Skiplist iterator

README.md

@@ -91,7 +91,7 @@ To locate an element, we start from the top level and move forward until we find
 we are looking for. Then we move down to the next level and repeat the process until we find the element.
 
 Insertions, deletions, and updates are done by first locating the element, then performing
-the operation on the node. All of them have a time complexity of `O(log(n))`.
+the operation on the node. All of them have an average time complexity of `O(log(n))`.
 
 ---
 

src/main/java/com/tomfran/lsm/memtable/SkipList.java

@@ -9,19 +9,33 @@
 import static java.lang.Math.ceil;
 import static java.lang.Math.log;
 
+/**
+ * A skip list implementation of items.
+ */
 public class SkipList implements Iterable<Item> {
 
     static final int DEFAULT_ELEMENTS = 1 << 16;
+
     final Node sentinel;
+
     private final Node[] buffer;
     private final XoRoShiRo128PlusRandom rn;
+
     int levels;
     int size;
 
+    /**
+     * Create a skip list with a default number of elements, 2 ^ 16.
+     */
     public SkipList() {
         this(DEFAULT_ELEMENTS);
     }
 
+    /**
+     * Create a skip list with a specified number of elements.
+     *
+     * @param numElements The number of elements to size the skip list for.
+     */
     public SkipList(int numElements) {
         levels = (int) ceil(log(numElements) / log(2));
         size = 0;
@@ -30,6 +44,11 @@ public SkipList(int numElements) {
         buffer = new Node[levels];
     }
 
+    /**
+     * Add an item to the skip list.
+     *
+     * @param item The item to add.
+     */
     public void add(Item item) {
         Node current = sentinel;
         for (int i = levels - 1; i >= 0; i--) {
@@ -58,6 +77,12 @@ private int randomLevel() {
         return level;
     }
 
+    /**
+     * Retrieve an item from the skip list.
+     *
+     * @param key The key of the item to retrieve.
+     * @return The item if found, null otherwise.
+     */
     public Item get(byte[] key) {
         Node current = sentinel;
         for (int i = levels - 1; i >= 0; i--) {
@@ -71,6 +96,11 @@ public Item get(byte[] key) {
         return null;
     }
 
+    /**
+     * Remove an item from the skip list.
+     *
+     * @param key The key of the item to remove.
+     */
     public void remove(byte[] key) {
         Node current = sentinel;
         for (int i = levels - 1; i >= 0; i--) {
@@ -90,13 +120,23 @@ public void remove(byte[] key) {
         }
     }
 
+    /**
+     * Get the number of items in the skip list.
+     *
+     * @return Skip list size.
+     */
     public int size() {
         return size;
     }
 
+    /**
+     * Get an iterator over the items in the skip list at the lowest level.
+     *
+     * @return An iterator over the items in the skip list.
+     */
     @Override
     public Iterator<Item> iterator() {
-        return null;
+        return new SkipListIterator(sentinel);
     }
 
     @Override
@@ -114,7 +154,7 @@ public String toString() {
         return sb.toString();
     }
 
-    static final class Node {
+    private static final class Node {
         Item value;
         Node[] next;
 
@@ -124,4 +164,17 @@ static final class Node {
         }
     }
 
+    private record SkipListIterator(Node node) implements Iterator<Item> {
+
+        @Override
+        public boolean hasNext() {
+            return node.next[0] != null;
+        }
+
+        @Override
+        public Item next() {
+            return node.next[0].value;
+        }
+    }
+
 }

src/main/java/com/tomfran/lsm/sstable/SSTable.java

@@ -205,13 +205,7 @@ private void writeItems(String filename, Iterable<Item> items, int sampleSize, i
         indexOs.close();
     }
 
-    private static class SSTableIterator implements Iterator<Item> {
-
-        private final SSTable table;
-
-        public SSTableIterator(SSTable table) {
-            this.table = table;
-        }
+    private record SSTableIterator(SSTable table) implements Iterator<Item> {
 
         @Override
         public boolean hasNext() {
@@ -233,7 +227,7 @@ public Item next() {
      */
     private static class SSTableMergerIterator extends IteratorMerger<Item> implements Iterable<Item> {
 
-        private Item last, next;
+        private Item last;
 
         @SafeVarargs
         public SSTableMergerIterator(Iterator<Item>... iterators) {
@@ -248,7 +242,7 @@ public boolean hasNext() {
 
         @Override
         public Item next() {
-            next = super.next();
+            Item next = super.next();
             while (next != null && last.compareTo(next) == 0)
                 next = super.next();