Index: lucene/src/java/org/apache/lucene/util/Constants.java
===================================================================
--- lucene/src/java/org/apache/lucene/util/Constants.java	(revision 1201662)
+++ lucene/src/java/org/apache/lucene/util/Constants.java	(working copy)
@@ -28,13 +28,20 @@
 
   /** The value of <tt>System.getProperty("java.version")<tt>. **/
   public static final String JAVA_VERSION = System.getProperty("java.version");
-  /** True iff this is Java version 1.1. */
+ 
+  /** True iff this is Java version 1.1.
+   * @deprecated This constant is useless since Lucene is on Java 5 */
+  @Deprecated
   public static final boolean JAVA_1_1 = JAVA_VERSION.startsWith("1.1.");
-  /** True iff this is Java version 1.2. */
+  /** True iff this is Java version 1.2.
+   * @deprecated This constant is useless since Lucene is on Java 5 */
+  @Deprecated
   public static final boolean JAVA_1_2 = JAVA_VERSION.startsWith("1.2.");
-  /** True iff this is Java version 1.3. */
+  /** True iff this is Java version 1.3.
+   * @deprecated This constant is useless since Lucene is on Java 5 */
+  @Deprecated
   public static final boolean JAVA_1_3 = JAVA_VERSION.startsWith("1.3.");
- 
+
   /** The value of <tt>System.getProperty("os.name")<tt>. **/
   public static final String OS_NAME = System.getProperty("os.name");
   /** True iff running on Linux. */
@@ -66,6 +73,17 @@
     }
   }
 
+  public static final boolean JRE_IS_MINIMUM_JAVA6;
+  static {
+    boolean v = true;
+    try {
+      String.class.getMethod("isEmpty");
+    } catch (NoSuchMethodException me) {
+      v = false;
+    }
+    JRE_IS_MINIMUM_JAVA6 = v;
+  }
+
   // this method prevents inlining the final version constant in compiled classes,
   // see: http://www.javaworld.com/community/node/3400
   private static String ident(final String s) {
Index: lucene/src/java/org/apache/lucene/util/DoubleBarrelLRUCache.java
===================================================================
--- lucene/src/java/org/apache/lucene/util/DoubleBarrelLRUCache.java	(revision 1201662)
+++ lucene/src/java/org/apache/lucene/util/DoubleBarrelLRUCache.java	(working copy)
@@ -19,7 +19,10 @@
 
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.Collections;
+import java.util.HashMap;
 import java.util.Map;
+import org.apache.lucene.util.Constants;
 
 /**
  * Simple concurrent LRU cache, using a "double barrel"
@@ -58,8 +61,13 @@
   public DoubleBarrelLRUCache(int maxSize) {
     this.maxSize = maxSize;
     countdown = new AtomicInteger(maxSize);
-    cache1 = new ConcurrentHashMap<K,V>();
-    cache2 = new ConcurrentHashMap<K,V>();
+    if (Constants.JRE_IS_MINIMUM_JAVA6) {
+      cache1 = new ConcurrentHashMap<K,V>();
+      cache2 = new ConcurrentHashMap<K,V>();
+    } else {
+      cache1 = Collections.synchronizedMap(new HashMap<K,V>());
+      cache2 = Collections.synchronizedMap(new HashMap<K,V>());
+    }
   }
 
   @SuppressWarnings("unchecked")