// Simple encapsulation in Java with simple terminal I/O

import java.io.*;

class Student
{
  private String ssn;
  private String name;
  private int age;
  public String get_ssn () { return ssn; }
  public String get_name () { return name; }
  public long get_age () { return age; }
  public void set_ssn (String new_ssn) 
  { 
      ssn = new String(new_ssn);
  }    
  public void set_name (String new_name)
  {
    name = new String(new_name);
  }
  public void set_age (int new_age)
  {
    if (new_age > 0 && new_age <= 110)
      age = new_age;
    else
      System.err.println("Age is not legal");
  }
  // Provide a constructor for Student for proper initialization
  Student (String sn, String s, int y)
  {
    set_ssn(sn);
    set_name(s);
    set_age(y);
  }
  // display function
  public void display ()
  {
    System.err.println("Data for Student with Ssn: " + ssn);
    System.err.println("\tName: " + name + " Age: " + age);
  }
}

class Database
{
  private Student Students[];
  Database (int max) { Students = new Student[max]; }
  private int num_Students = 0;
  // function to locate a Student on the list; return -1 if not there
  public int find_Student (String sn)
  {
    for (int i = 0; i < num_Students; i++)
      // note the comparison below does NOT use ==
      if ((Students[i].get_ssn()).equals(sn))
	return i;
    return -1;
  }

  // function to add a new Student to the list; if duplicate (sn)
  // reject with an error message
  public void add_Student (Student x)
  {
    if (num_Students == Students.length)
      {
	System.err.println("Error -- database is full");
	return;
      }
    int there = find_Student(x.get_ssn());
    if (there != -1) 
      {
	System.err.println("Error -- that ssn number exists already");
	return;
      }
    Students[num_Students] = x;
    num_Students = num_Students + 1;
  }

  // function to remove a Student;  use list compaction if you wish
  // error message if sn is not on the list
  public void remove_Student (String sn)
  {
    int there = find_Student(sn);
    if (there == -1)
      {
	System.err.println("Cannot delete -- not on the list");
	return;
      }
    // compaction of remaining elements...
    for (int i=there+1; i < num_Students; i++)
      Students[i-1] = Students[i];
    num_Students = num_Students - 1;
  }

  // function to display a Student if it is on the list
  public void display_Student (String sn)
  {
    int there = find_Student(sn);
    if (there == -1)
      {
	System.err.println("Cannot display -- not on the list");
	return;
      }
    Students[there].display();
  }
  public void display_all()
  {
    for (int i = 0; i < num_Students; i++)
      Students[i].display();
  }
}

class StudentDB
{

  public static void main (String args[]) throws IOException
  {
    Database D1 = new Database(100);
    String m, inputstring;
    String sn;
    int y;

    String com;
    //DataInputStream ds = new DataInputStream(System.in);

    BufferedReader din = new BufferedReader(new InputStreamReader(System.in));

    System.out.print("Enter command: ");
    com = din.readLine().trim();
    while (! com.equalsIgnoreCase("QUIT"))
      {
	if (com.equalsIgnoreCase("ADD"))
	  {
	    System.out.print("Enter ssn: ");
	    sn = din.readLine();
	    System.out.print("Enter name: ");
	    m = din.readLine();
	    System.out.print("Enter age: ");
	    inputstring = din.readLine();
	    y = Integer.parseInt(inputstring);
	    D1.add_Student(new Student(sn, m, y));
	  }
	else if (com.equalsIgnoreCase( "REMOVE"))
	  {
	    System.out.print("Enter ssn: ");
	    sn = din.readLine();
	    D1.remove_Student(sn);
	  }

	else if (com.equalsIgnoreCase("DISPLAY"))
	  {
	    System.out.print("Enter ssn: ");
	    sn = din.readLine();
	    D1.display_Student(sn);
	  }

	else if (com.equalsIgnoreCase("SHOWALL"))
	  {
	    D1.display_all();
	  }

	else
	  System.out.println("Error case");

	System.out.print("Enter next command: ");
	com = din.readLine();
	
      }
  }
}