Cannot reference this before supertype constructor has been called

Question

I'm confused. I would like it easier for a user to use a class where one item can be determined from another, but I'm having a problem with the constructors.
First, one constructor that works fine:
    public UndirectedGraph(List nodes, List edges) {
        this(nodes, edges, 100, 100, true, false);
    }which then calls the ultimate constructor that accepts all those other parameters.
The problem is with this one:
    public UndirectedGraph(List nodes) {
        this(nodes, collectEdges(nodes), 100, 100, true, false);
    }collectEdges returns a List of Edges, so technically all should be fine. However, this won't compile, with the message:
UndirectedGraph.java [37:1] cannot reference this before supertype constructor has been called
        this(nodes, collectEdges(nodes));
                           ^
1 error
Errors compiling UndirectedGraph.Is there a workaround for what I'm trying to do? It'd be a lot easier to have this collectEdges() method in this single place than in any class that's using this one.

Answer 1

You HAVE to call the super constructor before you do anything else in the constructor. You can make calls to this but the final constructor to be executed has to make the super call. I am assuming you are subclassing something here because this should not show up as an error if there is a default constuctor. The reson for this is that a subclass is built on top of its parent classes meaning it can access information in them methods in them etc. Even in the constrcutor it can do this so the super class MUST be created before the subclass.