I/O

Class DataOutputStream

• It is usedto write primitive type of values to an output stream.

• DataOutputStream(OutputStream out)
  • Creates a new data output stream to write data to the specified underlying output stream.

• void writeInt(int v)
• Writes an int to the underlying output stream as four bytes.
• void writeLong(long v)
• Writes a long to the underlying output stream as eight bytes.
• void writeFloat(float v)
• void writeDouble(double v)
• void writeChar(int v)
• Writes a char to the underlying output stream as a 2-byte value.
• void writeChars(String s)
• Writes a string to the underlying output stream as a sequence of characters.

 import java.io.*;
 class demo
 {
    public static void main(String args[])throws Exception
	  {
	    int arr[]={134654665,284976359,375696944,478499493,588388383,
        698876566,764545453,855454545,978656544,107474733};
      FileOutputStream fout=new FileOutputStream("c:/temp/num.txt");
	    DataOutputStream ds=new DataOutputStream(fout);
	    for(int i=0;i<arr.length;i++)
		    ds.writeInt(arr[i]);
	    ds.close();
	    fout.close();
	    System.out.println("values stored...");
	  }
 }

  values stored...

Class DataInputStream

• It is used to read primitive types of values from an underlying input stream.

• DataInputStream(InputStream in)
  • Creates a DataInputStream that uses the specified underlying InputStream.

• int readInt()
• read an int value from Stream.
• long readLong()
• read an long value from Stream.
• char readChar()
• read an char value from Stream.
• float readFloat()
• read an float value from Stream.
• double readDouble()
• read an double value from Stream.

 import java.io.*;
 class demo
 {
    public static void main(String args[])throws Exception
	  {
	    FileInputStream fin=new FileInputStream("c:/temp/num.txt");
	    DataInputStream ds=new DataInputStream(fin);
	    for(int i=1;i<=10;i++)
		  {
		    int n=ds.readInt();
		    System.out.println(n);
		  }
	    ds.close();
	    fin.close();
	  }
 }

134654665 
284976359 
375696944 
478499493 
588388383 
698876566 
764545453 
855454545 
978656544 
107474733

Class RandomAccessFile

• This class support both reading and writing to a random access file.
• It contains a file pointer which indicates a point at which read or write operation is to be performed.

• RandomAccessFile(File file, String mode)
• RandomAccessFile(String name, String mode)
• It opens the specified file in specified mode.
• Mode can be r, w, rw, a ...etc

• void writeByte(int v)
• void writeBytes(String s)
• void writeInt(int v)
• void writeLong(long v)
• void writeFloat(float v)
• void writeDouble(double v)
• Will write different types of values to file
• byte readByte()
• int readInt()
• long readLong()
• float readFloat()
• double readDouble()
• Will read different type of values from a file
• long getFilePointer()
• This method returns the current offset in this file.
• void seek(long pos)
• This method sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs.
• int skipBytes(int n)
• This method attempts to skip over n bytes of input discarding the skipped bytes.

 import java.io.*;
 class demo
 {
    public static void main(String args[])throws Exception
	  {
	    RandomAccessFile rd=new RandomAccessFile("c:/temp/num.txt","r");
	    rd.skipBytes(4);
	    int a=rd.readInt();
	    rd.skipBytes(8);
	    int b=rd.readInt();
	    rd.seek(32);
	    int c=rd.readInt();
	    rd.close();
	    System.out.println("Values are "+a+" "+b+" "+c);
	  }
 }

Values are 284976359 588388383 978656544