1 files changed, 72 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/lang3/builder/IDKey.java b/src/main/java/org/apache/commons/lang3/builder/IDKey.java
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index 000000000..64e8fc5b7
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+++ b/src/main/java/org/apache/commons/lang3/builder/IDKey.java
@@ -0,0 +1,72 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.lang3.builder;
+
+// adapted from org.apache.axis.utils.IDKey
+
+/**
+ * Wrap an identity key (System.identityHashCode())
+ * so that an object can only be equal() to itself.
+ *
+ * This is necessary to disambiguate the occasional duplicate
+ * identityHashCodes that can occur.
+ */
+final class IDKey {
+        private final Object value;
+        private final int id;
+
+        /**
+         * Constructor for IDKey
+         * @param value The value
+         */
+        IDKey(final Object value) {
+            // This is the Object hash code
+            this.id = System.identityHashCode(value);
+            // There have been some cases (LANG-459) that return the
+            // same identity hash code for different objects.  So
+            // the value is also added to disambiguate these cases.
+            this.value = value;
+        }
+
+        /**
+         * returns hash code - i.e. the system identity hashcode.
+         * @return the hashcode
+         */
+        @Override
+        public int hashCode() {
+           return id;
+        }
+
+        /**
+         * checks if instances are equal
+         * @param other The other object to compare to
+         * @return if the instances are for the same object
+         */
+        @Override
+        public boolean equals(final Object other) {
+            if (!(other instanceof IDKey)) {
+                return false;
+            }
+            final IDKey idKey = (IDKey) other;
+            if (id != idKey.id) {
+                return false;
+            }
+            // Note that identity equals is used.
+            return value == idKey.value;
+         }
+}