Class Edge

1
2	/*
3	* Copyright (c) 2016 Vivid Solutions.
4	*
5	* All rights reserved. This program and the accompanying materials
6	* are made available under the terms of the Eclipse Public License 2.0
7	* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
8	* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
9	* and the Eclipse Distribution License is available at
10	*
11	* http://www.eclipse.org/org/documents/edl-v10.php.
12	*/
13	package org.locationtech.jts.planargraph;
14
15	/**
16	* Represents an undirected edge of a {@link PlanarGraph}. An undirected edge
17	* in fact simply acts as a central point of reference for two opposite
18	* {@link DirectedEdge}s.
19	* <p>
20	* Usually a client using a <code>PlanarGraph</code> will subclass <code>Edge</code>
21	* to add its own application-specific data and methods.
22	*
23	* @version 1.7
24	*/
25	public class Edge
26	extends GraphComponent
27	{
28
29	/**
30	* The two DirectedEdges associated with this Edge.
31	* Index 0 is forward, 1 is reverse.
32	*/
33	protected DirectedEdge[] dirEdge;
34
35	/**
36	* Constructs an Edge whose DirectedEdges are not yet set. Be sure to call
37	* {@link #setDirectedEdges(DirectedEdge, DirectedEdge)}
38	*/
39	public Edge()
40	{
41	}
42
43	/**
44	* Constructs an Edge initialized with the given DirectedEdges, and for each
45	* DirectedEdge: sets the Edge, sets the symmetric DirectedEdge, and adds
46	* this Edge to its from-Node.
47	*/
48	public Edge(DirectedEdge de0, DirectedEdge de1)
49	{
50	setDirectedEdges(de0, de1);
51	}
52
53	/**
54	* Initializes this Edge's two DirectedEdges, and for each DirectedEdge: sets the
55	* Edge, sets the symmetric DirectedEdge, and adds this Edge to its from-Node.
56	*/
57	public void setDirectedEdges(DirectedEdge de0, DirectedEdge de1)
58	{
59	dirEdge = new DirectedEdge[] { de0, de1 };
60	de0.setEdge(this);
61	de1.setEdge(this);
62	de0.setSym(de1);
63	de1.setSym(de0);
64	de0.getFromNode().addOutEdge(de0);
65	de1.getFromNode().addOutEdge(de1);
66	}
67
68	/**
69	* Returns one of the DirectedEdges associated with this Edge.
70	* @param i 0 or 1. 0 returns the forward directed edge, 1 returns the reverse
71	*/
72	public DirectedEdge getDirEdge(int i)
73	{
74	return dirEdge[i];
75	}
76
77	/**
78	* Returns the {@link DirectedEdge} that starts from the given node, or null if the
79	* node is not one of the two nodes associated with this Edge.
80	*/
81	public DirectedEdge getDirEdge(Node fromNode)
82	{
83	if (dirEdge[0].getFromNode() == fromNode) return dirEdge[0];
84	if (dirEdge[1].getFromNode() == fromNode) return dirEdge[1];
85	// node not found
86	// possibly should throw an exception here?
87	return null;
88	}
89
90	/**
91	* If <code>node</code> is one of the two nodes associated with this Edge,
92	* returns the other node; otherwise returns null.
93	*/
94	public Node getOppositeNode(Node node)
95	{
96	if (dirEdge[0].getFromNode() == node) return dirEdge[0].getToNode();
97	if (dirEdge[1].getFromNode() == node) return dirEdge[1].getToNode();
98	// node not found
99	// possibly should throw an exception here?
100	return null;
101	}
102
103	/**
104	* Removes this edge from its containing graph.
105	*/
106	void remove() {
107	this.dirEdge = null;
108	}
109
110	/**
111	* Tests whether this edge has been removed from its containing graph
112	*
113	* @return <code>true</code> if this edge is removed
114	*/
115	public boolean isRemoved()
116	{
117	return dirEdge == null;
118	}
119
120	}
121