Exception with String array in Java

**sunsolaris2000** · Jul 20 '12, 03:29 PM

I have 3 sql tables: **professors(pr of_id, name)**, **professors_co urses(prof_id, course_id)** and **courses(cours e_id, title)**.

**professors_co urses** is the bridge table between professors and courses.

In *CourseAssignme nts.java* I search which courses belong to professor x, after user enters a professor "name".

**Course.java**

Code:

  public class Course {
        private int course_id;
        private String title;
        
        public Course(int id, String title){
        	super();
        	this.course_id = id;
        	this.title = title;
        }
        
        public int getCourse_id(){
        	return course_id;
        }
        
        public String getTitle(){
        	return title;
        }

Code:

Same with **Professor.java**:

    public class Professor {
       private int prof_id;
       private String name;

............... ....

Code:

Same with **PC.java**:

    public class PC {
      private int prof_id;
      private int course_id;

............... ...

**

Code:

ArrayList<PC> results** contains prof_id <-> course_id

**

Code:

ArrayList<Course> courses** contains course_id <-> title (identical with the table "courses")

I need these for example because let's say:

In "professors " table we have prof_id: 5, name: John;
In "professors_cou rses" we have prof_id: 5, course_id: 1
prof_id: 5, course_id: 9
In "courses" table we have course_id: 1, title: French
course_id: 9, title: Spanish

User enters: "John"

In ArrayList "results" I store:
prof_id: 5, course_id: 1 and prof_id: 5, course_id: 9
So it's similar with the bridge table, but only contains the info regarding "John".

In String cs[] I want to store all the courses of "John", so cs[] = {"French", "Spanish"}

All in all I want to take only the "title" fields from ArrayList "courses" and store them into a String array (cs[]).

In JSP I would display the titles:

Code:

   <%     
        //all the courses that a professor has
        String titles[] = CourseAssignments.getInstance().bridge1("John");
        %>
        
        <html>
           <head></head>
             <body>
             <center>
                <table border="1" cellspacing="1" cellpadding="8" bgcolor= "33FFCC"> 
        			<tr>
        				<td bgcolor= #FF9966><b>Course</b></td>
        			</tr>
        			 	<%
        			    for (int i = 0; i < titles.length; i++){
        			    	if(titles[i] != null){
        				%>
        				<tr>
        				  <td><%= titles[i]%></td>
        				</tr>
        				<%
        	                 }
        	        	}
        %>
        			</table>

I have Exception at the array:

org.apache.jasp er.JasperExcept ion: java.lang.NullP ointerException