Consistently implement Iterable<T>

src/java/simpledb/Catalog.java

@@ -16,7 +16,7 @@
  * 
  * @Threadsafe
  */
-public class Catalog {
+public class Catalog implements Iterable<Integer> {
 
     /**
      * Constructor.
@@ -90,7 +90,10 @@ public String getPrimaryKey(int tableid) {
         return null;
     }
 
-    public Iterator<Integer> tableIdIterator() {
+    /**
+     * Returns an Iterator over the table IDs in this Catalog.
+     */
+    public Iterator<Integer> iterator() {
         // some code goes here
         return null;
     }

src/java/simpledb/HeapPage.java

@@ -11,7 +11,7 @@
  * @see BufferPool
  *
  */
-public class HeapPage implements Page {
+public class HeapPage implements Page, Iterable<Tuple> {
 
     final HeapPageId pid;
     final TupleDesc td;

src/java/simpledb/Tuple.java

@@ -9,7 +9,7 @@
  * specified schema specified by a TupleDesc object and contain Field objects
  * with the data for each field.
  */
-public class Tuple implements Serializable {
+public class Tuple implements Serializable, Iterable<Field> {
 
     private static final long serialVersionUID = 1L;
 
@@ -91,7 +91,7 @@ public String toString() {
      * @return
      *        An iterator which iterates over all the fields of this tuple
      * */
-    public Iterator<Field> fields()
+    public Iterator<Field> iterator()
     {
         // some code goes here
         return null;

src/java/simpledb/TupleDesc.java

@@ -6,7 +6,7 @@
 /**
  * TupleDesc describes the schema of a tuple.
  */
-public class TupleDesc implements Serializable {
+public class TupleDesc implements Serializable, Iterable<TDItem> {
 
     /**
      * A help class to facilitate organizing the information of each field