title: NullPointerException When Entering Data Into a Dynamic Array from Text File
body: <p>I am making a voting system where the user logs in with their student number and makes a selection. Once someone has voted, they cannot be able to log in again. I made an object; Students, containing a String for the student number and a boolean for whether or not that student number has already voted (both being private). I made a dynamic array of this type as to accept a given amount of students off of a text file that is read through the use of a Scanner. However, when I try to populate the student number string within the object array, I get a NullPointerException. The Scanner IS reading the information from the text file, but the error occurs when I try to put the information into the private string of the Student object. When I use an array of strings everything works fine, but then I don't have the boolean to tell whether or not someone has already voted. I am quite new to programming and have no idea what the problem is. Can someone please explain what is wrong and how it can be fixed?</p>
  
  <p>Method where text file is read and array is populated(students is declared and constructed globally, initially having the size of 0):</p>
  
  <pre><code>public static void getStudentNumbers(){
  
    int a = 0;
    while(fileReader.hasNext()){
  
      if (a &gt;= students.length) 
      {
        int newSize = 1 + students.length; 
        Student[] newData = new Student[newSize];         
        System.arraycopy(students, 0, newData, 0, students.length);         
        students = newData;       
      }
      students[a].setStudentNumber(fileReader.nextLine()); //Error occurs here
      a++;
   }
  }
  </code></pre>
  
  <p>Student Object:</p>
  
  <pre><code>public class Student{
    private Boolean hasVoted = false;
    private String studentNumber = "";
  
    public void setVotedStatus(Boolean voted){
      hasVoted = voted;
    }
  
    public void setStudentNumber(String studentNum){
      studentNumber = studentNum; 
    }
  
    public Boolean getVotedStatus(){
      return hasVoted;
    }
  
    public String getStudentNumber(){
      return studentNumber;
    } 
  }
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>java.lang.NullPointerException
   at VotingSystem2_0.getStudentNumbers(VotingSystem2_0.java:279)
   at VotingSystem2_0.main(VotingSystem2_0.java:245)
   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
   at java.lang.reflect.Method.invoke(Unknown Source)
   at edu.rice.cs.drjava.model.compiler.JavacCompiler.runCommand(JavacCompiler.java:272) 
  </code></pre>
  
  <p>Thanks in advance!</p>