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Java example source code file (DirectedNodeAdjacencies.java)

This example Java source code file (DirectedNodeAdjacencies.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

abstractiterator, abstractset, adjacency, annotation, both, directednodeadjacencies, entry, expected_degree, iterator, map, override, pred, safe, set, suppresswarnings, util

The DirectedNodeAdjacencies.java Java example source code

/*
 * 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.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.graph.GraphConstants.EXPECTED_DEGREE;

import com.google.common.collect.AbstractIterator;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;

import java.util.AbstractSet;
import java.util.Collections;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import javax.annotation.Nullable;

/**
 * A class representing an origin node's adjacent nodes in a directed graph.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 */
final class DirectedNodeAdjacencies<N> implements NodeAdjacencies {
  enum Adjacency {
    PRED,
    SUCC,
    BOTH;
  }

  private final Map<N, Adjacency> adjacentNodes;

  private int predecessorCount;
  private int successorCount;

  private DirectedNodeAdjacencies(
      Map<N, Adjacency> adjacentNodes, int predecessorCount, int successorCount) {
    this.adjacentNodes = checkNotNull(adjacentNodes, "adjacentNodes");
    this.predecessorCount = predecessorCount;
    this.successorCount = successorCount;
  }

  static <N> DirectedNodeAdjacencies of() {
    // We store predecessors and successors in the same map, so expected size is twice the degree.
    int inAndOutDegree = EXPECTED_DEGREE * 2;
    return new DirectedNodeAdjacencies<N>(
        Maps.<N, Adjacency>newHashMapWithExpectedSize(inAndOutDegree), 0, 0);
  }

  static <N> DirectedNodeAdjacencies ofImmutable(
      Map<N, Adjacency> adjacentNodes, int predecessorCount, int successorCount) {
    return new DirectedNodeAdjacencies<N>(
        ImmutableMap.copyOf(adjacentNodes), predecessorCount, successorCount);
  }

  @Override
  public Set<N> adjacentNodes() {
    return Collections.unmodifiableSet(adjacentNodes.keySet());
  }

  @Override
  public Set<N> predecessors() {
    return new AbstractSet<N>() {
      @Override
      public Iterator<N> iterator() {
        final Iterator<Entry entries = adjacentNodes.entrySet().iterator();
        return new AbstractIterator<N>() {
          @Override
          protected N computeNext() {
            while (entries.hasNext()) {
              Entry<N, Adjacency> entry = entries.next();
              if (isPredecessor(entry.getValue())) {
                return entry.getKey();
              }
            }
            return endOfData();
          }
        };
      }

      @Override
      public int size() {
        return predecessorCount;
      }

      @Override
      public boolean contains(Object obj) {
        return isPredecessor(adjacentNodes.get(obj));
      }
    };
  }

  @Override
  public Set<N> successors() {
    return new AbstractSet<N>() {
      @Override
      public Iterator<N> iterator() {
        final Iterator<Entry entries = adjacentNodes.entrySet().iterator();
        return new AbstractIterator<N>() {
          @Override
          protected N computeNext() {
            while (entries.hasNext()) {
              Entry<N, Adjacency> entry = entries.next();
              if (isSuccessor(entry.getValue())) {
                return entry.getKey();
              }
            }
            return endOfData();
          }
        };
      }

      @Override
      public int size() {
        return successorCount;
      }

      @Override
      public boolean contains(Object obj) {
        return isSuccessor(adjacentNodes.get(obj));
      }
    };
  }

  @SuppressWarnings("unchecked") // Safe because we only cast if node is a key of Map<N, Adjacency>
  @Override
  public void removePredecessor(Object node) {
    checkNotNull(node, "node");
    Adjacency adjacency = adjacentNodes.get(node);
    if (adjacency == Adjacency.BOTH) {
      adjacentNodes.put((N) node, Adjacency.SUCC);
      predecessorCount--;
    } else if (adjacency == Adjacency.PRED) {
      adjacentNodes.remove(node);
      predecessorCount--;
    }
    checkState(predecessorCount >= 0);
  }

  @SuppressWarnings("unchecked") // Safe because we only cast if node is a key of Map<N, Adjacency>
  @Override
  public void removeSuccessor(Object node) {
    checkNotNull(node, "node");
    Adjacency adjacency = adjacentNodes.get(node);
    if (adjacency == Adjacency.BOTH) {
      adjacentNodes.put((N) node, Adjacency.PRED);
      successorCount--;
    } else if (adjacency == Adjacency.SUCC) {
      adjacentNodes.remove(node);
      successorCount--;
    }
    checkState(successorCount >= 0);
  }

  @Override
  public void addPredecessor(N node) {
    checkNotNull(node, "node");
    Adjacency adjacency = adjacentNodes.get(node);
    if (adjacency == null) {
      adjacentNodes.put(node, Adjacency.PRED);
      predecessorCount++;
    } else if (adjacency == Adjacency.SUCC) {
      adjacentNodes.put(node, Adjacency.BOTH);
      predecessorCount++;
    }
    checkState(predecessorCount >= 1);
  }

  @Override
  public void addSuccessor(N node) {
    checkNotNull(node, "node");
    Adjacency adjacency = adjacentNodes.get(node);
    if (adjacency == null) {
      adjacentNodes.put(node, Adjacency.SUCC);
      successorCount++;
    } else if (adjacency == Adjacency.PRED) {
      adjacentNodes.put(node, Adjacency.BOTH);
      successorCount++;
    }
    checkState(successorCount >= 1);
  }

  private static boolean isPredecessor(@Nullable Adjacency adjacency) {
    return (adjacency == Adjacency.PRED || adjacency == Adjacency.BOTH);
  }

  private static boolean isSuccessor(@Nullable Adjacency adjacency) {
    return (adjacency == Adjacency.SUCC || adjacency == Adjacency.BOTH);
  }
}

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