السلام .. كيف أسوي تعديل للبيانات (update) +شرح

ممكن التعديل على ال case 5 وإذا ممكن شرح معنى كل كود

import java.io.*;
import java.util.*;

public class test {

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

Scanner input = new Scanner(System.in);


//...........................................................................
   	boolean quit = false;
 do { 
            int menu = 0;
          System.out.println("******************************");
     	System.out.println("Telephone Directory");
     	System.out.println();
     	System.out.println("1. Accept Data");
     	System.out.println("2. Search");
     	System.out.println("3. List of all persons");
     	System.out.println("4. Exit");
     	System.out.println("5. update");


     	System.out.print("Please enter your choice: ");
     	menu = input.nextInt();
     	System.out.println();
//...........................................................................
 switch (menu) {
 case 1:
          System.out.print("Enter Name: ");
          String name = input.next();
          System.out.print("Enter Address: ");
          String address = input.next();
          System.out.print("Enter Phone No: ");
          int no = input.nextInt();
          FileWriter fw = new FileWriter(new File("directory.txt"), true);
          BufferedWriter out = new BufferedWriter(fw);
          out.write(name + " " + address + " " + no);
          out.write(name + " " + address + " " + no);
          out.newLine();
          out.close();
     	System.out.println( name + " " + address + " " + no);

    break;
//...........................................................................
   	case 2://Search
            System.out.print("Enter name to search information: ");
     	String n = input.next();
     	File f = new File("directory.txt");
 	try {
          BufferedReader freader = new BufferedReader(new FileReader(f));
          String s;
          while ((s = freader.readLine()) != null) {
          String[] st = s.split(" ");
          String nm = st[0];
          String add = st[1];
          String phoneNo = st[2];
          if (n.equals(nm)) {
          System.out.println("***********Information**************");
          System.out.println("Address : " + add);
          System.out.println("PhoneNo : " + phoneNo);
     	}
     	}
     	freader.close();
     	} 
    catch (Exception e) {
                            }
        break;
//...........................................................................   
   case 3://list
      FileInputStream fis = new FileInputStream(new File("directory.txt"));

 	try {
 		DataInputStream dis = new DataInputStream(fis);
 	BufferedReader reader = new BufferedReader( new InputStreamReader(dis));
 	String st;
   ArrayList al = new ArrayList();
   while ((st = reader.readLine()) != null) {
      al.add(st);
 	}
 	Iterator itr;
 	for (itr = al.iterator(); itr.hasNext()[img=/public/style_emoticons/default/wink_smile.gif] {
 	String str = itr.next().toString();
 	String[] splitSt = str.split(" ");
 	String na = "", ada = "", ph = "";
 	for (int i = 0; i < splitSt.length; i++) {
 	na = splitSt[0];
 	ada = splitSt[1];
 	ph = splitSt[2];
                                   	}
    System.out.println(na + " " + ada + " " + ph);
      }

     	reader.close();
     	} 
    catch (Exception e) {
                            }

   	break;
//...........................................................................
   case 4 ://exit
          quit = true;
   break;
//...........................................................................
  case 5 ://update 
       System.out.print("Enter name to update information: ");
     	String a = input.next();
     	File fi = new File("directory.txt");
 	try {        //  }
          }
     	freader1.close();
     	} 
    catch (Exception e) {
                            }
  break;
   default:
        System.out.println("Invalid Entry!");
        }
        } while (!quit);
}
}

test.java