[SMALLFIX] Simplify return type of getBlockIterator

servers/src/main/java/tachyon/worker/block/evictor/EvictorBase.java

@@ -18,16 +18,15 @@
 import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
-import java.util.Map;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import com.google.common.base.Preconditions;
 
 import tachyon.Constants;
-import tachyon.collections.Pair;
 import tachyon.Sessions;
+import tachyon.collections.Pair;
 import tachyon.exception.BlockDoesNotExistException;
 import tachyon.worker.block.BlockMetadataManagerView;
 import tachyon.worker.block.BlockStoreEventListenerBase;
@@ -84,9 +83,9 @@ protected StorageDirView cascadingEvict(long bytesToBeAvailable, BlockStoreLocat
     // 2. Iterate over blocks in order until we find a StorageDirView that is in the range of
     // location and can satisfy bytesToBeAvailable after evicting its blocks iterated so far
     EvictionDirCandidates dirCandidates = new EvictionDirCandidates();
-    Iterator<Map.Entry<Long, Object>> it = getBlockIterator();
+    Iterator<Long> it = getBlockIterator();
     while (it.hasNext() && dirCandidates.candidateSize() < bytesToBeAvailable) {
-      long blockId = it.next().getKey();
+      long blockId = it.next();
       try {
         BlockMeta block = mManagerView.getBlockMeta(blockId);
         if (block != null) { // might not present in this view
@@ -183,12 +182,11 @@ public EvictionPlan freeSpaceWithView(long bytesToBeAvailable, BlockStoreLocatio
   }
 
   /**
-   * @return an iterator over the blocks in the evictor cache. The evictor is responsible for
-   * specifying the iteration order using its own strategy. For example, LRUEvictor returns an
-   * iterator that iterates the blocks in LRU order. The key of the map entry is the block Id.
+   * @return an iterator over the IDs of the blocks in the evictor cache. The evictor is responsible
+   * for specifying the iteration order using its own strategy. For example, LRUEvictor returns an
+   * iterator that iterates through the block IDs in LRU order.
    */
-  // TODO(calvin): Is a key iterator sufficient?
-  protected abstract Iterator<Map.Entry<Long, Object>> getBlockIterator();
+  protected abstract Iterator<Long> getBlockIterator();
 
   /**
    * Perform additional cleanup when a block is removed from the iterator returned by

servers/src/main/java/tachyon/worker/block/evictor/LRFUEvictor.java

@@ -25,7 +25,9 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicLong;
 
+import com.google.common.base.Function;
 import com.google.common.base.Preconditions;
+import com.google.common.collect.Iterators;
 
 import tachyon.Constants;
 import tachyon.collections.Pair;
@@ -123,8 +125,14 @@ public EvictionPlan freeSpaceWithView(long bytesToBeAvailable, BlockStoreLocatio
   }
 
   @Override
-  protected Iterator<Map.Entry<Long, Object>> getBlockIterator() {
-    return (Iterator) getSortedCRF().iterator();
+  protected Iterator<Long> getBlockIterator() {
+    return Iterators.transform(getSortedCRF().iterator(),
+        new Function<Map.Entry<Long, Double>, Long>() {
+          @Override
+          public Long apply(Entry<Long, Double> input) {
+            return input.getKey();
+          }
+        });
   }
 
   /**

servers/src/main/java/tachyon/worker/block/evictor/LRUEvictor.java

@@ -60,8 +60,8 @@ public LRUEvictor(BlockMetadataManagerView view, Allocator allocator) {
   }
 
   @Override
-  protected Iterator<Map.Entry<Long, Object>> getBlockIterator() {
-    return (Iterator) mLRUCache.entrySet().iterator();
+  protected Iterator<Long> getBlockIterator() {
+    return mLRUCache.keySet().iterator();
   }
 
   @Override