Class Subgraph<V,​E,​G extends Graph<V,​E>>

  • Type Parameters:
    V - the vertex type
    E - the edge type
    G - the type of the base graph
    All Implemented Interfaces:
    java.io.Serializable, Graph<V,​E>
    Direct Known Subclasses:
    DirectedSubgraph, UndirectedSubgraph

    public class Subgraph<V,​E,​G extends Graph<V,​E>>
    extends AbstractGraph<V,​E>
    implements java.io.Serializable
    A subgraph is a graph that has a subset of vertices and a subset of edges with respect to some base graph. More formally, a subgraph G(V,E) that is based on a base graph Gb(Vb,Eb) satisfies the following subgraph property: V is a subset of Vb and E is a subset of Eb. Other than this property, a subgraph is a graph with any respect and fully complies with the Graph interface.

    If the base graph is a ListenableGraph, the subgraph listens on the base graph and guarantees the subgraph property. If an edge or a vertex is removed from the base graph, it is automatically removed from the subgraph. Subgraph listeners are informed on such removal only if it results in a cascaded removal from the subgraph. If the subgraph has been created as an induced subgraph it also keeps track of edges being added to its vertices. If vertices are added to the base graph, the subgraph remains unaffected.

    If the base graph is not a ListenableGraph, then the subgraph property cannot be guaranteed. If edges or vertices are removed from the base graph, they are not removed from the subgraph.

    Modifications to Subgraph are allowed as long as the subgraph property is maintained. Addition of vertices or edges are allowed as long as they also exist in the base graph. Removal of vertices or edges is always allowed. The base graph is never affected by any modification made to the subgraph.

    A subgraph may provide a "live-window" on a base graph, so that changes made to its vertices or edges are immediately reflected in the base graph, and vice versa. For that to happen, vertices and edges added to the subgraph must be identical (that is, reference-equal and not only value-equal) to their respective ones in the base graph. Previous versions of this class enforced such identity, at a severe performance cost. Currently it is no longer enforced. If you want to achieve a "live-window" functionality, your safest tactics would be to NOT override the equals() methods of your vertices and edges. If you use a class that has already overridden the equals() method, such as String, than you can use a wrapper around it, or else use it directly but exercise a great care to avoid having different-but-equal instances in the subgraph and the base graph.

    This graph implementation guarantees deterministic vertex and edge set ordering (via LinkedHashSet).

    Note that this implementation tries to maintain a "live-window" on the base graph, which has implications in the performance of the various operations. For example iterating over the adjacent edges of a vertex takes time proportional to the number of adjacent edges of the vertex in the base graph even if the subgraph contains only a small subset of those edges. Therefore, the user must be aware that using this implementation for certain algorithms might come with computational overhead. For certain algorithms it is better to maintain a subgraph by hand instead of using this implementation as a black box.

    Since:
    Jul 18, 2003
    See Also:
    Graph, Set, Serialized Form
    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      private class  Subgraph.BaseGraphListener
      An internal listener on the base graph.
    • Constructor Summary

      Constructors 
      Constructor Description
      Subgraph​(G base)
      Creates a new induced Subgraph with all vertices included.
      Subgraph​(G base, java.util.Set<? extends V> vertexSubset)
      Creates a new induced Subgraph.
      Subgraph​(G base, java.util.Set<? extends V> vertexSubset, java.util.Set<? extends E> edgeSubset)
      Creates a new Subgraph.
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      E addEdge​(V sourceVertex, V targetVertex)
      Add an edge to the subgraph.
      boolean addEdge​(V sourceVertex, V targetVertex, E e)
      Adds the specified edge to this graph, going from the source vertex to the target vertex.
      boolean addVertex​(V v)
      Adds the specified vertex to this subgraph.
      boolean containsEdge​(E e)
      Returns true if this graph contains the specified edge.
      boolean containsVertex​(V v)
      Returns true if this graph contains the specified vertex.
      java.util.Set<E> edgeSet()
      Returns a set of the edges contained in this graph.
      java.util.Set<E> edgesOf​(V vertex)
      Returns a set of all edges touching the specified vertex.
      java.util.Set<E> getAllEdges​(V sourceVertex, V targetVertex)
      Returns a set of all edges connecting source vertex to target vertex if such vertices exist in this graph.
      G getBase()
      Get the base graph.
      E getEdge​(V sourceVertex, V targetVertex)
      Returns an edge connecting source vertex to target vertex if such vertices and such edge exist in this graph.
      EdgeFactory<V,​E> getEdgeFactory()
      Returns the edge factory using which this graph creates new edges.
      V getEdgeSource​(E e)
      Returns the source vertex of an edge.
      V getEdgeTarget​(E e)
      Returns the target vertex of an edge.
      double getEdgeWeight​(E e)
      Returns the weight assigned to a given edge.
      private void initialize​(java.util.Set<? extends V> vertexFilter, java.util.Set<? extends E> edgeFilter)  
      boolean removeEdge​(E e)
      Removes the specified edge from the graph.
      E removeEdge​(V sourceVertex, V targetVertex)
      Removes an edge going from source vertex to target vertex, if such vertices and such edge exist in this graph.
      boolean removeVertex​(V v)
      Removes the specified vertex from this graph including all its touching edges if present.
      void setEdgeWeight​(E e, double weight)
      Assigns a weight to an edge.
      java.util.Set<V> vertexSet()
      Returns a set of the vertices contained in this graph.
      • Methods inherited from class java.lang.Object

        clone, finalize, getClass, notify, notifyAll, wait, wait, wait
    • Field Detail

      • NO_SUCH_EDGE_IN_BASE

        private static final java.lang.String NO_SUCH_EDGE_IN_BASE
        See Also:
        Constant Field Values
      • NO_SUCH_VERTEX_IN_BASE

        private static final java.lang.String NO_SUCH_VERTEX_IN_BASE
        See Also:
        Constant Field Values
      • edgeSet

        protected final java.util.Set<E> edgeSet
      • vertexSet

        protected final java.util.Set<V> vertexSet
      • base

        protected final G extends Graph<V,​E> base
      • isInduced

        protected final boolean isInduced
      • unmodifiableEdgeSet

        private transient java.util.Set<E> unmodifiableEdgeSet
      • unmodifiableVertexSet

        private transient java.util.Set<V> unmodifiableVertexSet
    • Constructor Detail

      • Subgraph

        public Subgraph​(G base,
                        java.util.Set<? extends V> vertexSubset,
                        java.util.Set<? extends E> edgeSubset)
        Creates a new Subgraph.
        Parameters:
        base - the base (backing) graph on which the subgraph will be based.
        vertexSubset - vertices to include in the subgraph. If null then all vertices are included.
        edgeSubset - edges to in include in the subgraph. If null then all the edges whose vertices found in the graph are included.
      • Subgraph

        public Subgraph​(G base,
                        java.util.Set<? extends V> vertexSubset)
        Creates a new induced Subgraph. The subgraph will keep track of edges being added to its vertex subset as well as deletion of edges and vertices. If base it not listenable, this is identical to the call Subgraph(base, vertexSubset, null).
        Parameters:
        base - the base (backing) graph on which the subgraph will be based.
        vertexSubset - vertices to include in the subgraph. If null then all vertices are included.
      • Subgraph

        public Subgraph​(G base)
        Creates a new induced Subgraph with all vertices included. The subgraph will keep track of edges being added to its vertex subset as well as deletion of edges and vertices. If base it not listenable, this is identical to the call Subgraph(base, null, null).
        Parameters:
        base - the base (backing) graph on which the subgraph will be based.
    • Method Detail

      • getAllEdges

        public java.util.Set<E> getAllEdges​(V sourceVertex,
                                            V targetVertex)
        Returns a set of all edges connecting source vertex to target vertex if such vertices exist in this graph. If any of the vertices does not exist or is null, returns null. If both vertices exist but no edges found, returns an empty set.

        In undirected graphs, some of the returned edges may have their source and target vertices in the opposite order. In simple graphs the returned set is either singleton set or empty set.

        Specified by:
        getAllEdges in interface Graph<V,​E>
        Parameters:
        sourceVertex - source vertex of the edge.
        targetVertex - target vertex of the edge.
        Returns:
        a set of all edges connecting source vertex to target vertex.
      • getEdge

        public E getEdge​(V sourceVertex,
                         V targetVertex)
        Returns an edge connecting source vertex to target vertex if such vertices and such edge exist in this graph. Otherwise returns null. If any of the specified vertices is null returns null

        In undirected graphs, the returned edge may have its source and target vertices in the opposite order.

        Specified by:
        getEdge in interface Graph<V,​E>
        Parameters:
        sourceVertex - source vertex of the edge.
        targetVertex - target vertex of the edge.
        Returns:
        an edge connecting source vertex to target vertex.
      • getEdgeFactory

        public EdgeFactory<V,​E> getEdgeFactory()
        Returns the edge factory using which this graph creates new edges. The edge factory is defined when the graph is constructed and must not be modified.
        Specified by:
        getEdgeFactory in interface Graph<V,​E>
        Returns:
        the edge factory using which this graph creates new edges.
      • addEdge

        public E addEdge​(V sourceVertex,
                         V targetVertex)
        Add an edge to the subgraph. The end-points must exist in the subgraph and the edge must exist in the base graph. In case multiple such edges exist in the base graph, one that is not already in the subgraph is chosen arbitrarily and added to the subgraph. In case all such edges already exist in the subgraph, the method returns null.
        Specified by:
        addEdge in interface Graph<V,​E>
        Parameters:
        sourceVertex - the source vertex
        targetVertex - the source vertex
        Returns:
        the added edge or null if all such edges from the base graph already belong in the subgraph
        Throws:
        java.lang.IllegalArgumentException - if the source or target vertex does not belong to the subgraph
        java.lang.IllegalArgumentException - if the base graph does not contain any edge between the two end-points
        See Also:
        Graph.getEdgeFactory()
      • addEdge

        public boolean addEdge​(V sourceVertex,
                               V targetVertex,
                               E e)
        Adds the specified edge to this graph, going from the source vertex to the target vertex. More formally, adds the specified edge, e, to this graph if this graph contains no edge e2 such that e2.equals(e). If this graph already contains such an edge, the call leaves this graph unchanged and returns false. Some graphs do not allow edge-multiplicity. In such cases, if the graph already contains an edge from the specified source to the specified target, than this method does not change the graph and returns false. If the edge was added to the graph, returns true.

        The source and target vertices must already be contained in this graph. If they are not found in graph IllegalArgumentException is thrown.

        Specified by:
        addEdge in interface Graph<V,​E>
        Parameters:
        sourceVertex - source vertex of the edge.
        targetVertex - target vertex of the edge.
        e - edge to be added to this graph.
        Returns:
        true if this graph did not already contain the specified edge.
        See Also:
        Graph.addEdge(Object, Object), Graph.getEdgeFactory()
      • addVertex

        public boolean addVertex​(V v)
        Adds the specified vertex to this subgraph.
        Specified by:
        addVertex in interface Graph<V,​E>
        Parameters:
        v - the vertex to be added.
        Returns:
        true if the vertex was added, otherwise false.
        Throws:
        java.lang.NullPointerException - if v is null
        java.lang.IllegalArgumentException - if the base graph does not contain the vertex
        See Also:
        Subgraph, Graph.addVertex(Object)
      • containsEdge

        public boolean containsEdge​(E e)
        Returns true if this graph contains the specified edge. More formally, returns true if and only if this graph contains an edge e2 such that e.equals(e2). If the specified edge is null returns false.
        Specified by:
        containsEdge in interface Graph<V,​E>
        Parameters:
        e - edge whose presence in this graph is to be tested.
        Returns:
        true if this graph contains the specified edge.
      • containsVertex

        public boolean containsVertex​(V v)
        Returns true if this graph contains the specified vertex. More formally, returns true if and only if this graph contains a vertex u such that u.equals(v). If the specified vertex is null returns false.
        Specified by:
        containsVertex in interface Graph<V,​E>
        Parameters:
        v - vertex whose presence in this graph is to be tested.
        Returns:
        true if this graph contains the specified vertex.
      • edgeSet

        public java.util.Set<E> edgeSet()
        Returns a set of the edges contained in this graph. The set is backed by the graph, so changes to the graph are reflected in the set. If the graph is modified while an iteration over the set is in progress, the results of the iteration are undefined.

        The graph implementation may maintain a particular set ordering (e.g. via LinkedHashSet) for deterministic iteration, but this is not required. It is the responsibility of callers who rely on this behavior to only use graph implementations which support it.

        Specified by:
        edgeSet in interface Graph<V,​E>
        Returns:
        a set of the edges contained in this graph.
      • edgesOf

        public java.util.Set<E> edgesOf​(V vertex)
        Returns a set of all edges touching the specified vertex. If no edges are touching the specified vertex returns an empty set.
        Specified by:
        edgesOf in interface Graph<V,​E>
        Parameters:
        vertex - the vertex for which a set of touching edges is to be returned.
        Returns:
        a set of all edges touching the specified vertex.
      • removeEdge

        public boolean removeEdge​(E e)
        Removes the specified edge from the graph. Removes the specified edge from this graph if it is present. More formally, removes an edge e2 such that e2.equals(e), if the graph contains such edge. Returns true if the graph contained the specified edge. (The graph will not contain the specified edge once the call returns).

        If the specified edge is null returns false.

        Specified by:
        removeEdge in interface Graph<V,​E>
        Parameters:
        e - edge to be removed from this graph, if present.
        Returns:
        true if and only if the graph contained the specified edge.
      • removeEdge

        public E removeEdge​(V sourceVertex,
                            V targetVertex)
        Removes an edge going from source vertex to target vertex, if such vertices and such edge exist in this graph. Returns the edge if removed or null otherwise.
        Specified by:
        removeEdge in interface Graph<V,​E>
        Parameters:
        sourceVertex - source vertex of the edge.
        targetVertex - target vertex of the edge.
        Returns:
        The removed edge, or null if no edge removed.
      • removeVertex

        public boolean removeVertex​(V v)
        Removes the specified vertex from this graph including all its touching edges if present. More formally, if the graph contains a vertex u such that u.equals(v), the call removes all edges that touch u and then removes u itself. If no such u is found, the call leaves the graph unchanged. Returns true if the graph contained the specified vertex. (The graph will not contain the specified vertex once the call returns).

        If the specified vertex is null returns false.

        Specified by:
        removeVertex in interface Graph<V,​E>
        Parameters:
        v - vertex to be removed from this graph, if present.
        Returns:
        true if the graph contained the specified vertex; false otherwise.
      • vertexSet

        public java.util.Set<V> vertexSet()
        Returns a set of the vertices contained in this graph. The set is backed by the graph, so changes to the graph are reflected in the set. If the graph is modified while an iteration over the set is in progress, the results of the iteration are undefined.

        The graph implementation may maintain a particular set ordering (e.g. via LinkedHashSet) for deterministic iteration, but this is not required. It is the responsibility of callers who rely on this behavior to only use graph implementations which support it.

        Specified by:
        vertexSet in interface Graph<V,​E>
        Returns:
        a set view of the vertices contained in this graph.
      • getEdgeSource

        public V getEdgeSource​(E e)
        Returns the source vertex of an edge. For an undirected graph, source and target are distinguishable designations (but without any mathematical meaning).
        Specified by:
        getEdgeSource in interface Graph<V,​E>
        Parameters:
        e - edge of interest
        Returns:
        source vertex
      • getEdgeTarget

        public V getEdgeTarget​(E e)
        Returns the target vertex of an edge. For an undirected graph, source and target are distinguishable designations (but without any mathematical meaning).
        Specified by:
        getEdgeTarget in interface Graph<V,​E>
        Parameters:
        e - edge of interest
        Returns:
        target vertex
      • getBase

        public G getBase()
        Get the base graph.
        Returns:
        the base graph
      • getEdgeWeight

        public double getEdgeWeight​(E e)
        Returns the weight assigned to a given edge. Unweighted graphs return 1.0 (as defined by WeightedGraph.DEFAULT_EDGE_WEIGHT), allowing weighted-graph algorithms to apply to them where meaningful.
        Specified by:
        getEdgeWeight in interface Graph<V,​E>
        Parameters:
        e - edge of interest
        Returns:
        edge weight
        See Also:
        WeightedGraph
      • setEdgeWeight

        public void setEdgeWeight​(E e,
                                  double weight)
        Assigns a weight to an edge.
        Parameters:
        e - edge on which to set weight
        weight - new weight for edge
        See Also:
        WeightedGraph.setEdgeWeight(Object, double)
      • initialize

        private void initialize​(java.util.Set<? extends V> vertexFilter,
                                java.util.Set<? extends E> edgeFilter)