/*
 * Copyright (C) 2016 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.graph;

import static com.google.common.graph.GraphConstants.MULTIPLE_EDGES_CONNECTING;
import static java.util.Collections.unmodifiableSet;

import com.google.common.annotations.Beta;
import com.google.common.base.Function;
import com.google.common.base.Predicate;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterators;
import com.google.common.collect.Maps;
import com.google.common.collect.Sets;
import com.google.common.math.IntMath;
import java.util.AbstractSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import org.checkerframework.checker.nullness.qual.Nullable;

This class provides a skeletal implementation of Network. It is recommended to extend this class rather than implement Network directly.

The methods implemented in this class should not be overridden unless the subclass admits a more efficient implementation.

Author:James Sexton
Type parameters:
  • <N> – Node parameter type
  • <E> – Edge parameter type
Since:20.0
/** * This class provides a skeletal implementation of {@link Network}. It is recommended to extend * this class rather than implement {@link Network} directly. * * <p>The methods implemented in this class should not be overridden unless the subclass admits a * more efficient implementation. * * @author James Sexton * @param <N> Node parameter type * @param <E> Edge parameter type * @since 20.0 */
@Beta public abstract class AbstractNetwork<N, E> implements Network<N, E> { @Override public Graph<N> asGraph() { return new AbstractGraph<N>() { @Override public Set<N> nodes() { return AbstractNetwork.this.nodes(); } @Override public Set<EndpointPair<N>> edges() { if (allowsParallelEdges()) { return super.edges(); // Defer to AbstractGraph implementation. } // Optimized implementation assumes no parallel edges (1:1 edge to EndpointPair mapping). return new AbstractSet<EndpointPair<N>>() { @Override public Iterator<EndpointPair<N>> iterator() { return Iterators.transform( AbstractNetwork.this.edges().iterator(), new Function<E, EndpointPair<N>>() { @Override public EndpointPair<N> apply(E edge) { return incidentNodes(edge); } }); } @Override public int size() { return AbstractNetwork.this.edges().size(); } // Mostly safe: We check contains(u) before calling successors(u), so we perform unsafe // operations only in weird cases like checking for an EndpointPair<ArrayList> in a // Network<LinkedList>. @SuppressWarnings("unchecked") @Override public boolean contains(@Nullable Object obj) { if (!(obj instanceof EndpointPair)) { return false; } EndpointPair<?> endpointPair = (EndpointPair<?>) obj; return isDirected() == endpointPair.isOrdered() && nodes().contains(endpointPair.nodeU()) && successors((N) endpointPair.nodeU()).contains(endpointPair.nodeV()); } }; } @Override public ElementOrder<N> nodeOrder() { return AbstractNetwork.this.nodeOrder(); } @Override public boolean isDirected() { return AbstractNetwork.this.isDirected(); } @Override public boolean allowsSelfLoops() { return AbstractNetwork.this.allowsSelfLoops(); } @Override public Set<N> adjacentNodes(N node) { return AbstractNetwork.this.adjacentNodes(node); } @Override public Set<N> predecessors(N node) { return AbstractNetwork.this.predecessors(node); } @Override public Set<N> successors(N node) { return AbstractNetwork.this.successors(node); } // DO NOT override the AbstractGraph *degree() implementations. }; } @Override public int degree(N node) { if (isDirected()) { return IntMath.saturatedAdd(inEdges(node).size(), outEdges(node).size()); } else { return IntMath.saturatedAdd(incidentEdges(node).size(), edgesConnecting(node, node).size()); } } @Override public int inDegree(N node) { return isDirected() ? inEdges(node).size() : degree(node); } @Override public int outDegree(N node) { return isDirected() ? outEdges(node).size() : degree(node); } @Override public Set<E> adjacentEdges(E edge) { EndpointPair<N> endpointPair = incidentNodes(edge); // Verifies that edge is in this network. Set<E> endpointPairIncidentEdges = Sets.union(incidentEdges(endpointPair.nodeU()), incidentEdges(endpointPair.nodeV())); return Sets.difference(endpointPairIncidentEdges, ImmutableSet.of(edge)); } @Override public Set<E> edgesConnecting(N nodeU, N nodeV) { Set<E> outEdgesU = outEdges(nodeU); Set<E> inEdgesV = inEdges(nodeV); return outEdgesU.size() <= inEdgesV.size() ? unmodifiableSet(Sets.filter(outEdgesU, connectedPredicate(nodeU, nodeV))) : unmodifiableSet(Sets.filter(inEdgesV, connectedPredicate(nodeV, nodeU))); } private Predicate<E> connectedPredicate(final N nodePresent, final N nodeToCheck) { return new Predicate<E>() { @Override public boolean apply(E edge) { return incidentNodes(edge).adjacentNode(nodePresent).equals(nodeToCheck); } }; } @Override public Optional<E> edgeConnecting(N nodeU, N nodeV) { Set<E> edgesConnecting = edgesConnecting(nodeU, nodeV); switch (edgesConnecting.size()) { case 0: return Optional.empty(); case 1: return Optional.of(edgesConnecting.iterator().next()); default: throw new IllegalArgumentException(String.format(MULTIPLE_EDGES_CONNECTING, nodeU, nodeV)); } } @Override public @Nullable E edgeConnectingOrNull(N nodeU, N nodeV) { return edgeConnecting(nodeU, nodeV).orElse(null); } @Override public boolean hasEdgeConnecting(N nodeU, N nodeV) { return !edgesConnecting(nodeU, nodeV).isEmpty(); } @Override public final boolean equals(@Nullable Object obj) { if (obj == this) { return true; } if (!(obj instanceof Network)) { return false; } Network<?, ?> other = (Network<?, ?>) obj; return isDirected() == other.isDirected() && nodes().equals(other.nodes()) && edgeIncidentNodesMap(this).equals(edgeIncidentNodesMap(other)); } @Override public final int hashCode() { return edgeIncidentNodesMap(this).hashCode(); }
Returns a string representation of this network.
/** Returns a string representation of this network. */
@Override public String toString() { return "isDirected: " + isDirected() + ", allowsParallelEdges: " + allowsParallelEdges() + ", allowsSelfLoops: " + allowsSelfLoops() + ", nodes: " + nodes() + ", edges: " + edgeIncidentNodesMap(this); } private static <N, E> Map<E, EndpointPair<N>> edgeIncidentNodesMap(final Network<N, E> network) { Function<E, EndpointPair<N>> edgeToIncidentNodesFn = new Function<E, EndpointPair<N>>() { @Override public EndpointPair<N> apply(E edge) { return network.incidentNodes(edge); } }; return Maps.asMap(network.edges(), edgeToIncidentNodesFn); } }