so I made a program that's basically a simple address book, ( i'm a new programmer). I have it so it reads the contacts from a text file, and saves changes to it too. my issue is it saves just find if I don't add an element to the array before saving ( basically a new contact) but when i do i get "java.lang.NullPointerException at java.io.Writer.write(Unknown Source)" here's my code
package adressbook;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.LineNumberReader;
import java.util.Scanner;
public class marks {
static Scanner scanner = new Scanner(System.in);
// static String studentinfo[][] = { { "", "", "" }, { "", "", "" }, { "", "",
// "" }, { "", "", "" } };
static String studentinfo[][] = new String[4][3];
static int mark[];
static File info = new File("D:\\info.txt");
static int linecount;
static String input;
static int selected;
public static void select() throws IOException {
System.out.println("who would you like to change?");
for (int i = 0; i < studentinfo[0].length; i++) {
System.out.println(i + 1 + "." + studentinfo[0][i]);
}
input = scanner.nextLine();
for (int i = 0; i < studentinfo[0].length; i++) {
// System.out.println(selected);
if (input.equals(studentinfo[0][i])) {
selected = i;
}
}
}
public static void scan() throws IOException {
FileReader input = new FileReader(info);
LineNumberReader count = new LineNumberReader(input);
String lineRead = "";
while ((lineRead = count.readLine()) != null) {
linecount = count.getLineNumber();
}
Scanner s = new Scanner(info);
String[][] resizer = new String[4][linecount / 4];
studentinfo = resizer;
for (int i = 0; i < linecount / 4; i++) {
studentinfo[0][i] = s.nextLine();
System.out.println(studentinfo[0][i]);
studentinfo[1][i] = s.nextLine();
System.out.println(studentinfo[1][i]);
studentinfo[2][i] = s.nextLine();
System.out.println(studentinfo[2][i]);
studentinfo[3][i] = s.nextLine();
System.out.println(studentinfo[3][i]);
}
s.close();
}
public static void printout() {
for (int i = 0; i < studentinfo[0].length; i++) {
System.out.println(studentinfo[0][i]);
System.out.println(studentinfo[1][i]);
System.out.println(studentinfo[2][i]);
System.out.println(studentinfo[3][i]);
}
}
public static void save() throws IOException {
scanner.close();
BufferedWriter writer = new BufferedWriter(new FileWriter(info));
for (int i = 0; i < studentinfo[0].length; i++) {
writer.write(studentinfo[0][i]);
writer.newLine();
writer.write(studentinfo[1][i]);
writer.newLine();
writer.write(studentinfo[2][i]);
writer.newLine();
writer.write(studentinfo[3][i]);
writer.newLine();
}
writer.close();
}
public static void addnew() throws IOException {
System.out.println("enter new name:");
String newname = scanner.next();
System.out.println("enter new number:");
String newnum = scanner.next();
System.out.println("enter new address:");
String newaddr = scanner.next();
System.out.println("enter new email:");
String newemail = scanner.next();
String temp[][] = new String[4][studentinfo.length + 1];
for (int i = 0; i == studentinfo.length; i++) {
temp[0][i] = studentinfo[0][i];
temp[1][i] = studentinfo[1][i];
temp[2][i] = studentinfo[2][i];
temp[3][i] = studentinfo[3][i];
}
studentinfo = temp;
studentinfo[0][studentinfo.length] = newname;
studentinfo[1][studentinfo.length] = newnum;
studentinfo[2][studentinfo.length] = newaddr;
studentinfo[3][studentinfo.length] = newemail;
System.out.println("new contact added!");
save();
// printout();
}
public static void main(String[] args) throws IOException {
scan();// reads in from file
System.out.println("change info? Type yes or no");
input = scanner.nextLine();// gets user input
System.out.println(input);
if (input.equals("yes")) {
select();
System.out.println("name, number, address or email?");
input = scanner.nextLine();
if (input.equals("name")) {
System.out.println("enter new name");
input = scanner.nextLine();
studentinfo[0][selected] = input;
} else if (input.equals("number")) {
System.out.println("enter new number");
input = scanner.nextLine();
studentinfo[1][selected] = input;
} else if (input.equals("address")) {
System.out.println("enter new address");
input = scanner.nextLine();
studentinfo[2][selected] = input;
} else if (input.equals("email")) {
System.out.println("enter new email");
input = scanner.nextLine();
studentinfo[3][selected] = input;
}
printout();
System.out.println("save changes?");
input = scanner.nextLine();
if (input.equals("yes")) {
save();
}
else {
}
}
else if (input.equals("no")) {
System.out.println("add new contact? type yes or no");
input = scanner.next();
if (input.equals("yes")) {
addnew();
}
}
}
}
