error

[Victoria Preston]

I am trying to run my program....but everytime I do I get an error message that says
Exception in thread "main" java.lang.NullPointerException

what does this mean

[Ernest Friedman-Hill]

It means that something on the left side of a dot (.) is 'null' -- either a variable is set to null, or a function is returning null. The stack trace (the error message) tells you what line the error happened at: the top line will say something like

at MyClass.main (MyClass.java:21)

that means the error happened on line 21 of MyClass.java . Look at any dots on that line -- that's where the problem is. We'd be happy to look at the code for you, if you want -- paste it into a reply in this thread. Put [ CODE ] [/ CODE ] tags around the code to preserve formatting in your post (take out the spaces in the tags.)

[Victoria Preston]

public boolean contains(int id)
{
  boolean result;
  result = false;
  for(int i=0; i<list.length; i++)
  {
   if(list[i].equals(id))
   {
    result = true;
   }
   else
   {
   result= false;
   }
  }
return result;
}

there is the code i'm trying to test and here is the code in my test

public static void main(String[] args)
{
  EmployeeList list = new EmployeeList();
  Employee emp1 = new Employee("Smith, Jay B", "Oak St");
  Employee emp2 = new Employee("Jones, Ann E", "Elm St");
if( list.contains(2))System.out.println("ID #2 is there.");
else System.out.println("ID #2 is not there.");
if( list.contains(emp2))System.out.println("Ann Jones is there.");
else System.out.println("Ann Jones is not there.");
}

hope you can help

[Ernest Friedman-Hill]

You didn't show the stack trace or tell me what line it says the error is on, so I have to guess!

The method "contains" references a member variable named "list" (different from the local variable in main of the same name). The member variable "list" is an array. My first guess is that either that member variable is "null" (does anything ever assign a value to it?) or one of the elements of that array is "null" (remember that constructing an array makes an array of null references; there are no objects in the array until they are created.

But it looks like "contains" is as method in some kind of a collection class; it's likely that there's a separate variable that tells how many elements are really in the array; this number is smaller than or equal to the size of the array. The member variable that hold this count should be used as the upper limit of the for loop, not the array length.

Do any of these hints help?

[Victoria Preston]

so instead of .length it needs to be .size


and yes they help bunches thanks

[Ernest Friedman-Hill]

Originally posted by Victoria Preston:
so instead of .length it needs to be .size

Well, no, not exactly. I'm imagining that EmployeeClass looks like

class EmployeeClass {
  private String[] list;
  private int size;
  // ... more
 
  public boolean contains() // ...  
}

So I'm talking about using "size" in place of "list.length" -- but this is only if my guess is right that there is a member like "size". Maybe you should show us the whole "EmployeeList" class (unless you figure this out by yourself now.)

[Victoria Preston]

okay sorry about the hold up had to go to the store. Here is the entire EmployeeList any feedback would help.

public class EmployeeList
{
private Employee[] list;
private int numEmployees;
private final int DEFAULT_INITAL_CAPACITY = 2;
private int capacity;
private int size;
private int employeeID;

public EmployeeList()
{
numEmployees = 0;
list = new Employee[DEFAULT_INITAL_CAPACITY];
   }

public EmployeeList(int cap)
{
cap = capacity;
if(cap<=0)
  cap = DEFAULT_INITAL_CAPACITY;
}

public void add(Employee anEmployee)
{

for(int i=0; i<list.length; i++)
{
if(this.equals(anEmployee))

list[i]= new Employee();
}

}

public Employee remove(Employee anEmployee)
{
for(int i=0; i<list.length; i++)
{
if(list[i].equals(anEmployee))
numEmployees--;
}
return null;
}

public Employee remove(int id)
{
id = employeeID;
for(int i=0; i<list.length; i++)
{
if(this.equals(id))
numEmployees = numEmployees-1;
}
return null;

}

public Employee get(int id)
{
employeeID = id;
for(int i=0; i<list.length; i++)
{
if(list[i].equals(id))
list[i].getEmployeeName();
}
return null;

}

public void clear()
{
}

public boolean contains(int id)
{
boolean result;
result = false;
for(int i=0; i<list.length; i++)
{
if(list[i].equals(id))
{
result = true;
}
else
{
result= false;
}
}
return result;
}

public boolean contains(Employee anEmployee)
{
boolean result;
result = false;

for(int i=0; i<list.length; i++)
{
if(list[i].equals(anEmployee))
{
result = true;
}
else
{
result= false;
}
}
return result;
}

public boolean isEmpty()
{
boolean result;
result = false;

for(int i=0; i<list.length; i++)
{
if(size ==0)
{
result = true;
}
else
{
result = false;
}
}
return result;
}

public int getCapacity()
{
return capacity;
}

public int size()
{
return list.length;
}

public Employee[] toArray()
{
return list;
}

public String toString()
{
String message = "EMPLOYEE LIST" + '\n' + list;
return message;
}
}