[Improve][Java] Make EdgesCollection and VerticesCollection support f…

…oreach loop (#270)

.github/workflows/java.yml

@@ -14,7 +14,6 @@ on:
     branches:
       - main
     paths:
-      - 'cpp/include/**'
       - 'java/**'
       - '.github/workflows/java.yml'
 

java/src/main/java/com/alibaba/graphar/edges/EdgesCollection.java

@@ -21,9 +21,10 @@
 import com.alibaba.graphar.stdcxx.StdString;
 import com.alibaba.graphar.types.AdjListType;
 import com.alibaba.graphar.util.Result;
+import java.util.Iterator;
 
 /** EdgesCollection is designed for reading a collection of edges. */
-public interface EdgesCollection extends CXXPointer {
+public interface EdgesCollection extends CXXPointer, Iterable<Edge> {
     /**
      * Construct the collection for a range of edges.
      *
@@ -129,4 +130,24 @@ static EdgesCollection create(
 
     /** Get the number of edges in the collection. */
     long size();
+
+    /** Implement Iterable interface to support for-each loop. */
+    default Iterator<Edge> iterator() {
+        return new Iterator<Edge>() {
+            EdgeIter current = begin();
+            EdgeIter end = end();
+
+            @Override
+            public boolean hasNext() {
+                return !current.isEnd();
+            }
+
+            @Override
+            public Edge next() {
+                Edge ret = current.get();
+                current.inc();
+                return ret;
+            }
+        };
+    }
 }

java/src/main/java/com/alibaba/graphar/vertices/VerticesCollection.java

@@ -27,12 +27,13 @@
 import com.alibaba.fastffi.FFITypeAlias;
 import com.alibaba.graphar.graphinfo.VertexInfo;
 import com.alibaba.graphar.stdcxx.StdString;
+import java.util.Iterator;
 
 /** VerticesCollection is designed for reading a collection of vertices. */
 @FFIGen
 @FFITypeAlias(GAR_VERTICES_COLLECTION)
 @CXXHead(GAR_GRAPH_H)
-public interface VerticesCollection extends CXXPointer {
+public interface VerticesCollection extends CXXPointer, Iterable<Vertex> {
 
     /** The iterator pointing to the first vertex. */
     @CXXValue
@@ -48,6 +49,26 @@ public interface VerticesCollection extends CXXPointer {
 
     long size();
 
+    /** Implement Iterable interface to support for-each loop. */
+    default Iterator<Vertex> iterator() {
+        return new Iterator<Vertex>() {
+            VertexIter current = begin();
+            VertexIter end = end();
+
+            @Override
+            public boolean hasNext() {
+                return !current.eq(end);
+            }
+
+            @Override
+            public Vertex next() {
+                Vertex ret = current.get();
+                current.inc();
+                return ret;
+            }
+        };
+    }
+
     @FFIFactory
     interface Factory {
         /**

java/src/test/java/com/alibaba/graphar/edges/EdgesCollectionTest.java

@@ -41,18 +41,18 @@ public void test1() {
                         AdjListType.ordered_by_source,
                         0,
                         1);
-        EdgeIter end = edges.end();
+        EdgeIter it = edges.begin();
         long count = 0L;
-        for (EdgeIter it = edges.begin(); !it.eq(end); it.inc()) {
+        for (Edge edge : edges) {
             // access data through iterator directly
             System.out.print("src=" + it.source() + ", dst=" + it.destination() + " ");
             // access data through edge
-            Edge edge = it.get();
             Assert.assertEquals(edge.source(), it.source());
             Assert.assertEquals(edge.destination(), it.destination());
             StdString creationDate = StdString.create("creationDate");
             System.out.println("creationDate=" + edge.property(creationDate, creationDate).value());
             count++;
+            it.inc();
         }
         System.out.println("edge_count=" + count);
         Assert.assertEquals(count, edges.size());
@@ -69,7 +69,7 @@ public void test1() {
                         4);
         EdgeIter end1 = edges1.end();
         long count1 = 0;
-        for (EdgeIter it = edges1.begin(); !it.eq(end1); it.inc()) {
+        for (Edge edge : edges1) {
             count1++;
         }
         System.out.println("edge_count=" + count1);
@@ -83,10 +83,8 @@ public void test1() {
                         edgeLabel.toJavaString(),
                         dstLabel.toJavaString(),
                         AdjListType.ordered_by_source);
-        EdgeIter end2 = edges2.end();
         long count2 = 0;
-        for (EdgeIter it = edges2.begin(); !it.eq(end2); it.inc()) {
-            Edge edge = it.get();
+        for (Edge edge : edges2) {
             System.out.println("src=" + edge.source() + ", dst=" + edge.destination());
             count2++;
         }
@@ -103,9 +101,8 @@ public void test1() {
                         AdjListType.unordered_by_source,
                         5,
                         5);
-        EdgeIter end3 = edges3.end();
         long count3 = 0;
-        for (EdgeIter it = edges3.begin(); !it.eq(end3); it.inc()) {
+        for (Edge edge : edges3) {
             count3++;
         }
         System.out.println("edge_count=" + count3);

java/src/test/java/com/alibaba/graphar/vertices/VerticesCollectionTest.java

@@ -40,7 +40,8 @@ public void test1() {
                 GrapharStaticFunctions.INSTANCE.constructVerticesCollection(graphInfo, label);
         Assert.assertFalse(maybeVerticesCollection.hasError());
         VerticesCollection vertices = maybeVerticesCollection.value();
-        for (VertexIter it = vertices.begin(); !it.eq(vertices.end()); it.inc()) {
+        VertexIter it = vertices.begin();
+        for (Vertex vertex : vertices) {
             // access data through iterator directly
             VertexIterGen itGen = (VertexIterGen) it;
             System.out.println(
@@ -50,7 +51,6 @@ public void test1() {
                             + ", firstName="
                             + it.property(property, property).value().toJavaString());
             // access data through vertex
-            Vertex vertex = it.get();
             System.out.println(
                     vertex.id()
                             + ", id="
@@ -66,6 +66,7 @@ public void test1() {
             Assert.assertEquals(
                     it.<StdString>property(property, property).value().toJavaString(),
                     vertex.<StdString>property(property, property).value().toJavaString());
+            it.inc();
         }
     }
 }