TreeSet only adding 1 element....

[asiavoices]

Hello all,

I have a strange situation where when I try to add an object to a TreeSet collection, its only adding the first (1st) one and ignores the rest. There were no errors, etc. when compiling.

The funny thing is that when I use ArrayList, its okay (but not sorted as expected).


Here's part of my code:


public class MyApp
{
private TreeSet mylist;

public MyApp()
{
......
}


public static void main(String[] args)
{
MyApp myapp = new MyApp();
myapp.test();
}


public void test()
{
// Create my stuff objects
doStuff();
System.out.println("\n"
}

public void doStuff()
{
mylist = new TreeSet();

// add 1st element

Car c1 = new Car();
try
{
c1.setCode("12345678"
}
catch (Exception e){
System.out.println(e.toString());
}
try
{
c1.setName("Chrysler"
}
catch (Exception e)
{
System.out.println(e.toString());
}


// add 2nd element

Car c2 = new Car();
try
{
c2.setCode("fg1951235"
}
catch (Exception e){
System.out.println(e.toString());
}
try
{
c2.setName("Ford"
}
catch (Exception e)
{
System.out.println(e.toString());
}

// add 3rd element

Car c3 = new Car();
try
{
c3.setCode("2458878921"
}
catch (Exception e){
System.out.println(e.toString());
}
try
{
c3.setName("BMW"
}
catch (Exception e)
{
System.out.println(e.toString());
}


mylist.add(c1);
mylist.add(c2);
mylist.add(c3);

System.out.println("\nNo. of elements: " + mylist.size());

System.out.println("\nContents in the SortedSet: " + mylist);

Iterator thelist = mylist.iterator();
while (mylist.hasNext())
{
Car currentcar = (Car) thelist.next();
System.out.println("Car code:" + currentcar.getCode() + "\nName: " + currentcar.getName().trim());
}

} // end of MyApp



Results displayed: ==================

No. of elements: 1

Contents in the SortedSet: [null] <-- this is weird should be something like [Car@12453] or similar.

Car code: 12345678
Name: Chrysler


Any ideas why this may be happening?

Cheers,

Christopher

 

[idarke]

TreeSet will eliminate duplicate objects. Try overriding the &quot;equals&quot; method in your Car class to provide a way of telling one from another based on the Car Code.

 

[asiavoices]

Thanks idarke,

That's interesting because they are not duplicate (as far as the code and name data is concerned).

Can you suggest how I do an equal test?

Thanks,

Christopher

 

[idarke]

I don't really understand how java determines the &quot;natural order&quot; of objects. I assume it's comparing based on the output from the toString() method.

Another thing to try is to implement the Comparable interface on your Car class and write a compareTo method. This will allow you to directly control the sort order. My understanding is that the compareTo method should consider the same things as &quot;equal&quot; that the equals method does.

Hope this helps...

 

[asiavoices]

Thank you.

I was able to get it to work now. I forgot that when I implemented the comparable interface, I did not code in the compareTo() method.

cheers,

Christopher