diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 3dc53a4ba98..074c7ff1c32 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -36,6 +36,9 @@ Release 2.4.0 - UNRELEASED
     HDFS-5940. Minor cleanups to ShortCircuitReplica, FsDatasetCache, and
     DomainSocketWatcher (cmccabe)
 
+    HDFS-5531. Combine the getNsQuota() and getDsQuota() methods in INode.
+    (szetszwo)
+
   OPTIMIZATIONS
 
     HDFS-5790. LeaseManager.findPath is very slow when many leases need recovery
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/Content.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/Content.java
index 5dfa3e952f5..c1caae52ec0 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/Content.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/Content.java
@@ -47,7 +47,7 @@ public static Counts newInstance() {
     }
 
     private Counts() {
-      super(Content.values());
+      super(Content.class);
     }
   }
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirectory.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirectory.java
index 8b9fad1a548..658b938de96 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirectory.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirectory.java
@@ -2448,8 +2448,9 @@ INodeDirectory unprotectedSetQuota(String src, long nsQuota, long dsQuota)
     if (dirNode.isRoot() && nsQuota == HdfsConstants.QUOTA_RESET) {
       throw new IllegalArgumentException("Cannot clear namespace quota on root.");
     } else { // a directory inode
-      long oldNsQuota = dirNode.getNsQuota();
-      long oldDsQuota = dirNode.getDsQuota();
+      final Quota.Counts oldQuota = dirNode.getQuotaCounts();
+      final long oldNsQuota = oldQuota.get(Quota.NAMESPACE);
+      final long oldDsQuota = oldQuota.get(Quota.DISKSPACE);
       if (nsQuota == HdfsConstants.QUOTA_DONT_SET) {
         nsQuota = oldNsQuota;
       }
@@ -2501,8 +2502,9 @@ void setQuota(String src, long nsQuota, long dsQuota)
     try {
       INodeDirectory dir = unprotectedSetQuota(src, nsQuota, dsQuota);
       if (dir != null) {
-        fsImage.getEditLog().logSetQuota(src, dir.getNsQuota(), 
-                                         dir.getDsQuota());
+        final Quota.Counts q = dir.getQuotaCounts();
+        fsImage.getEditLog().logSetQuota(src,
+            q.get(Quota.NAMESPACE), q.get(Quota.DISKSPACE));
       }
     } finally {
       writeUnlock();
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImage.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImage.java
index 6d01e80b2e4..ee11279a5ae 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImage.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImage.java
@@ -784,18 +784,22 @@ private static void updateCountForQuotaRecursively(INodeDirectory dir,
       
     if (dir.isQuotaSet()) {
       // check if quota is violated. It indicates a software bug.
+      final Quota.Counts q = dir.getQuotaCounts();
+
       final long namespace = counts.get(Quota.NAMESPACE) - parentNamespace;
-      if (Quota.isViolated(dir.getNsQuota(), namespace)) {
+      final long nsQuota = q.get(Quota.NAMESPACE);
+      if (Quota.isViolated(nsQuota, namespace)) {
         LOG.error("BUG: Namespace quota violation in image for "
             + dir.getFullPathName()
-            + " quota = " + dir.getNsQuota() + " < consumed = " + namespace);
+            + " quota = " + nsQuota + " < consumed = " + namespace);
       }
 
       final long diskspace = counts.get(Quota.DISKSPACE) - parentDiskspace;
-      if (Quota.isViolated(dir.getDsQuota(), diskspace)) {
+      final long dsQuota = q.get(Quota.DISKSPACE);
+      if (Quota.isViolated(dsQuota, diskspace)) {
         LOG.error("BUG: Diskspace quota violation in image for "
             + dir.getFullPathName()
-            + " quota = " + dir.getDsQuota() + " < consumed = " + diskspace);
+            + " quota = " + dsQuota + " < consumed = " + diskspace);
       }
 
       ((INodeDirectoryWithQuota)dir).setSpaceConsumed(namespace, diskspace);
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImageFormat.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImageFormat.java
index 18032d9edab..fb18f68f564 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImageFormat.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImageFormat.java
@@ -383,8 +383,9 @@ void load(File curFile) throws IOException {
 
   /** Update the root node's attributes */
   private void updateRootAttr(INodeWithAdditionalFields root) {                                                           
-    long nsQuota = root.getNsQuota();
-    long dsQuota = root.getDsQuota();
+    final Quota.Counts q = root.getQuotaCounts();
+    final long nsQuota = q.get(Quota.NAMESPACE);
+    final long dsQuota = q.get(Quota.DISKSPACE);
     FSDirectory fsDir = namesystem.dir;
     if (nsQuota != -1 || dsQuota != -1) {
       fsDir.rootDir.setQuota(nsQuota, dsQuota);
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImageSerialization.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImageSerialization.java
index e27a2f1df44..654bc55bb63 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImageSerialization.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImageSerialization.java
@@ -226,6 +226,12 @@ public static void writeINodeFileAttributes(INodeFileAttributes file,
     out.writeLong(file.getPreferredBlockSize());
   }
 
+  private static void writeQuota(Quota.Counts quota, DataOutput out)
+      throws IOException {
+    out.writeLong(quota.get(Quota.NAMESPACE));
+    out.writeLong(quota.get(Quota.DISKSPACE));
+  }
+
   /**
    * Serialize a {@link INodeDirectory}
    * @param node The node to write
@@ -241,8 +247,8 @@ public static void writeINodeDirectory(INodeDirectory node, DataOutput out)
     out.writeLong(0);   // preferred block size
     out.writeInt(-1);   // # of blocks
 
-    out.writeLong(node.getNsQuota());
-    out.writeLong(node.getDsQuota());
+    writeQuota(node.getQuotaCounts(), out);
+
     if (node instanceof INodeDirectorySnapshottable) {
       out.writeBoolean(true);
     } else {
@@ -263,9 +269,7 @@ public static void writeINodeDirectoryAttributes(
     writeLocalName(a, out);
     writePermissionStatus(a, out);
     out.writeLong(a.getModificationTime());
-
-    out.writeLong(a.getNsQuota());
-    out.writeLong(a.getDsQuota());
+    writeQuota(a.getQuotaCounts(), out);
   }
 
   /**
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INode.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INode.java
index 1aff9784aba..e5f26b08b1e 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INode.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INode.java
@@ -383,10 +383,11 @@ public final ContentSummary computeContentSummary() {
   public final ContentSummary computeAndConvertContentSummary(
       ContentSummaryComputationContext summary) {
     Content.Counts counts = computeContentSummary(summary).getCounts();
+    final Quota.Counts q = getQuotaCounts();
     return new ContentSummary(counts.get(Content.LENGTH),
         counts.get(Content.FILE) + counts.get(Content.SYMLINK),
-        counts.get(Content.DIRECTORY), getNsQuota(),
-        counts.get(Content.DISKSPACE), getDsQuota());
+        counts.get(Content.DIRECTORY), q.get(Quota.NAMESPACE),
+        counts.get(Content.DISKSPACE), q.get(Quota.DISKSPACE));
   }
 
   /**
@@ -412,18 +413,15 @@ public void addSpaceConsumed(long nsDelta, long dsDelta, boolean verify)
 
   /**
    * Get the quota set for this inode
-   * @return the quota if it is set; -1 otherwise
+   * @return the quota counts.  The count is -1 if it is not set.
    */
-  public long getNsQuota() {
-    return -1;
-  }
-
-  public long getDsQuota() {
-    return -1;
+  public Quota.Counts getQuotaCounts() {
+    return Quota.Counts.newInstance(-1, -1);
   }
   
   public final boolean isQuotaSet() {
-    return getNsQuota() >= 0 || getDsQuota() >= 0;
+    final Quota.Counts q = getQuotaCounts();
+    return q.get(Quota.NAMESPACE) >= 0 || q.get(Quota.DISKSPACE) >= 0;
   }
   
   /**
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectory.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectory.java
index 0355b307c42..8133de46985 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectory.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectory.java
@@ -612,8 +612,7 @@ public Quota.Counts cleanSubtree(final Snapshot snapshot, Snapshot prior,
   @Override
   public boolean metadataEquals(INodeDirectoryAttributes other) {
     return other != null
-        && getNsQuota() == other.getNsQuota()
-        && getDsQuota() == other.getDsQuota()
+        && getQuotaCounts().equals(other.getQuotaCounts())
         && getPermissionLong() == other.getPermissionLong();
   }
   
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectoryAttributes.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectoryAttributes.java
index 5bff5cdaf51..b0ea44bd811 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectoryAttributes.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectoryAttributes.java
@@ -27,9 +27,7 @@
  */
 @InterfaceAudience.Private
 public interface INodeDirectoryAttributes extends INodeAttributes {
-  public long getNsQuota();
-
-  public long getDsQuota();
+  public Quota.Counts getQuotaCounts();
 
   public boolean metadataEquals(INodeDirectoryAttributes other);
   
@@ -46,20 +44,14 @@ public SnapshotCopy(INodeDirectory dir) {
     }
 
     @Override
-    public long getNsQuota() {
-      return -1;
-    }
-
-    @Override
-    public long getDsQuota() {
-      return -1;
+    public Quota.Counts getQuotaCounts() {
+      return Quota.Counts.newInstance(-1, -1);
     }
 
     @Override
     public boolean metadataEquals(INodeDirectoryAttributes other) {
       return other != null
-          && getNsQuota() == other.getNsQuota()
-          && getDsQuota() == other.getDsQuota()
+          && this.getQuotaCounts().equals(other.getQuotaCounts())
           && getPermissionLong() == other.getPermissionLong();
     }
   }
@@ -68,6 +60,7 @@ public static class CopyWithQuota extends INodeDirectoryAttributes.SnapshotCopy
     private final long nsQuota;
     private final long dsQuota;
 
+
     public CopyWithQuota(byte[] name, PermissionStatus permissions,
         long modificationTime, long nsQuota, long dsQuota) {
       super(name, permissions, modificationTime);
@@ -78,18 +71,14 @@ public CopyWithQuota(byte[] name, PermissionStatus permissions,
     public CopyWithQuota(INodeDirectory dir) {
       super(dir);
       Preconditions.checkArgument(dir.isQuotaSet());
-      this.nsQuota = dir.getNsQuota();
-      this.dsQuota = dir.getDsQuota();
+      final Quota.Counts q = dir.getQuotaCounts();
+      this.nsQuota = q.get(Quota.NAMESPACE);
+      this.dsQuota = q.get(Quota.DISKSPACE);
     }
     
     @Override
-    public final long getNsQuota() {
-      return nsQuota;
-    }
-
-    @Override
-    public final long getDsQuota() {
-      return dsQuota;
+    public Quota.Counts getQuotaCounts() {
+      return Quota.Counts.newInstance(nsQuota, dsQuota);
     }
   }
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectoryWithQuota.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectoryWithQuota.java
index e18420df4fb..41f1984f77e 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectoryWithQuota.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectoryWithQuota.java
@@ -44,7 +44,7 @@ public class INodeDirectoryWithQuota extends INodeDirectory {
    * @param dsQuota Diskspace quota to be assigned to this indoe
    * @param other The other inode from which all other properties are copied
    */
-  public INodeDirectoryWithQuota(INodeDirectory other, boolean adopt,
+  INodeDirectoryWithQuota(INodeDirectory other, boolean adopt,
       long nsQuota, long dsQuota) {
     super(other, adopt);
     final Quota.Counts counts = other.computeQuotaUsage();
@@ -54,6 +54,11 @@ public INodeDirectoryWithQuota(INodeDirectory other, boolean adopt,
     this.dsQuota = dsQuota;
   }
   
+  public INodeDirectoryWithQuota(INodeDirectory other, boolean adopt,
+      Quota.Counts quota) {
+    this(other, adopt, quota.get(Quota.NAMESPACE), quota.get(Quota.DISKSPACE));
+  }
+
   /** constructor with no quota verification */
   INodeDirectoryWithQuota(long id, byte[] name, PermissionStatus permissions,
       long modificationTime, long nsQuota, long dsQuota) {
@@ -67,20 +72,9 @@ public INodeDirectoryWithQuota(INodeDirectory other, boolean adopt,
     super(id, name, permissions, 0L);
   }
   
-  /** Get this directory's namespace quota
-   * @return this directory's namespace quota
-   */
   @Override
-  public long getNsQuota() {
-    return nsQuota;
-  }
-  
-  /** Get this directory's diskspace quota
-   * @return this directory's diskspace quota
-   */
-  @Override
-  public long getDsQuota() {
-    return dsQuota;
+  public Quota.Counts getQuotaCounts() {
+    return Quota.Counts.newInstance(nsQuota, dsQuota);
   }
   
   /** Set this directory's quota
@@ -120,7 +114,7 @@ public ContentSummaryComputationContext computeContentSummary(
   }
   
   private void checkDiskspace(final long computed) {
-    if (-1 != getDsQuota() && diskspace != computed) {
+    if (-1 != getQuotaCounts().get(Quota.DISKSPACE) && diskspace != computed) {
       NameNode.LOG.error("BUG: Inconsistent diskspace for directory "
           + getFullPathName() + ". Cached = " + diskspace
           + " != Computed = " + computed);
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeReference.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeReference.java
index a049c012917..f77863ada85 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeReference.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeReference.java
@@ -295,15 +295,10 @@ public final INodeAttributes getSnapshotINode(Snapshot snapshot) {
   }
 
   @Override
-  public final long getNsQuota() {
-    return referred.getNsQuota();
+  public Quota.Counts getQuotaCounts() {
+    return referred.getQuotaCounts();
   }
 
-  @Override
-  public final long getDsQuota() {
-    return referred.getDsQuota();
-  }
-  
   @Override
   public final void clear() {
     super.clear();
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NamenodeJspHelper.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NamenodeJspHelper.java
index 564df85468e..5a25d4fea2d 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NamenodeJspHelper.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NamenodeJspHelper.java
@@ -23,7 +23,6 @@
 import java.lang.management.ManagementFactory;
 import java.lang.management.MemoryMXBean;
 import java.lang.management.MemoryUsage;
-import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.URI;
 import java.net.URLEncoder;
@@ -63,7 +62,6 @@
 import org.apache.hadoop.hdfs.server.namenode.startupprogress.Step;
 import org.apache.hadoop.hdfs.server.namenode.startupprogress.StepType;
 import org.apache.hadoop.hdfs.server.protocol.NamenodeProtocols;
-import org.apache.hadoop.http.HttpConfig;
 import org.apache.hadoop.io.Text;
 import org.apache.hadoop.net.NodeBase;
 import org.apache.hadoop.security.UserGroupInformation;
@@ -1090,7 +1088,7 @@ public void toXML(XMLOutputter doc) throws IOException {
           doc.endTag();
 
           doc.startTag("ds_quota");
-          doc.pcdata(""+inode.getDsQuota());
+          doc.pcdata(""+inode.getQuotaCounts().get(Quota.DISKSPACE));
           doc.endTag();
 
           doc.startTag("permission_status");
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/Quota.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/Quota.java
index 36e803a149b..7abd017dac2 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/Quota.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/Quota.java
@@ -41,7 +41,7 @@ public static Counts newInstance() {
     }
     
     Counts() {
-      super(Quota.values());
+      super(Quota.class);
     }
   }
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/snapshot/INodeDirectoryWithSnapshot.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/snapshot/INodeDirectoryWithSnapshot.java
index 6263a96b380..bb137e9b283 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/snapshot/INodeDirectoryWithSnapshot.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/snapshot/INodeDirectoryWithSnapshot.java
@@ -487,7 +487,7 @@ public INodeDirectoryWithSnapshot(INodeDirectory that) {
 
   INodeDirectoryWithSnapshot(INodeDirectory that, boolean adopt,
       DirectoryDiffList diffs) {
-    super(that, adopt, that.getNsQuota(), that.getDsQuota());
+    super(that, adopt, that.getQuotaCounts());
     this.diffs = diffs != null? diffs: new DirectoryDiffList();
   }
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/EnumCounters.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/EnumCounters.java
index 1df4e1811ee..e3975f6d68a 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/EnumCounters.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/EnumCounters.java
@@ -17,6 +17,7 @@
  */
 package org.apache.hadoop.hdfs.util;
 
+import java.util.Arrays;
 import java.util.HashMap;
 
 import com.google.common.base.Preconditions;
@@ -34,21 +35,19 @@
  * @param <E> the enum type
  */
 public class EnumCounters<E extends Enum<E>> {
-  /** An array of enum constants. */
-  private final E[] enumConstants;
+  /** The class of the enum. */
+  private final Class<E> enumClass;
   /** The counter array, counters[i] corresponds to the enumConstants[i]. */
   private final long[] counters;
 
   /**
    * Construct counters for the given enum constants.
-   * @param enumConstants an array of enum constants such that, 
-   *                      for all i, enumConstants[i].ordinal() == i.
+   * @param enumClass the enum class of the counters.
    */
-  public EnumCounters(final E[] enumConstants) {
-    for(int i = 0; i < enumConstants.length; i++) {
-      Preconditions.checkArgument(enumConstants[i].ordinal() == i);
-    }
-    this.enumConstants = enumConstants;
+  public EnumCounters(final Class<E> enumClass) {
+    final E[] enumConstants = enumClass.getEnumConstants();
+    Preconditions.checkNotNull(enumConstants);
+    this.enumClass = enumClass;
     this.counters = new long[enumConstants.length];
   }
   
@@ -69,6 +68,13 @@ public final void set(final E e, final long value) {
     counters[e.ordinal()] = value;
   }
 
+  /** Set this counters to that counters. */
+  public final void set(final EnumCounters<E> that) {
+    for(int i = 0; i < counters.length; i++) {
+      this.counters[i] = that.counters[i];
+    }
+  }
+
   /** Add the given value to counter e. */
   public final void add(final E e, final long value) {
     counters[e.ordinal()] += value;
@@ -86,15 +92,33 @@ public final void subtract(final E e, final long value) {
     counters[e.ordinal()] -= value;
   }
 
-  /** Subtract that counters from this counters. */
+  /** Subtract this counters from that counters. */
   public final void subtract(final EnumCounters<E> that) {
     for(int i = 0; i < counters.length; i++) {
       this.counters[i] -= that.counters[i];
     }
   }
 
+  @Override
+  public boolean equals(Object obj) {
+    if (obj == this) {
+      return true;
+    } else if (obj == null || !(obj instanceof EnumCounters)) {
+      return false;
+    }
+    final EnumCounters<?> that = (EnumCounters<?>)obj;
+    return this.enumClass == that.enumClass
+        && Arrays.equals(this.counters, that.counters);
+  }
+
+  @Override
+  public int hashCode() {
+    return Arrays.hashCode(counters);
+  }
+
   @Override
   public String toString() {
+    final E[] enumConstants = enumClass.getEnumConstants();
     final StringBuilder b = new StringBuilder();
     for(int i = 0; i < counters.length; i++) {
       final String name = enumConstants[i].name();