Scala example source code file (bug592.scala)

This example Scala source code file (bug592.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

concretedirectedgraph, directedgraph, edge, edge, edgeimpl, edgeimpl, graph, list, list, nil, node, node, nodeimpl, nodeintf

The Scala bug592.scala source code

trait Graph {
  type Edge;
  type Node <: NodeIntf;

  trait NodeIntf {
    def connectWith(node: Node): Edge;
  }

  def nodes: List[Node];
  def edges: List[Edge];
  def addNode: Node;

  protected var ids = 0;
}

abstract class DirectedGraph extends Graph {
  type Edge <: EdgeImpl;

  class EdgeImpl(origin: Node, dest: Node) {
    def from = origin;
    def to = dest;
    override def toString = ""+origin+" --> "+dest
  }

  class NodeImpl extends NodeIntf { self: Node =>
    val id = ids
    ids = ids + 1
    def connectWith(node: Node): Edge = {
      val edge = newEdge(this, node);
      edges = edge :: edges;
      edge;
    }
    override def toString = "Node "+id
  }

  protected def newNode: Node;
  protected def newEdge(from: Node, to: Node): Edge;
  var nodes: List[Node] = Nil;
  var edges: List[Edge] = Nil;

  def addNode: Node = {
    val node = newNode;
    nodes = node :: nodes;
    node;
  }
}

class ConcreteDirectedGraph extends DirectedGraph {
  type Edge = EdgeImpl;
  type Node = NodeImpl;

  protected def newNode: Node = {
    new NodeImpl;
  }

  protected def newEdge(f: Node, t: Node): Edge = {
    new EdgeImpl(f, t);
  }
}

object ExplicitThis {
  def main(args: Array[String]): Unit = {
    val g: Graph = new ConcreteDirectedGraph;
    val n1 = g.addNode;
    val n2 = g.addNode;
    val n3 = g.addNode;
    Console.println(n1.connectWith(n2))
    Console.println(n2.connectWith(n3))
    Console.println(n1.connectWith(n3))
  }
}