// File: IO21.java (Module 13)
//
// Author: Rahul Simha
// Created: Nov 28, 1998
//
// Reading and writing raw data - random access.

import java.io.*;

class Person {
    String name;
    int age;

    public Person (String name, int age)
    {
	this.age = age;
	if (name.length() > 5)
	    this.name = name.substring (0,5);
	else {
	    this.name = name;
	    for (int i=name.length()+1; i<=5; i++)
		this.name = this.name + " ";
	}
    }

    public String toString ()
    {
	return "Person: name=" + name + ", age=" + age;
    }

}

public class IO21 {

    public static void main (String[] argv)
    {
	try {
	    File f = new File ("Persons.data");
	    int len = (int) f.length();
	    int recordSize = len / 3;
	    System.out.println ("Record size = " + recordSize);

	    // Let's get the second record.
	    FileInputStream fis = new FileInputStream (f);
	    DataInputStream dis = new DataInputStream (fis);
	    dis.skipBytes (recordSize);

	    char[] nameArray = new char[5];
	    for (int i=0; i<5; i++)
		nameArray[i] = dis.readChar();
	    String name = new String (nameArray);
	    int age = dis.readInt();
	    System.out.println ("Read: name=" + name + ", age=" + age);

	    dis.close();

	    // Using a RandomAccessFile
	    RandomAccessFile raf = new RandomAccessFile (f, "rw");
	    raf.seek (recordSize);
	    nameArray = new char[5];
	    for (int i=0; i<5; i++)
		nameArray[i] = raf.readChar();
	    name = new String (nameArray);
	    age = raf.readInt();
	    System.out.println ("Read: name=" + name + ", age=" + age);

	    // Writing.
	    raf.seek (2*recordSize);
	    Person p = new Person ("ddd", 24);
	    raf.writeChars (p.name);
	    raf.writeInt (p.age);

	    // Read again.
	    raf.seek (2*recordSize);
	    nameArray = new char[5];
	    for (int i=0; i<5; i++)
		nameArray[i] = raf.readChar();
	    name = new String (nameArray);
	    age = raf.readInt();
	    System.out.println ("Read: name=" + name + ", age=" + age);
	    raf.close();
	}
	catch (IOException e) { System.out.println (e); }
    }

}