Everything works, except my WritetoDisk, it gives me a NullPointerException PLEASE HELP!
/*
* database.java
*
* Created on March 28, 2008 by Karlee
*
* This program allows the user to add/remove students' first & last name, social security number, debt, and GPA
* The user can change te debt and GPA of the students
* The user can scan the list of students by name, debt, or GPA
*
*/
package database;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import javax.swing.JOptionPane;
public class database {
private static ArrayList <String> myList;
public static void main(String[] args) {
//define ArrayList
ArrayList <student> myList = new ArrayList();
//define variables
int choose;
student s;
//menu
do{
choose = Integer.parseInt(JOptionPane.showInputDialog("Choose an option: " +
"\n1) Add a student to the list \n2) Remove a student from the list" +
"\n3) Change the debt & GPA for a student \n4) Scan by last name" +
"\n5) Scan by first name \n6) Scan by debt \n7) Scan by GPA \n8) Print list " +
"\n9) Write to Disk \n10) Exit"));
switch (choose){
//add a new student
case 1: int SSN = Integer.parseInt(JOptionPane.showInputDialog("What is the SSN of the " +
"student you want to add?"));
s = new student("","",SSN,0.0,0.0);
if (myList.indexOf(s)==-1){
s.setFirst(JOptionPane.showInputDialog("What is the first name of the student?"));
s.setLast(JOptionPane.showInputDialog("What is the last name of the student?"));
s.setDebt(Double.parseDouble(JOptionPane.showInputDialog("What is the debt of " +
"the student?")));
s.setGPA(Double.parseDouble(JOptionPane.showInputDialog("What is the GPA of " +
"the student?\nGPA should be on a 4.0 scale")));
myList.add(s);
} else
JOptionPane.showMessageDialog(null, "There is already someone with that " +
"social security number");
break;
//remove a student
case 2: SSN = Integer.parseInt(JOptionPane.showInputDialog("What is the SSN of the " +
"student you want to remove?"));
s = new student("","",SSN,0.0,0.0);
if (myList.indexOf(s)==-1)
JOptionPane.showMessageDialog(null, "Sorry, there is no one in the list with " +
"that social security number");
else{
String decide = JOptionPane.showInputDialog("Are you sure you want to remove " +
"the person with SSN of " + SSN + " ?");
if (decide.equals("yes"))
myList.remove(s);
}
break;
//change the debt & GPA of a student
case 3: SSN = Integer.parseInt(JOptionPane.showInputDialog("What is the SSN of the " +
"student you want to change the debt & GPA of?"));
s = new student("","",SSN,0.0,0.0);
int index=myList.indexOf(s);
if(index>=0){
double debt = Double.parseDouble(JOptionPane.showInputDialog("Change the debt " +
"to: "));
myList.get(index).setDebt(debt);
double gpa = Double.parseDouble(JOptionPane.showInputDialog("Change the GPA " +
"to: "));
myList.get(index).setGPA(gpa);
} else
JOptionPane.showMessageDialog(null, "Sorry, there is no one in the list with " +
"that SSN");
break;
//scan for last name
case 4: String last = JOptionPane.showInputDialog("What is the last name you want to " +
"search for?");
int count=0;
for(int i=0; i<myList.size(); i++){
if(myList.get(i).getLast().equals(last)){
count++;
JOptionPane.showMessageDialog(null, myList.get(i).getFirst() + " " + myList.get(i).getLast());
}
}
if(count==0)
JOptionPane.showMessageDialog(null, "Sorry, there is no one in the list with that " +
"last name");
break;
//scan for first name
case 5: String first = JOptionPane.showInputDialog("What is the first name you want to search " +
"for?");
count=0;
for(int i=0; i<myList.size(); i++)
if(myList.get(i).getFirst().equals(first)){
count++;
JOptionPane.showMessageDialog(null, myList.get(i).getFirst() + " " +
myList.get(i).getLast());
}
if(count==0)
JOptionPane.showMessageDialog(null, "Sorry, there is no one in the list with that " +
"first name");
break;
//scan for debt
case 6: double DEBT = Double.parseDouble(JOptionPane.showInputDialog("What minimum debt do " +
"you want to search for?"));
count=0;
for(int i=0; i<myList.size(); i++)
if(myList.get(i).getDebt()>=(DEBT)){
count++;
JOptionPane.showMessageDialog(null, myList.get(i).getFirst() + " " + myList.get(i).getLast() +
": " + myList.get(i).getDebt());
}
if(count==0)
JOptionPane.showMessageDialog(null, "Sorry, there is no one in the list with that " +
"debt");
break;
//scan for GPA
case 7: double GPAlow = Double.parseDouble(JOptionPane.showInputDialog("What minimum GPA do " +
"you want to search for?" +
"\nGPA should be on a 4.0 scale"));
double GPAhigh = Double.parseDouble(JOptionPane.showInputDialog("What maximum GPA do you " +
"want to search for?\nGPA should be on a 4.0 scale"));
count=0;
for(int i=0; i<myList.size(); i++){
if(myList.get(i).getGPA()>=(GPAlow) && myList.get(i).getGPA()<=(GPAhigh)){
count++;
JOptionPane.showMessageDialog(null, myList.get(i).getFirst() + " " +
myList.get(i).getLast() + ": " + myList.get(i).getGPA());
}
}
if(count==0)
JOptionPane.showMessageDialog(null, "Sorry, there is no one in the list with that " +
"GPA");
break;
//prints the list
case 8: for(int i=0; i<myList.size(); i++)
JOptionPane.showMessageDialog(null, myList.get(i));
break;
//writes the students to a file
case 9: SSN = Integer.parseInt(JOptionPane.showInputDialog("What is the SSN of the" +
" student you want to write to disk?"));
s = new student("","",SSN,0.0,0.0);
try{
WriteToDisk("C:\\Documents and Settings\\Owner\\My Documents\\Karlee\\students.txt");
} catch (IOException ex){
System.out.println("Error Reading from Disk");
}
break;
}
//exits the program
}while(choose !=10);
System.exit(0);
}
//write to file method
public static void WriteToDisk(String Filename) throws IOException{
FileWriter in;
try {
in = new FileWriter( new File(Filename));
}catch (java.io.FileNotFoundException e) {
System.out.println("File: " + Filename + " not found.");
return;
}
//Read the words in one per line
BufferedWriter buffer = new BufferedWriter(in);
for(int i = 0; i < myList.size(); i++) {
buffer.write(myList.get(i));
buffer.newLine();
}
buffer.close();
}
}
