Question

Here is my object constructor

static class Edge {
    int source; // source node
    int destination; // destination node
    int weight; // weight of the edge
    int predecessor; // previous node
    public Edge() {};
    public Edge(int s, int d, int w) { source = s; destination = d; weight = w; }
}

Now, here is the statement where I create a new Edge object

edges.add(new Edge(nodeStart, tempDest, tempWeight));

I need to skip over that statement if there has already been an object created with the same parameters (nodeStart, tempDest)

Basically, I don’t want to add the same edge twice.

edges.add(new Edge(0, 1, tempWeight));
edges.add(new Edge(0, 1, tempWeight));

If that happens, I want to make sure it only adds it once, and not new identical objects.

Answer 1

The proper way would be to make edges a Set<Edge>. And then properly override hashcode and equals.

So, you should declare edges like so:

Set<Edge> egdes = new HashSet<Edge>();

And you should implement hashCode and equals like so:

public boolean equals(Object o) {
    if (o == null) return false;
    if (o == this) return true;
    if (!(o instanceof Edge)) return false;
    Edge oEdge = (Edge) o;
    return this.source == oEdge.source && 
           this.destination == oEdge.destination && 
           this.weight == oEdge.weight;
}

public int hashCode(){
    return source * 3 + dest * 11 + weight * 13;
}

You should read up on properly implementing equals and hashCode. My examples are not great. But the general idea is conveyed.