This program is a small contact manager. I am having a problem calling the sortContacts method. It gives me a nullpointerexception every time I call the method. I am trying to have the method sort the contacts from A-Z but for some reason the arrays appear to be empty? The text file they are loaded from in loadContacts has entries in it, and prints perfectly fine (with the index number) when displayContacts is called.
I have tried using ArrayLists to no avail. It just seems like comparing strings inside arrays will just never work?
Exception in thread "main" java.lang.NullPointerException
at Contacts.sortContacts(Contacts.java:179)
at Contacts.menu(Contacts.java:47)
at Contacts.main(Contacts.java:25)
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
public class Contacts {
//global variables
public static int counter = 0;
static BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
static int x;
static String[] name = new String[101];
static String[] number = new String[101];
public static void main(String[] args) throws IOException {//main method, sends user to the menu method
menu();
}
//The menu method displays the option menu and compares user input to a menu option
public static void menu() throws IOException{
int choice = -1;
while (choice != 7){
System.out.println("Main Menu");
System.out.println("1. View all Contacts\n2. Add Entry\n3. Modify Entry\n4. Delete Entry\n5. Save\n6. Load\n7. Sort Conacts\n8. Exit");
choice = Integer.valueOf(in.readLine()).intValue();
switch(choice){
case 1: displayContacts();
break;
case 2: addContact();
break;
case 3: modifyContact();
break;
case 4: deleteContact();
break;
case 5: saveContact();
break;
case 6: loadContact();
break;
case 7: sortContacts(name);
break;
default:System.exit(0);//terminates the program (quit)
}
}
}
private static void displayContacts() throws IOException {
System.out.println(counter);
for(int i = 0; i < counter; i++){
if(name != null) {//this loops prevents the program from printing out empty contact slots
System.out.println("Contact " + i + ": " + name[i] + " | " + number[i]);
}
else{
System.out.print("");
}
}
}
public static void addContact() throws IOException {
//check the counter variable
int print;
BufferedReader scan = new BufferedReader(new FileReader("contacts.txt"));
print = Integer.valueOf(scan.readLine()).intValue();
print = counter;
if (counter < 101){
//prompt the user for information
System.out.println("Enter the Contact's name:");
name[counter] = in.readLine();
System.out.println("Enter the Contact's number");
number[counter] = in.readLine();
//increment the counter
counter++;
} else {
System.out.println("Sorry the array is full!");
}
scan.close();
}
public static void modifyContact() throws IOException{
boolean found = false;
int flag = 0;
String modCon;
System.out.println("Enter the name of the contact you wish to modify:");
modCon = in.readLine();
for (int i = 0; i < counter; i++){
if (modCon.compareTo(name[i]) == 0){
flag = i;
found = true;
}
}
if (found == false){
System.out.println("Item not found");
}
else{
System.out.println("Contact found!");
System.out.println("Enter new name: ");
name[flag] = in.readLine();
System.out.println("Enter new number: ");
number[flag] = in.readLine();
}
}
private static void deleteContact() throws IOException {
boolean found = false;
int flag = -1;
String delCon;
System.out.println("Enter the name of the contact you wish to delete:");
delCon = in.readLine();
for(int i = 0; i < counter; i++){
if(delCon.compareTo(name[i]) == 0) {
flag = i;
found = true;
}
}
if(found == false){
System.out.println("Item not found");
}
else{
if (flag == counter - 1){
name[flag] = "";
number[flag] = "";
counter--;
} else{
for (int i = flag; i < counter; i++){
name[i] = name[i + 1];
number[i] = number[i + 1];
}
}
}
counter = flag + 1;
}
public static void saveContact() throws IOException{
//Create File output
PrintWriter output;
output = new PrintWriter(new FileWriter("contacts.txt"));
//Output a header to the file, in this case it is the number of criminals
output.println(counter);
//loop through our array outputting to a file
for(int i = 0; i < counter; i++){
System.out.println("Writing Contact to file");
output.println(name[i]);
output.println(number[i]);
}
output.close();
}
public static void loadContact() throws IOException {
int print;
BufferedReader in = new BufferedReader(new FileReader("contacts.txt"));
print = Integer.valueOf(in.readLine()).intValue();
counter = print; // tells the counter where to continue from (if loading a file)
System.out.println("Loading " + print + " Contacts");
for (int i = 0; i < print; i++){
//read in the data
name[i] = in.readLine();
number[i] = in.readLine();
}
in.close();
}
public static void sortContacts(String[] a) throws IOException{
//counters i and j
int i = 0;
int j = 0;
//"smallest" flag"
int smallest = 0;
//temporary holder for swapping
String temp;
//Selection Sort
for (i = 0; i < 100; i++){
smallest = i;
for (j = i; j < 10; j++){
//compare the current smallest with the current array element
if (name[j].compareTo(name[smallest]) < 0){
smallest = j;
}
//swap the smallest
temp = name[i];
name[i] = name[smallest];
name[smallest] = temp;
}
}
}
}
