[FLINK-4646] [gelly] Add BipartiateGraph

This closes apache#2564

flink-libraries/flink-gelly/src/main/java/org/apache/flink/graph/Edge.java

@@ -34,10 +34,10 @@ public class Edge<K, V> extends Tuple3<K, K, V>{
 
 	public Edge(){}
 
-	public Edge(K src, K trg, V val) {
-		this.f0 = src;
-		this.f1 = trg;
-		this.f2 = val;
+	public Edge(K source, K target, V value) {
+		this.f0 = source;
+		this.f1 = target;
+		this.f2 = value;
 	}
 
 	/**
@@ -49,8 +49,8 @@ public Edge<K, V> reverse() {
 			return new Edge<>(this.f1, this.f0, this.f2);
 	}
 
-	public void setSource(K src) {
-		this.f0 = src;
+	public void setSource(K source) {
+		this.f0 = source;
 	}
 
 	public K getSource() {

flink-libraries/flink-gelly/src/main/java/org/apache/flink/graph/bipartite/BipartiteEdge.java

@@ -0,0 +1,68 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.flink.graph.bipartite;
+
+import org.apache.flink.api.java.tuple.Tuple3;
+import org.apache.flink.graph.Edge;
+
+/**
+ * A BipartiteEdge represents a link between top and bottom vertices
+ * in a {@link BipartiteGraph}. It is generalized form of {@link Edge}
+ * where the source and target vertex IDs can be of different types.
+ *
+ * @param <KT> the key type of the top vertices
+ * @param <KB> the key type of the bottom vertices
+ * @param <EV> the edge value type
+ */
+public class BipartiteEdge<KT, KB, EV> extends Tuple3<KT, KB, EV> {
+
+	private static final long serialVersionUID = 1L;
+
+	public BipartiteEdge() {}
+
+	public BipartiteEdge(KT topId, KB bottomId, EV value) {
+		this.f0 = topId;
+		this.f1 = bottomId;
+		this.f2 = value;
+	}
+
+	public KT getTopId() {
+		return this.f0;
+	}
+
+	public void setTopId(KT topId) {
+		this.f0 = topId;
+	}
+
+	public KB getBottomId() {
+		return this.f1;
+	}
+
+	public void setBottomId(KB bottomId) {
+		this.f1 = bottomId;
+	}
+
+	public EV getValue() {
+		return this.f2;
+	}
+
+	public void setValue(EV value) {
+		this.f2 = value;
+	}
+}