java input output

IOSTREAMS

 Stream:--Collection of bits and bytes moving from source to destination and destination to source

These STREAMS are mainly categorized into BYTESTREAM and CHARACTERSTREAMs.

to represent these we have  Pre-defined input and output stream classes in java.io package.

Every java program is connected with mainly 3 stream

ü  System.in-----standard input stream(keyboard)

ü  System.out-----standard output stream(console)

ü  System.err-----standard error stream(console)

 There are different subclasses for InputStream and OutputStream classes.

The FileInputStream and FileOutputSream help reading and writing data from files.  BufferedInputStream and BufferedOutputStream which acts as a cache to perform read/write operations. DataInputStream and DataOutputStream perform read/write operations by taking one byte at a time in primitive data types format.

 The reader and writer classes are used to read/write characters instead of bytes.

Files in Java

File is a collection of records or data. Which can be accessed into a java program by using File class in java.io package.

          File  f1= new File(“temp.txt”);

This is the sytax to declare a file.

Methods of File class 

1.getName() 2.getPath() 3.exists() 4.isFile()/isDirectory()

5.canRead()/canWrite() 6.lastModified() 7.length() 8.delete() 9.renameTo() 10.list() 11.mkdir().

Ex:

import java.io.*;

class Filemethod1{

public static void main(String [] args){

File f1 = new File("c:\\java","abc.txt");

System.out.println("Filename: " + f1.getName());

System.out.println("Filename: " + f1.getPath());

System.out.println("Filename: " + f1.getAbsolutePath());

System.out.println(f1.exists() ? "file exists" : "file not exists");

System.out.println(f1.isDirectory() ? "file is a directory" : "file is  not" + "a directory");

System.out.println(f1.isFile() ? "file is an ordinary file" :"file may be a named pipe");

} }

File Streams

File stream consists of FileInputStream and FileOutputStream.

FileOutputStream: Helps to create a FILE and write data to a file.

FileInputStream: Helps in reading data  from the actual disk files.

import java.io.*;

class IOEx {

      public static void main(String[] args) throws IOException{

                  File f=new File("d:/abc.txt");

                  FileOutputStream  fos=new FileOutputStream(f);

                  fos.write(1);

                 FileInputStream fis=new FileInputStream(f);

                  int x=fis.read();

                  System.out.println("from file"+x);                        

      }

}

//DataInputStream class example

import java.io.*;

class Dis {

   public static void main(String [] args) throws IOException    {

 DataInputStream dis = new DataInputStream(System.in);

System.out.println("enter name");

String name = dis.readLine();

System.out.println("Hello mr " + name);

} }

Ex:

import java.io.*;

public class DataIOStreamDemo {

public static void main(String[] args) {

      try{

      DataOutputStream dos=new DataOutputStream(new FileOutputStream("data.txt"));

      dos.writeChar('A');

      dos.writeBoolean(false);

      dos.writeInt(10);

            dos.writeUTF("hello");//unicode text format

            dos.writeDouble(12.5);

            dos.close();

      FileInputStream fis=new FileInputStream("data.txt");

           DataInputStream dis =new DataInputStream(fis);

         System.out.println("char:" + dis.readChar());

         System.out.println("char:" + dis.readBoolean());

         System.out.println("char:" + dis.readInt());

         System.out.println("char:" + dis.readUTF());

         System.out.println("char:" + dis.readDouble());

           dis.close();

      }catch (Exception e){

                  System.out.println("error:" +e);

      }

}  }

Buffered Reader

    Buffered Reader class is used to read the data in the form of char by char.

//BufferedReader class example

Ex:--

import java.io.*;

public class BreaderIsDemo {

public static void main(String[] args) throws IOException{

String str;

   BufferedReader br = new BufferedReader(new InputStreamReader(System.in));            System.out.println("enter 'exit' to terminate");

      do {

      str=br.readLine();//input

      System.out.println(str);

      }while(!str.equalsIgnoreCase("exit"));

   }  }

Serialization & DeSerialization

Serialization  is a process of converting JAVA objects into NETWORK supported form by storing the OBJECTS into a Serialisable file.

Deserialisation means converting NETWORK supported form to JAVA OBJECTS.

To support the Serialisation process our class must be implemented from java.io.Serializable.

Serialisable is a marker interface(which does’t have any methods) which gives only  identity to its implemented class that, this class is ready for serialization .

if we don’t want to serialize any data we can declare it as “transient”.

Ex:--

import java.io.*;

class Emp implements Serializable{

      int eid;    String ename;

      transient int age;

      Emp(int id,String name,int a){

                  eid=id;

                  ename=name;

                  age=a;

      }

}

class SerializationDeSerialization{

      public static void main(String[] args) throws IOException,Exception{

                  Emp   e1=new   Emp (100,"admin",23);

                  System.out.println(e1.eid +"\t"+e1.ename+"\t"+e1.age);

                  FileOutputStream  fos=new   FileOutputStream("object.ser");

                  ObjectOutputStream  oos=new  ObjectOutputStream(fos);

                  oos.writeObject(e1);

                  System.out.println("object serialized successfully .....");

                  FileInputStream  fis=new       FileInputStream("object.ser");

                  ObjectInputStream  ois=new ObjectInputStream(fis);

                  Emp e=(Emp)ois.readObject();

                  System.out.println("object de-serialized successfully .....");

                  System.out.println(e.eid +"\t"+e.ename+"\t"+e.age);

      }

}                                  

Output:-

100     admin   23

object serialized successfully .....

object de-serialized successfully .....

100     admin   0