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POJava contact list program using singleton pattern
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copied!<p>I have to made a simple program which acts as a contact list. The program has main functionality such as: adding new contact, deleting contact, view all contact and save contacts to a file. The main problem for me is that the program must use singleton pattern. I have never used it before. So just wrote it normal how I can. Can anyone help me to make it as singleton?</p> <pre><code>class Contact{ private String name; private String address; private String email; private String phone; Contact(String name, String address, String email, String phone){ this.name=name; this.address=address; this.email=email; this.phone=phone; } public Contact() { } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getPhone() { return phone; } public void setPhone(String phone) { this.phone = phone; } @Override public String toString() { return "Contact{" + "name=" + name + ", address=" + address + ", email=" + email + ", phone=" + phone + '}'; } public int compareTo(Contact c){ return name.compareTo(c.getName()); } public void write(){ try{ Contact contact; contact = new Contact(); Contact c = contact; File file = new File("ContactList.txt"); if(!file.exists()){ file.createNewFile(); try(PrintWriter writer = new PrintWriter(new FileWriter("ContactList.txt", true))){ writer.printf("%s\r\n", name + ", " + address + ", " + email + ", " + phone); writer.flush(); writer.close(); }catch(Exception e){ e.printStackTrace(); } } }catch(Exception e){ e.printStackTrace(); } } public class ContactList { ArrayList<Contact> contactlist = new ArrayList<Contact>(); Contact contact; private int top = 0; public static void main(String[] args){ Contact contact; contact = new Contact(); Contact c = contact; ContactList list = new ContactList(); BufferedReader keyIn = new BufferedReader(new InputStreamReader(System.in)); String choose = ""; while(true){ System.out.println("\n[1] Add contact"); System.out.println("[2] Delete contact"); System.out.println("[3] View all contacts"); System.out.println("[4] Edit contact"); System.out.println("[5] Exit"); System.out.print("Choose : "); try{ choose = keyIn.readLine(); }catch(Exception e){ System.out.println("Error"); } if(choose.equals("1")) { list.addContact(); }else if(choose.equals("2")) { list.deleteContact(); }else if(choose.equals("3")) { list.viewContacts(); }else if(choose.equals("4")) { list.editContact(); }else if(choose.equals("5")) { System.exit(0); }else { System.out.println ("Error"); } } } public void addContact(){ BufferedReader keyIn = new BufferedReader(new InputStreamReader(System.in)); String name = ""; String address = ""; String email = ""; String phone = ""; try{ System.out.print("Name: "); name = keyIn.readLine(); System.out.print("Address "); address = keyIn.readLine(); System.out.print("E-mail address: "); email = keyIn.readLine(); System.out.print("Phone number: "); phone = keyIn.readLine(); }catch(Exception e){ e.printStackTrace(); } Contact contact = new Contact(name, address, email, phone); contactlist.add(contact); top++; try{ contact.write(); }catch(Exception e){ e.printStackTrace(); } } public void deleteContact(){ BufferedReader keyIn = new BufferedReader(new InputStreamReader(System.in)); int index = 0; if(top == 0){ System.out.println("Empty contact lis"); } try{ viewContacts(); System.out.println("\nChoose number to delete: "); index = Integer.parseInt(keyIn.readLine())-1; }catch(Exception e){ e.printStackTrace(); } if(index < 0 || index >= top){ System.out.println("No contact match"); }else{ contactlist.remove(contact); top--; } try{ contact.write(); }catch(Exception e){ e.printStackTrace(); } } public void viewContacts(){ for(int index = 0; index < top; index++){ System.out.println((index+1)+ " Name " + contactlist.get(index).getName()); System.out.println("Address: " + contactlist.get(index).getAddress()); System.out.println("E-mail: " + contactlist.get(index).getEmail()); System.out.println("Phone: " + contactlist.get(index).getPhone()); } } public void editContact(){ BufferedReader keyIn = new BufferedReader(new InputStreamReader(System.in)); int index = 0; String name = ""; String address = ""; String email = ""; String phone = ""; try{ System.out.print("Edit contact: "); index = Integer.parseInt(keyIn.readLine())-1; System.out.print("Name: "); name = keyIn.readLine(); System.out.print("Address: "); address = keyIn.readLine(); System.out.print("E-mail: "); email = keyIn.readLine(); System.out.print("Phone: "); phone = keyIn.readLine(); }catch(Exception e){ e.printStackTrace(); } Contact contact = new Contact(name, address, email, phone); contactlist.add(index, contact); try{ contact.write(); }catch(Exception e){ e.printStackTrace(); } } </code></pre> <p>}</p>

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