Data Streams and Object Streams in Java

[Bigga Lexx]

Hello Friends,
I have done some basic coding in Java programming language. I know that a Java program uses a stream to either read data items from a source or to write data items to a destination. But in streams I am not able to get the data and object streams. So thought that posting here would be helpful. Please tell me what are the Data Streams and Object Streams in Java.? Waiting for your replies..!!

[MELTRONICS]

Data Streams and Object Streams are the types of the I/O Streams. An I/O Stream represents an input source or an output destination. Many different kinds of sources like disk files, devices, memory arrays, etc. are represented by a stream. Data Streams support binary I/O of primitive data type values and String values. In the data type value can contain boolean, char, byte, short, int, long, float, and double. Object streams support I/O of objects just like data streams support I/O of primitive data types. Java divides streams into input and output categories. Java also divides streams into byte-oriented and character-oriented categories. Hope that you got the basics about the data streams and object streams.

[Deabelos]

Java's class library includes many stream classes. A problem with the FileInputStream and FileOutputStream classes is that they only work at the byte level. You can use the DataInputStream and DataOutputStream classes for reading integers, writing floating-point values, etc. The above mentioned classes are located in the java.io package portion of Java's standard class library. The data stream classes are designed so that their objects can be chained to other streams. All data streams implement either the DataInput interface or the DataOutput interface. The object stream classes are ObjectInputStream and ObjectOutputStream. These classes implement ObjectInput and ObjectOutput.

[void]

I have tried to explain the coding in program of the Data Streams. The following program defines some constants containing the name of the data file :

static final String dataFile = "dataexample";

static final double[] prices = { 17.99, 11.99, 12.99, 7.99, 6.99 };
static final int[] units = { 14, 7, 16, 22, 44 };
static final String[] descs = { "Java Band",
        "Java Glass",
        "Duke Juggling Dolls",
        "Java Stapler",
        "Java Locket" };
// Then DataStreams opens an output stream.

out = new DataOutputStream(new
            BufferedOutputStream(new FileOutputStream(dataFile)));
// DataStreams writes out the records and closes the output stream. 

for (int i = 0; i < prices.length; i ++) {
    out.writeDouble(prices[i]);
    out.writeInt(units[i]);
    out.writeUTF(descs[i]);
}

[CodGuru]

I have used the DataOutputStream and DataInputStream to write and read non-byte-oriented data items in my code. Hope that you will get some idea from the below coding :

import java.io.*;

class IODemo
{
  public static void main (String [] args)
  {
   DataOutputStream dstream = null;

   try
   {
     FileOutputStream fos = new FileOutputStream ("example.dat");
     dstream = new DataOutputStream (fos);

     dstream.writeInt (256);
     dstream.writeDouble (Math.PI);
     dstream.writeUTF ("Java");

   }
   catch (IOException e)
   {
     System.out.println (e.getMessage ());
     return;
   }
   finally
   {
     if (dstream != null)
       try
       {
         dstream.close ();
       }
       catch (IOException e)
       {
       }
   }

   DataInputStream dis = null;

   try
   {
     FileInputStream fis = new FileInputStream ("example.dat");
     dis = new DataInputStream (fis);

     System.out.println (dis.readInt ());
     System.out.println (dis.readDouble ());
     System.out.println (dis.readUTF ());
   }
   catch (IOException e)
   {
     System.out.println (e.getMessage ());
     return;
   }
   finally
   {
     if (dis != null)
       try
       {
         dis.close ();
       }
       catch (IOException e)
       {
       }
   }
  }
}

[MindSpace]

In many cases you have to write an object to a stream twice, you're really writing only the reference twice. Just glace the following code :

Object obj = new Object();
out.writeObject(obj);
out.writeObject(obj);

If you want to match each writeObject by a readObjec, then the code that reads the stream back will look something like this :

Object obj1 = in.readObject();
Object obj2 = in.readObject();