type param and misc.

src/main/java/graphql/relay/Connection.java

@@ -5,9 +5,9 @@
 /**
  * represents a connection in relay.
  */
-public interface Connection {
+public interface Connection<T> {
 
-    List<Edge> getEdges();
+    List<Edge<T>> getEdges();
 
     PageInfo getPageInfo();
 

src/main/java/graphql/relay/ConnectionCursor.java

@@ -1,7 +1,7 @@
 package graphql.relay;
 
 /**
- * represents a connection cursor in relay.
+ * represents a {@link Connection connection} cursor in relay.
  */
 public interface ConnectionCursor {
 

src/main/java/graphql/relay/DefaultConnection.java

@@ -1,20 +1,52 @@
 package graphql.relay;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
-public class DefaultConnection implements Connection {
+public class DefaultConnection<T> implements Connection<T> {
 
-    private List<Edge> edges = new ArrayList<Edge>();
+    private List<Edge<T>> edges = new ArrayList<Edge<T>>();
 
     private PageInfo pageInfo;
 
+    /**
+     * @deprecated prefer {@link #DefaultConnection(List, PageInfo)}
+     */
+    @Deprecated
+    public DefaultConnection() {
+    }
+
+    /**
+     * @param edges edges
+     * @param pageInfo page info
+     * @throws IllegalArgumentException if edges or page info is null. use {@link Collections#emptyList()} for empty edges.
+     */
+    public DefaultConnection(List<Edge<T>> edges, PageInfo pageInfo) {
+        if (edges == null) {
+            throw new IllegalArgumentException("edges cannot be empty");
+        }
+        if (pageInfo == null) {
+            throw new IllegalArgumentException("page info cannot be null");
+        }
+        // TODO make defensive copy
+        this.edges = edges;
+        this.pageInfo = pageInfo;
+    }
+
     @Override
-    public List<Edge> getEdges() {
-        return edges;
+    public List<Edge<T>> getEdges() {
+        return Collections.unmodifiableList(edges);
     }
 
-    public void setEdges(List<Edge> edges) {
+    /**
+     * @deprecated prefer {@link #DefaultConnection(List, PageInfo)} and avoid mutation
+     */
+    @Deprecated
+    public void setEdges(List<Edge<T>> edges) {
+        if (edges == null) { // TODO remove setter
+            edges = Collections.emptyList();
+        }
         this.edges = edges;
     }
 
@@ -23,6 +55,10 @@ public PageInfo getPageInfo() {
         return pageInfo;
     }
 
+    /**
+     * @deprecated prefer {@link #DefaultConnection(List, PageInfo)} and avoid mutation
+     */
+    @Deprecated
     public void setPageInfo(PageInfo pageInfo) {
         this.pageInfo = pageInfo;
     }

src/main/java/graphql/relay/DefaultEdge.java

@@ -1,21 +1,38 @@
 package graphql.relay;
 
-public class DefaultEdge implements Edge {
-
-    public DefaultEdge(Object node, DefaultConnectionCursor cursor) {
+public class DefaultEdge<T> implements Edge<T> {
+
+    public DefaultEdge(T node, ConnectionCursor cursor) {
+        if (node == null) {
+            throw new IllegalArgumentException("node cannot be null");
+        }
+        if (cursor == null) {
+            throw new IllegalArgumentException("cursor cannot be null");
+        }
         this.node = node;
         this.cursor = cursor;
     }
 
-    private Object node;
+    /**
+     * @deprecated prefer {@link #DefaultEdge(Object, ConnectionCursor)}
+     */
+    @Deprecated
+    public DefaultEdge() {
+    }
+
+    private T node;
     private ConnectionCursor cursor;
 
     @Override
-    public Object getNode() {
+    public T getNode() {
         return node;
     }
 
-    public void setNode(Object node) {
+    /**
+     * @deprecated prefer {@link #DefaultEdge(Object, ConnectionCursor)} and avoid mutation.
+     */
+    @Deprecated
+    public void setNode(T node) {
         this.node = node;
     }
 
@@ -24,6 +41,10 @@ public ConnectionCursor getCursor() {
         return cursor;
     }
 
+    /**
+     * @deprecated prefer {@link #DefaultEdge(Object, ConnectionCursor)} and avoid mutation.
+     */
+    @Deprecated
     public void setCursor(ConnectionCursor cursor) {
         this.cursor = cursor;
     }

src/main/java/graphql/relay/DefaultPageInfo.java

@@ -7,11 +7,29 @@ public class DefaultPageInfo implements PageInfo {
     private boolean hasPreviousPage;
     private boolean hasNextPage;
 
+    /**
+     * @deprecated prefer {@link #DefaultPageInfo(ConnectionCursor, ConnectionCursor, boolean, boolean)}
+     */
+    @Deprecated
+    public DefaultPageInfo() {
+    }
+
+    public DefaultPageInfo(ConnectionCursor startCursor, ConnectionCursor endCursor, boolean hasPreviousPage, boolean hasNextPage) {
+        this.startCursor = startCursor;
+        this.endCursor = endCursor;
+        this.hasPreviousPage = hasPreviousPage;
+        this.hasNextPage = hasNextPage;
+    }
+
     @Override
     public ConnectionCursor getStartCursor() {
         return startCursor;
     }
 
+    /**
+     * @deprecated prefer {@link #DefaultPageInfo(ConnectionCursor, ConnectionCursor, boolean, boolean)} and avoid mutation
+     */
+    @Deprecated
     public void setStartCursor(ConnectionCursor startCursor) {
         this.startCursor = startCursor;
     }
@@ -21,6 +39,10 @@ public ConnectionCursor getEndCursor() {
         return endCursor;
     }
 
+    /**
+     * @deprecated prefer {@link #DefaultPageInfo(ConnectionCursor, ConnectionCursor, boolean, boolean)} and avoid mutation
+     */
+    @Deprecated
     public void setEndCursor(ConnectionCursor endCursor) {
         this.endCursor = endCursor;
     }
@@ -30,6 +52,10 @@ public boolean isHasPreviousPage() {
         return hasPreviousPage;
     }
 
+    /**
+     * @deprecated prefer {@link #DefaultPageInfo(ConnectionCursor, ConnectionCursor, boolean, boolean)} and avoid mutation
+     */
+    @Deprecated
     public void setHasPreviousPage(boolean hasPreviousPage) {
         this.hasPreviousPage = hasPreviousPage;
     }
@@ -39,6 +65,10 @@ public boolean isHasNextPage() {
         return hasNextPage;
     }
 
+    /**
+     * @deprecated prefer {@link #DefaultPageInfo(ConnectionCursor, ConnectionCursor, boolean, boolean)}
+     */
+    @Deprecated
     public void setHasNextPage(boolean hasNextPage) {
         this.hasNextPage = hasNextPage;
     }

src/main/java/graphql/relay/Edge.java

@@ -3,9 +3,9 @@
 /**
  * represents an edge in relay.
  */
-public interface Edge {
+public interface Edge<T> {
 
-    Object getNode();
+    T getNode();
 
     ConnectionCursor getCursor();
 

src/main/java/graphql/relay/PageInfo.java

@@ -5,12 +5,23 @@
  */
 public interface PageInfo {
 
+    /**
+     * @return cursor to the first edge, or null if this page is empty.
+     */
     ConnectionCursor getStartCursor();
 
+    /**
+     * @return cursor to the last edge, or null if this page is empty.
+     */
     ConnectionCursor getEndCursor();
 
+    /**
+     * @return true if and only if this page is not the first page. only meaningful when you gave {@code last} argument.
+     */
     boolean isHasPreviousPage();
 
+    /**
+     * @return true if and only if this page is not the last page. only meaningful when you gave {@code first} argument.
+     */
     boolean isHasNextPage();
-
 }

src/main/java/graphql/relay/Relay.java

@@ -17,6 +17,7 @@
 public class Relay {
 
     public static final String NODE = "Node";
+
     private GraphQLObjectType pageInfoType = newObject()
             .name("PageInfo")
             .description("Information about pagination in a connection.")
@@ -39,7 +40,7 @@ public class Relay {
             .build();
 
     public GraphQLInterfaceType nodeInterface(TypeResolver typeResolver) {
-        GraphQLInterfaceType node = newInterface()
+        return newInterface()
                 .name(NODE)
                 .description("An object with an ID")
                 .typeResolver(typeResolver)
@@ -48,11 +49,10 @@ public GraphQLInterfaceType nodeInterface(TypeResolver typeResolver) {
                         .description("The ID of an object")
                         .type(new GraphQLNonNull(GraphQLID)))
                 .build();
-        return node;
     }
 
     public GraphQLFieldDefinition nodeField(GraphQLInterfaceType nodeInterface, DataFetcher nodeDataFetcher) {
-        GraphQLFieldDefinition fieldDefinition = newFieldDefinition()
+        return newFieldDefinition()
                 .name("node")
                 .description("Fetches an object given its ID")
                 .type(nodeInterface)
@@ -62,91 +62,93 @@ public GraphQLFieldDefinition nodeField(GraphQLInterfaceType nodeInterface, Data
                         .description("The ID of an object")
                         .type(new GraphQLNonNull(GraphQLID)))
                 .build();
-        return fieldDefinition;
     }
 
     public List<GraphQLArgument> getConnectionFieldArguments() {
         List<GraphQLArgument> args = new ArrayList<GraphQLArgument>();
-
         args.add(newArgument()
                 .name("before")
+                .description("fetching only nodes before this node (exclusive)")
                 .type(GraphQLString)
                 .build());
         args.add(newArgument()
                 .name("after")
+                .description("fetching only nodes after this node (exclusive)")
                 .type(GraphQLString)
                 .build());
         args.add(newArgument()
                 .name("first")
+                .description("fetching only the first certain number of nodes")
                 .type(GraphQLInt)
                 .build());
         args.add(newArgument()
                 .name("last")
+                .description("fetching only the last certain number of nodes")
                 .type(GraphQLInt)
                 .build());
         return args;
     }
 
     public List<GraphQLArgument> getBackwardPaginationConnectionFieldArguments() {
         List<GraphQLArgument> args = new ArrayList<GraphQLArgument>();
-
         args.add(newArgument()
                 .name("before")
+                .description("fetching only nodes before this node (exclusive)")
                 .type(GraphQLString)
                 .build());
         args.add(newArgument()
                 .name("last")
+                .description("fetching only the last certain number of nodes")
                 .type(GraphQLInt)
                 .build());
         return args;
     }
 
     public List<GraphQLArgument> getForwardPaginationConnectionFieldArguments() {
         List<GraphQLArgument> args = new ArrayList<GraphQLArgument>();
-
         args.add(newArgument()
                 .name("after")
+                .description("fetching only nodes after this node (exclusive)")
                 .type(GraphQLString)
                 .build());
         args.add(newArgument()
                 .name("first")
+                .description("fetching only the first certain number of nodes")
                 .type(GraphQLInt)
                 .build());
         return args;
     }
 
     public GraphQLObjectType edgeType(String name, GraphQLOutputType nodeType, GraphQLInterfaceType nodeInterface, List<GraphQLFieldDefinition> edgeFields) {
-
-        GraphQLObjectType edgeType = newObject()
+        return newObject()
                 .name(name + "Edge")
-                .description("An edge in a connection.")
+                .description("An edge in a connection")
                 .field(newFieldDefinition()
                         .name("node")
                         .type(nodeType)
                         .description("The item at the end of the edge"))
                 .field(newFieldDefinition()
                         .name("cursor")
                         .type(new GraphQLNonNull(GraphQLString))
-                        .description(""))
+                        .description("cursor marks a unique position or index into the connection"))
                 .fields(edgeFields)
                 .build();
-        return edgeType;
     }
 
     public GraphQLObjectType connectionType(String name, GraphQLObjectType edgeType, List<GraphQLFieldDefinition> connectionFields) {
-
-        GraphQLObjectType connectionType = newObject()
+        return newObject()
                 .name(name + "Connection")
                 .description("A connection to a list of items.")
                 .field(newFieldDefinition()
                         .name("edges")
+                        .description("a list of edges")
                         .type(new GraphQLList(edgeType)))
                 .field(newFieldDefinition()
                         .name("pageInfo")
+                        .description("details about this specific page")
                         .type(new GraphQLNonNull(pageInfoType)))
                 .fields(connectionFields)
                 .build();
-        return connectionType;
     }