Question

in java

Write a contacts database program that presents the user with a menu that allows the user to select between the following options:

• Save a contact.
• Search for a contact.
• Print all contacts out to the screen.
• Quit

If the user selects the first option, the user is prompted to enter a person's name and phone number which will get saved at the end of a file named contacts.txt.
If the user selects the second option, the program prompts the user asking for the name of the contact. It then searches the contacts.txt for a matching name. If found, it displays the phone number on the screen. If not found, it will display an appropriate error message.
If the user selects the third option, the program displays all contacts stored in contacts.txt in a neat table.
The program is menu driven and will repeat presenting the menu and processing choices until the user selects the fourth option to quit.
If the user selects an invalid option, an appropriate error message should be displayed.
If the user selects to print all contacts to the screen with no stored contacts, an appropriate error message should be displayed.

You may use message dialogs or make it a purely console-based application

Answer 1

///////////////////ContactsProgram.java//////////////////////////////////

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;

public class ContactsProgram {
   private static final String FILE_NAME="contacts.txt";//filename is taken as a constant
  
   //scanner and FileWriter instance variable declared
   private static Scanner sc = null;
   private static FileWriter fw = null;
  
   //main method
   public static void main(String[] args){
       File file = new File(FILE_NAME);
       try {
           file.createNewFile();
       } catch (IOException e) {
           System.out.println("Error:"+e.getMessage());
       }//A new file is created in the classpath
      
       do{
           int choice = printMenu();
          
           //menu logic based on user choice
           if(choice ==1){ //if 1: save contact
               saveContact(file);
           }else if(choice ==2){ //if 2: search contact
               searchContact(file);
           }else if(choice ==3){ //if 3: display all contacts
               printAllContacts(file);
           }else if(choice ==4){//if 4: exit after closing scanner
               System.out.println("Thank you!");
               sc.close();
               break;
           }else{//other choice: show error
               System.out.println("Error: Invalid choice!");
           }
          
       }while(true);//loop indefinitely until user choose 4
      
   }
  
   /**
   * get the menu choice from user
   * @return
   */
   public static int printMenu(){
       sc = new Scanner(System.in);
       System.out.println("1. Save a contact.");
       System.out.println("2. Search for a contact.");
       System.out.println("3. Print all contacts out to the screen.");
       System.out.println("4. Quit.");
      
       System.out.println("Enter your choice:");
       int choice = Integer.parseInt(sc.nextLine());
       return choice;
   }
  
   /**
   * Take data from user and store contact in the next available line in contacts file
   * @param file
   */
   public static void saveContact(File file){
       sc = new Scanner(System.in);
       System.out.println("Enter person's name:");
       String name = sc.nextLine();
       System.out.println("Enter person's phone number:");
       String phoneNumber = sc.nextLine();
       try {
           fw = new FileWriter(file,true); //open the file in append mode to write
           fw.append(name +","+phoneNumber+"\n");//append the line
           fw.close();//close the fw
       } catch (IOException e) {
           System.out.println("Error in writing into file!");
       }
      
   }
  
   /**
   * search contact's phone number from file if the entered name is found
   * if name is not found then error message will be displayed.
   * @param file
   */
   public static void searchContact(File file){
       sc = new Scanner(System.in);
       System.out.println("Enter persons name to search:");
       String name = sc.nextLine();
       String phoneNumber = null;
       try {
           sc = new Scanner(file);
       } catch (FileNotFoundException e) {
           System.out.println("file not found!");
           return;
       }
       while(sc.hasNextLine()){
           String currentLine = sc.nextLine();
           String[] data = currentLine.split(",");
           if(data[0].equals(name)){
               phoneNumber = data[1];
               break;
           }
       }
       if(phoneNumber!=null){
           System.out.println("Phone number for "+name + " is : "+phoneNumber);
       }else{
           System.out.println("Tha name "+name+" is NOT FOUND in the contacts file!");
       }
      
   }
  
   //print all contacts form file in console
   public static void printAllContacts(File file){
       try{      
           sc = new Scanner(file);
       }catch(FileNotFoundException fe){
           System.out.println("File Not Found!");
           return;
       }
       int counter = 0;
       while(sc.hasNextLine()){
           counter++;
           if(counter ==1){
               System.out.println(String.format("%-20s\t%-20s", "Name","PhoneNumber"));
               System.out.println("----------------------------------------------------------");
           }
           String currentLine = sc.nextLine();
           String[] data = currentLine.split(",");
           String name = data[0];
           String phoneNumber = data[1];
           System.out.println(String.format("%-20s\t%-20s", name,phoneNumber));
       }
      
       if(counter==0){//if there is no entry in the file
           System.out.println("Error:There is no contacts to be displayed!");
       }
   }

}

==================================

OUTPUT

==================================

1. Save a contact.
2. Search for a contact.
3. Print all contacts out to the screen.
4. Quit.
Enter your choice:
1
Enter person's name:
tomas
Enter person's phone number:
5675675432
1. Save a contact.
2. Search for a contact.
3. Print all contacts out to the screen.
4. Quit.
Enter your choice:
1
Enter person's name:
samuel
Enter person's phone number:
3344556677
1. Save a contact.
2. Search for a contact.
3. Print all contacts out to the screen.
4. Quit.
Enter your choice:
1
Enter person's name:
ian
Enter person's phone number:
8765432100
1. Save a contact.
2. Search for a contact.
3. Print all contacts out to the screen.
4. Quit.
Enter your choice:
1
Enter person's name:
jacky
Enter person's phone number:
6758760987
1. Save a contact.
2. Search for a contact.
3. Print all contacts out to the screen.
4. Quit.
Enter your choice:
3
Name     PhoneNumber   
----------------------------------------------------------
tomas    5675675432
samuel     3344556677
ian    8765432100
jacky    6758760987
1. Save a contact.
2. Search for a contact.
3. Print all contacts out to the screen.
4. Quit.
Enter your choice:
2
Enter persons name to search:
samuel
Phone number for samuel is : 3344556677
1. Save a contact.
2. Search for a contact.
3. Print all contacts out to the screen.
4. Quit.
Enter your choice:
2
Enter persons name to search:
nil
Tha name nil is NOT FOUND in the contacts file!
1. Save a contact.
2. Search for a contact.
3. Print all contacts out to the screen.
4. Quit.
Enter your choice:
1
Enter person's name:
nil
Enter person's phone number:
0157896321
1. Save a contact.
2. Search for a contact.
3. Print all contacts out to the screen.
4. Quit.
Enter your choice:
3
Name     PhoneNumber   
----------------------------------------------------------
tomas    5675675432
samuel     3344556677
ian    8765432100
jacky    6758760987
nil    0157896321
1. Save a contact.
2. Search for a contact.
3. Print all contacts out to the screen.
4. Quit.
Enter your choice:
2
Enter persons name to search:
nil
Phone number for nil is : 0157896321
1. Save a contact.
2. Search for a contact.
3. Print all contacts out to the screen.
4. Quit.
Enter your choice:
4
Thank you!

======================================

The file: contacts.txt(that has been generated

======================================