns -1 to indicate the end of stream is reached.
-1 returns 255
Byte --->127 should be a negative value.
When we use InputStream.read(), the read method converts a negative byte value into a
positive value i.e., greater than 127.
[-1=255, -2=254, -3=253, ..............., -128=127]
* When we use single byte read in the InputSteram, all the negative byte values converted
into positive integers by using the below formula.
* As a java programmer we need to check always the return values of single byte read
and then apply appropriate logic to get actual values read from the stream.
* When we use multi byte read, the values are returned as it is. In case of single byte
read, the above logic is used to differential between a byte value -1 and the end of stream
-1 value.
In case of InputStream which supports the mark operation, we can use the methods:
1. mark() --> to place a bookmark
2. reset() --> to come back to the bookmark
3. readLimit() --> to limit the bytes read
4. skip(n) --> to skip n number of bytes
note: we should not use the mark and reset operations on the stream which does not
return true for marksupported method. In some of the streams it may be possible to reset
back after crossing the readlimit. But it is always recommended to reset back before
crossing the readlimit.
* In case of InputStream we can use the mark method to put a single mark.
* In.available() returns number of bytes are available to the next read call and in some
cases In.available() may return a value x, but when we execute In.read() as shown, it
may return a value greater than x if the input is the network program.
In.available();
/* if there are 10 bytes in an array */
In.read(b.0,x+99);
/* here it is should return 10, but it is returning the value greater than x.*/
* In case of ByteArrayInputStream where the total data available is the memory itself. we
can able to predict the return values for available methods.
* Experiment with ByteArrayInputStream which allows us to write the output to memory
itself.
We can use FilterStreams to compress and uncompress the data.
The other filters allow us to read byte by byte and convert them as integers, strings
(primitive data types). A java programmer can use a filter and write java primitive data
types which will be converted to bytes.



There are standard algorithms to compress and uncompress the data. ex: WinZip
java.util.zip --- package
Inflator() -- expands the data Deflator() -- compress the data
If you read the data from compressed file while InputStream is connected to the filter,
then some data is not available to the FilterStream. If you want to read the data from
FilterStream you should not get the complete data. If you want the data you must read
either from FileInputStream or from the Filter. But don’t read the data from the two.
ex: /* program to uncompress the compressed data */
class uncompress
{
//Filter on the input side
public static void main(String args[])throws Exception
{
FileInputStream fis=new FileInputStream("com.bmp");
FileOutputStream fos=new FileOutputStream("uncom.bmp");
InflaterInputStream iis=new InflaterInputSteream("fis");
int data;
while((data=fis.read())!=-1)
{
fis.write(data);
}
fis.close();
}
}
/* program to compress the uncompressed file */
class compress
{
//Filter on the output stream
public static void main(String args[])throws Exception
{
FileInputStream fis= new FileInputStream("uncom.bmp:);
FileOutputStream fos=new FileOutputStream("com.bmp");
DeflaterOutputStream dos=new DeflaterOutputStream("fos");
int data;
while((data=fos.read())!=-1)
{
fos.write(data);
}
fos.close();
}
}
note: experiment with the compressed file by compressing it again.

* We have different FilterStreams available which allows us to read the data in java
primitive data types format and write the data in java primitive data types format.
DataInputStreams are the subclasses of filter input/output streams
Data Input/Output Streams allows us to read the data using java primitive data type
format and writing java primitive data type format.
* Using DataInputStream we can convert the underlying ByteStream to java primitive
datatypes
Using DataOutputStream we can write the data using java primitive datatypes which will
be converted by DOS as bytes and they are written to the underlying stream.
Data input/output example:
We can not use the following methods because they are not part of FileInputStreams
contract.
System.Out.println(fis.readInt());
System.Out.println(fis.readFloat());
System.Out.println(fis.reset());
/* how the data input/output stream works */
ex: ByteArray as input parameter to the inputstream
class iostreams
{
public static void main(String args[])throws Exception
{
byte c1={22,23,24,.....,32};
byte c2={2,3,4,5,6,7,8,9,0,1,2};
InputStream in=new ByteInputStream(c1,0,10);
FileInputStream fis=new DataInputStream(in);
System.out.println(fis.read());
DataInputStream dis=(DataInputStream)fis;
fis.mark(10);
System. Out.println(dis.readInt());
fis.reset();
System.Out.println(dis.readFloat());
System.Out.println(dis.readInt());
System.Out.println(dis.readDouble());
}
}
note: in this example we are reading 10 bytes from an input stream. From this 4 bytes
are used to convert to float and 4 bytes are to double data type we will get an error saying
that EOF. This is occurred because the remaining bytes are 2 only. But we need 8 bytes
to convert double data type.
* observe the output the output will be displayed in a binary form.
output: 22
387455258
1.2913426 to -22
Exception in thread "main" java.io.EOFException
The data input stream takes the appropriate number of bytes from the underlying stream
and converts it into java primitive data type. For example, to create an integer,DataInputStream
takes 4 bytes from the underlying stream and converts into integers.
Incase of DataOutputStream the DataOutputStream can be fed with any outputstream as a
parameter and we can apply the methods writeInt(), writeFloat().

Print Stream:
* Depending on the configuration of o\s we have certain limit on number files that can be
used by a particular program. so it is always advisable to close the files after using the
files.
X Y in UNIX o/s X|Y means
stdout of first program is the stdin of second program.
When we use a pipe symbol between two programs in unix o/s, the unix o/s is responsible
to connect stdOut of first program to stdIn of second program.

* Print Streem provides the methods like print() and println().
* Nulloutput-> It takes some bytes, and writes nothing (or) not stored any where.
* By default printstream connected to the FileDescriptor (stdout). Which is by default connect to the monitor.
Ex:- /* Print Stream with Nullop Example*/
class iostreamg
{
public static void main(String args[])throws Exception
{
nullop nop=new nullop();
PrintStream ps=new PrintStream(nop);
System.out.println("Before setting the new out Stream");
System.setout(ps);
System.out.println("After setting the new out stream");
FileOutputStream out=mew FileOutputStream(FileDescriptor.out);
System.out.println(new PrintStream(new BufferedOuputStream(out)));
System.out.println("After Re-setting the New Out out stream");
out.close();
//if this is used s.o.flush() should
0
1
2
0
1
2
System.out.flush();
//notwork
}
}
Output:- Before setting the New out stream
After Re-setting the new outstream. If System.out.flush(); is not used, the output will
beonly
one sentence.
In nullcp class:
class nullop extends outputstream
{
public void write(int i)
{
}
}
How the out variable working in the java language at the back:
Out variable of the System class is of type PrintStream. This PrintStream object by
default is connected to the FileDescriptor1(stdout).By default System.in variable will be pointing to FileDescriptor o (stin), System.out will be pointing to FileDescriptor1(stdout) and the System.err will be pointing to the FileDescriptor2 (stderr).But these variables can be programmatically modified by using System.SetIn(), System.setOut and System.setErr().
SequenceInpputStream() SIS:- Provides a convenient mechanism of combining multiple
streams and treating them as a single stream. They can read the File2, when File1 is
completely read and so on.
When we used SIS, the SIS reads the First input Stream and then moves on to the second
input stream. When we execute the available() method on SIS, it simply executes the
available() method on SIS, it simply executes the available() method on the current
inputstream (i.e. from which it is reading).
Example:-
/* Sequence Input Stream Example*/
class iostream2
{
public static void main(String args[])throws Exception
{
byte c1[]={22,23,24,25.......32};
byte c2[]={2,3,4,5,6,7,8,9,0,1,2};
ByteArrayInputStream b1=new ByteArrayInputStream(c1);
ByteArrayInputStream b2=new ByteArrayInputStream(c2));
//SequenceInputStream(InputStream,InputStream);
SequenceInputStream s=new SequenceInpuStream(b1,b2);
for(int i=0;i<15;i++)
{
s.o.p(s.read());
if(i==s)
s.skip(5);
s.o.p("........"+s.available());
}
}
}
Note: we can use all the methods that are used in the ByteArrayInputStream Example.
PipedInput\Output Streams (PIS/POS):- PIS & POS's provides us a mechanism of setting
up a pipe, which allows us to write to POS which can be read from the other end PIS.




P2 requires input from P1. POS is available on PIS.
When we use PIS and POS's, the data from the PIS can be read in the same sequence in
which the data is written by POS.
Ex:- /* piped input/output streams example */
class ioStream6
{
p.s.v.m(String args[])
throws Exception
{
byte c1[]={22,23,24,.........32}
byte c2[]={2,3,4,5,...9};
PipedInputStream pis;
PipedOutputStream pos;
//create an outputstram to which we can write
pos=new PipedOutputStream();
//create an inputstream to read, and connect it to previously created outputstream.
pis=new PipedInputStream(pos);
pos.write(c1,o,c1.length());
s.o.p("data available in pis="+pis.available());
pos.write(c2,o,c2.length());
s.o.p("data available in pis="+pis.available());
pis.read(c1,o,4);
for(int i=0; i<6; i++)
s.o.p(pis.read());
s.o.p("data available in pis="+pis.available());
/* pis.read(c2,o,c2.length());
for(int i=0; i<8; i++)
s.o.p(c2[i]);
s.o.p("data available in pis="+pis.available()); */
}
}
output:-
data available in pis=11
data available in pos=19
25
data available in pis=14
(because 5 bytes are already read by the pis.read(c1,o,4) & s.o.p(pis.read()); reads one)
File Buffers: - these are used to speed up the processing of files/file input & output.

Advgs:-
1. inputstream will be read from the BufferInputStream, but not from the disc to speedup the process. BufferInputStream supports mark() method, so you can use this in your program.
2. output should not be writing to the disc immediately.
3. Most of the people say that BIS/BOS 's are used to increase the performance of an application Since the Buffer is used to temporarily collect the data. But in the case of
FileInput/output Streams , already the o/s provides buffering mechanism in order to
improve the performance of an application.
4.A BufferedInputStream can be used to provide mark operations, For the InputStreams,
which does not directly provide the mark operation.