Add the method Graphs.endpoints() that does what you expect: returns …

…the endpoints corresponding to each edge in a graph. The whole "we print every edge in an undirected graph's toString() twice, and that's a feature not a bug *wink*" annoyed me. Also there's other cases, such as copyOf() and and getWeaklyConnectedComponents(), where we don't want to process each edge twice. In those particular cases they happen to be no-ops, but for cases where it's not, or where you do something computationally expensive, doubling up on undirected edges is bad :(

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=126884706

guava-tests/test/com/google/common/graph/GraphsTest.java

@@ -31,6 +31,7 @@
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
 
+import java.util.Collection;
 import java.util.Set;
 
 /**
@@ -39,6 +40,7 @@
  */
 @RunWith(JUnit4.class)
 public class GraphsTest {
+  private static final Integer N0 = 0;
   private static final Integer N1 = 1;
   private static final Integer N2 = 2;
   private static final Integer N3 = 3;
@@ -129,7 +131,6 @@ public void roots_multipleRoots() {
     assertThat(roots(directedGraph)).isEqualTo(ImmutableSet.of(N1, N2));
   }
 
-  @Test
   public void parallelEdges_directed() {
     MutableNetwork<Integer, String> directedGraph =
         NetworkBuilder.directed().allowsParallelEdges(true).build();
@@ -480,4 +481,12 @@ private static MutableNetwork<Integer, String> buildUndirectedTestNetwork() {
 
     return undirectedGraph;
   }
+
+  private static void containsExactlySanityCheck(Collection<?> collection, Object... varargs) {
+    assertThat(collection).hasSize(varargs.length);
+    for (Object obj : varargs) {
+      assertThat(collection).contains(obj);
+    }
+    assertThat(collection).containsExactly(varargs);
+  }
 }

guava/src/com/google/common/graph/AbstractGraph.java

@@ -34,19 +34,19 @@ public abstract class AbstractGraph<N> implements Graph<N> {
 
   @Override
   public int degree(Object node) {
-    // only works for non-multigraphs; multigraphs not yet supported
+    // TODO(b/28087289): only works for non-multigraphs; multigraphs not yet supported
     return adjacentNodes(node).size();
   }
 
   @Override
   public int inDegree(Object node) {
-    // only works for non-multigraphs; multigraphs not yet supported
+    // TODO(b/28087289): only works for non-multigraphs; multigraphs not yet supported
     return predecessors(node).size();
   }
 
   @Override
   public int outDegree(Object node) {
-    // only works for non-multigraphs; multigraphs not yet supported
+    // TODO(b/28087289): only works for non-multigraphs; multigraphs not yet supported
     return successors(node).size();
   }