diff --git a/xstream-distribution/src/content/changes.html b/xstream-distribution/src/content/changes.html
index 1e0a3fe4d..24759f883 100644
--- a/xstream-distribution/src/content/changes.html
+++ b/xstream-distribution/src/content/changes.html
@@ -111,6 +111,7 @@ <h1 id="upcoming-1.4.x">Upcoming 1.4.x maintenance release</h1>
 	<h2>Major changes</h2>
 
 	<ul>
+		<li>GHPR:#350: Optimize memory allocation (by Vladislav Rassokhin of JetBrains).</li>
 		<li>Add a converter for the WeakHashMap which does not write any elements of the map.  Avoids also access to the
 		ReentrantLock contained in the WeakHashMap since Java 19.</li>
 	</ul>
@@ -122,7 +123,7 @@ <h2>Minor changes</h2>
 		<li>GHPR:#331, GHI:#326: Fix handling of empty java.util.concurrent.atomic.AtomicReference (by Alex Blekhman of Atlassian).</li>
 		<li>GHPR:#334: Fix remaining buffer size calculation in QuickWriter (by Higuchi Yuta).</li>
 		<li>GHI:#342: Optimize internal handling of children in DomReader avoiding O(n²) access times for siblings (by Shiang-Yun Yang).</li>
-		<li>GHPR:#349: Fix support of lambda objects for Java 21 and above (Tobias Gierke).</li>
+		<li>GHPR:#349: Fix support of lambda objects for Java 21 and above (by Tobias Gierke).</li>
 		<li>GHI:#359: Add KEYS file with public keys to verify signed artifacts.</li>
 		<li>Detect input manipulation in c.t.x.io.binary.BinaryStreamReader.</li>
 	</ul>
diff --git a/xstream-distribution/src/content/team.html b/xstream-distribution/src/content/team.html
index d1cefbce8..06a556c90 100644
--- a/xstream-distribution/src/content/team.html
+++ b/xstream-distribution/src/content/team.html
@@ -1,7 +1,7 @@
 <html>
 <!--
  Copyright (C) 2005, 2006 Joe Walnes.
- Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2013, 2014, 2015, 2016, 2017, 2019, 2020, 2021, 2022 XStream committers.
+ Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2013, 2014, 2015, 2016, 2017, 2019, 2020, 2021, 2022, 2024 XStream committers.
  All rights reserved.
  
  The software in this package is published under the terms of the BSD
@@ -132,6 +132,7 @@ <h2 id="contributors">Contributors</h2>
       <li>Chris Hegarty of Oracle</li>
       <li>Emanuel Alves</li>
       <li>Basil Crow</li>
+	  <li>Vladislav Rassokhin of JetBrains</li>
     </ul>
 
     <p>Please direct all correspondence about XStream to the <a href="mailing-lists.html">mailing list</a>
diff --git a/xstream/src/java/com/thoughtworks/xstream/converters/extended/ToAttributedValueConverter.java b/xstream/src/java/com/thoughtworks/xstream/converters/extended/ToAttributedValueConverter.java
index 02f617550..01accbed4 100644
--- a/xstream/src/java/com/thoughtworks/xstream/converters/extended/ToAttributedValueConverter.java
+++ b/xstream/src/java/com/thoughtworks/xstream/converters/extended/ToAttributedValueConverter.java
@@ -1,11 +1,11 @@
 /*
- * Copyright (C) 2011, 2013, 2014, 2015, 2016 XStream Committers.
+ * Copyright (C) 2011, 2013, 2014, 2015, 2016, 2024 XStream Committers.
  * All rights reserved.
  *
  * The software in this package is published under the terms of the BSD
  * style license a copy of which has been included with this distribution in
  * the LICENSE.txt file.
- * 
+ *
  * Created on 30. July 2011 by Joerg Schaible
  */
 
@@ -28,8 +28,8 @@
 import com.thoughtworks.xstream.converters.UnmarshallingContext;
 import com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.DuplicateFieldException;
 import com.thoughtworks.xstream.converters.reflection.ReflectionProvider;
-import com.thoughtworks.xstream.core.util.FastField;
 import com.thoughtworks.xstream.core.util.HierarchicalStreams;
+import com.thoughtworks.xstream.core.util.MemberDictionary;
 import com.thoughtworks.xstream.core.util.Primitives;
 import com.thoughtworks.xstream.io.HierarchicalStreamReader;
 import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
@@ -45,7 +45,7 @@
  * field name itself. Therefore it is possible to define an inherited field as value. It is also possible to provide no
  * value field at all, so that all fields are written as attributes.
  * </p>
- * 
+ *
  * @author J&ouml;rg Schaible
  * @since 1.4
  */
@@ -59,10 +59,9 @@ public class ToAttributedValueConverter implements Converter {
     private final Field valueField;
 
     /**
-     * Creates a new ToAttributedValueConverter instance.
-     * 
-     * All field elements will be attributes, the element itself will have no value.
-     * 
+     * Creates a new ToAttributedValueConverter instance. All field elements will be attributes, the element itself will
+     * have no value.
+     *
      * @param type the type that is handled by this converter instance
      * @param mapper the mapper in use
      * @param reflectionProvider the reflection provider in use
@@ -77,7 +76,7 @@ public ToAttributedValueConverter(
 
     /**
      * Creates a new ToAttributedValueConverter instance.
-     * 
+     *
      * @param type the type that is handled by this converter instance
      * @param mapper the mapper in use
      * @param reflectionProvider the reflection provider in use
@@ -92,7 +91,7 @@ public ToAttributedValueConverter(
 
     /**
      * Creates a new ToAttributedValueConverter instance.
-     * 
+     *
      * @param type the type that is handled by this converter instance
      * @param mapper the mapper in use
      * @param reflectionProvider the reflection provider in use
@@ -140,17 +139,17 @@ public void marshal(final Object source, final HierarchicalStreamWriter writer,
         final Class<?>[] definingType = new Class[1];
         reflectionProvider.visitSerializableFields(source, new ReflectionProvider.Visitor() {
             @Override
-            public void visit(final String fieldName, final Class<?> type, final Class<?> definedIn, final Object value) {
+            public void visit(final String fieldName, final Class<?> type, final Class<?> definedIn,
+                    final Object value) {
                 if (!mapper.shouldSerializeMember(definedIn, fieldName)) {
                     return;
                 }
 
-                final FastField field = new FastField(definedIn, fieldName);
                 final String alias = mapper.serializedMember(definedIn, fieldName);
                 if (!defaultFieldDefinition.containsKey(alias)) {
                     final Class<?> lookupType = sourceType;
                     defaultFieldDefinition.put(alias, reflectionProvider.getField(lookupType, fieldName));
-                } else if (!fieldIsEqual(field)) {
+                } else if (!fieldIsEqual(definedIn, fieldName)) {
                     final ConversionException exception = new ConversionException(
                         "Cannot write attribute twice for object");
                     exception.add("alias", alias);
@@ -158,15 +157,15 @@ public void visit(final String fieldName, final Class<?> type, final Class<?> de
                     throw exception;
                 }
 
-                ConverterMatcher converter = Enum.class.isAssignableFrom(type) ? (ConverterMatcher)enumMapper
-                    .getConverterFromItemType(null, type, null) : (ConverterMatcher)mapper.getLocalConverter(definedIn,
-                    fieldName);
+                ConverterMatcher converter = Enum.class.isAssignableFrom(type)
+                    ? (ConverterMatcher)enumMapper.getConverterFromItemType(null, type, null)
+                    : (ConverterMatcher)mapper.getLocalConverter(definedIn, fieldName);
                 if (converter == null) {
                     converter = lookup.lookupConverterForType(type);
                 }
 
                 if (value != null) {
-                    final boolean isValueField = valueField != null && fieldIsEqual(field);
+                    final boolean isValueField = valueField != null && fieldIsEqual(definedIn, fieldName);
                     if (isValueField) {
                         definingType[0] = definedIn;
                         fieldType[0] = type;
@@ -222,7 +221,7 @@ public Object unmarshal(final HierarchicalStreamReader reader, final Unmarshalli
         final Object result = reflectionProvider.newInstance(context.getRequiredType());
         final Class<?> resultType = result.getClass();
 
-        final Set<FastField> seenFields = new HashSet<>();
+        final MemberDictionary seenFields = new MemberDictionary();
         final Iterator<String> it = reader.getAttributeNames();
 
         final Set<String> systemAttributes = new HashSet<>();
@@ -244,9 +243,9 @@ public Object unmarshal(final HierarchicalStreamReader reader, final Unmarshalli
 
                 Class<?> type = field.getType();
                 final Class<?> declaringClass = field.getDeclaringClass();
-                ConverterMatcher converter = Enum.class.isAssignableFrom(type) ? (ConverterMatcher)enumMapper
-                    .getConverterFromItemType(null, type, null) : (ConverterMatcher)mapper.getLocalConverter(
-                    declaringClass, fieldName);
+                ConverterMatcher converter = Enum.class.isAssignableFrom(type)
+                    ? (ConverterMatcher)enumMapper.getConverterFromItemType(null, type, null)
+                    : (ConverterMatcher)mapper.getLocalConverter(declaringClass, fieldName);
                 if (converter == null) {
                     converter = lookup.lookupConverterForType(type);
                 }
@@ -273,7 +272,7 @@ public Object unmarshal(final HierarchicalStreamReader reader, final Unmarshalli
                     }
 
                     reflectionProvider.writeField(result, fieldName, value, declaringClass);
-                    if (!seenFields.add(new FastField(declaringClass, fieldName))) {
+                    if (!seenFields.add(declaringClass, fieldName)) {
                         throw new DuplicateFieldException(fieldName + " [" + declaringClass.getName() + "]");
                     }
                 }
@@ -317,15 +316,15 @@ public Object unmarshal(final HierarchicalStreamReader reader, final Unmarshalli
             }
 
             reflectionProvider.writeField(result, fieldName, value, classDefiningField);
-            if (!seenFields.add(new FastField(classDefiningField, fieldName))) {
+            if (!seenFields.add(classDefiningField, fieldName)) {
                 throw new DuplicateFieldException(fieldName + " [" + classDefiningField.getName() + "]");
             }
         }
         return result;
     }
 
-    private boolean fieldIsEqual(final FastField field) {
-        return valueField.getName().equals(field.getName())
-            && valueField.getDeclaringClass().getName().equals(field.getDeclaringClass());
+    private boolean fieldIsEqual(final Class<?> definedIn, final String name) {
+        return valueField.getName().equals(name)
+            && valueField.getDeclaringClass().getName().equals(definedIn.getName());
     }
 }
diff --git a/xstream/src/java/com/thoughtworks/xstream/converters/javabean/JavaBeanConverter.java b/xstream/src/java/com/thoughtworks/xstream/converters/javabean/JavaBeanConverter.java
index 5c972db1a..57c0aee4d 100644
--- a/xstream/src/java/com/thoughtworks/xstream/converters/javabean/JavaBeanConverter.java
+++ b/xstream/src/java/com/thoughtworks/xstream/converters/javabean/JavaBeanConverter.java
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2005 Joe Walnes.
- * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2018 XStream Committers.
+ * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2018, 2024 XStream Committers.
  * All rights reserved.
  *
  * The software in this package is published under the terms of the BSD
@@ -11,15 +11,12 @@
  */
 package com.thoughtworks.xstream.converters.javabean;
 
-import java.util.HashSet;
-import java.util.Set;
-
 import com.thoughtworks.xstream.converters.ConversionException;
 import com.thoughtworks.xstream.converters.Converter;
 import com.thoughtworks.xstream.converters.MarshallingContext;
 import com.thoughtworks.xstream.converters.UnmarshallingContext;
 import com.thoughtworks.xstream.converters.reflection.MissingFieldException;
-import com.thoughtworks.xstream.core.util.FastField;
+import com.thoughtworks.xstream.core.util.MemberDictionary;
 import com.thoughtworks.xstream.io.HierarchicalStreamReader;
 import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
 import com.thoughtworks.xstream.mapper.Mapper;
@@ -107,16 +104,7 @@ private void writeNullField(final String propertyName) {
     @Override
     public Object unmarshal(final HierarchicalStreamReader reader, final UnmarshallingContext context) {
         final Object result = instantiateNewInstance(context);
-        @SuppressWarnings("serial")
-        final Set<FastField> seenProperties = new HashSet<FastField>() {
-            @Override
-            public boolean add(final FastField e) {
-                if (!super.add(e)) {
-                    throw new DuplicatePropertyException(e.getName());
-                }
-                return true;
-            }
-        };
+        final MemberDictionary seenProperties = new MemberDictionary();
 
         final Class<?> resultType = result.getClass();
         while (reader.hasMoreChildren()) {
@@ -131,7 +119,9 @@ public boolean add(final FastField e) {
                     final Class<?> type = determineType(reader, result, propertyName);
                     final Object value = context.convertAnother(result, type);
                     beanProvider.writeProperty(result, propertyName, value);
-                    seenProperties.add(new FastField(resultType, propertyName));
+                    if (!seenProperties.add(resultType, propertyName)) {
+                        throw new DuplicatePropertyException(propertyName);
+                    }
                 } else if (!mapper.isIgnoredElement(propertyName)) {
                     throw new MissingFieldException(resultType.getName(), propertyName);
                 }
diff --git a/xstream/src/java/com/thoughtworks/xstream/converters/reflection/AbstractReflectionConverter.java b/xstream/src/java/com/thoughtworks/xstream/converters/reflection/AbstractReflectionConverter.java
index 10467dda2..5f2e27349 100644
--- a/xstream/src/java/com/thoughtworks/xstream/converters/reflection/AbstractReflectionConverter.java
+++ b/xstream/src/java/com/thoughtworks/xstream/converters/reflection/AbstractReflectionConverter.java
@@ -1,8 +1,8 @@
 /*
  * Copyright (C) 2004, 2005, 2006 Joe Walnes.
- * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2018, 2022 XStream Committers.
+ * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2018, 2022, 2024 XStream Committers.
  * All rights reserved.
- *
+         *
  * The software in this package is published under the terms of the BSD
  * style license a copy of which has been included with this distribution in
  * the LICENSE.txt file.
@@ -33,9 +33,9 @@
 import com.thoughtworks.xstream.core.Caching;
 import com.thoughtworks.xstream.core.ReferencingMarshallingContext;
 import com.thoughtworks.xstream.core.util.ArrayIterator;
-import com.thoughtworks.xstream.core.util.FastField;
 import com.thoughtworks.xstream.core.util.Fields;
 import com.thoughtworks.xstream.core.util.HierarchicalStreams;
+import com.thoughtworks.xstream.core.util.MemberDictionary;
 import com.thoughtworks.xstream.core.util.Primitives;
 import com.thoughtworks.xstream.core.util.SerializationMembers;
 import com.thoughtworks.xstream.io.HierarchicalStreamReader;
@@ -190,8 +190,7 @@ public void writeItem(final Object item) {
             }
         };
 
-        final Map<String, Set<Mapper.ImplicitCollectionMapping>> hiddenMappers =
-                new HashMap<>();
+        final Map<String, Set<Mapper.ImplicitCollectionMapping>> hiddenMappers = new HashMap<>();
         for (final FieldInfo info : fields) {
             if (info.value != null) {
                 final boolean isCollection = info.value instanceof Collection;
@@ -279,16 +278,7 @@ public Object unmarshal(final HierarchicalStreamReader reader, final Unmarshalli
     public Object doUnmarshal(final Object result, final HierarchicalStreamReader reader,
             final UnmarshallingContext context) {
         final Class<?> resultType = result.getClass();
-        @SuppressWarnings("serial")
-        final Set<FastField> seenFields = new HashSet<FastField>() {
-            @Override
-            public boolean add(final FastField e) {
-                if (!super.add(e)) {
-                    throw new DuplicateFieldException(e.getName());
-                }
-                return true;
-            }
-        };
+        final MemberDictionary seenFields = new MemberDictionary();
 
         // process attributes before recursing into child elements.
         final Iterator<String> it = reader.getAttributeNames();
@@ -318,7 +308,9 @@ public boolean add(final FastField e) {
                         exception.add("target-type", type.getName());
                         throw exception;
                     }
-                    seenFields.add(new FastField(classDefiningField, attrName));
+                    if (!seenFields.add(classDefiningField, attrName)) {
+                        throw new DuplicateFieldException(attrName);
+                    }
                     reflectionProvider.writeField(result, attrName, value, classDefiningField);
                 }
             }
@@ -445,13 +437,18 @@ public boolean add(final FastField e) {
 
             if (field != null) {
                 reflectionProvider.writeField(result, fieldName, value, field.getDeclaringClass());
-                seenFields.add(new FastField(field.getDeclaringClass(), fieldName));
+                if (!seenFields.add(field.getDeclaringClass(), fieldName)) {
+                    throw new DuplicateFieldException(fieldName);
+                }
             } else if (type != null) {
                 if (implicitFieldName == null) {
                     // look for implicit field
                     implicitFieldName = mapper.getFieldNameForItemTypeAndName(fieldDeclaringClass, value != null
                         ? value.getClass()
                         : Mapper.Null.class, originalNodeName);
+                    implicitFieldName = mapper.getFieldNameForItemTypeAndName(fieldDeclaringClass, value != null
+                        ? value.getClass()
+                        : Mapper.Null.class, originalNodeName);
                 }
                 if (implicitCollectionsForCurrentObject == null) {
                     implicitCollectionsForCurrentObject = new HashMap<>();
@@ -625,10 +622,7 @@ public boolean equals(final Object obj) {
             if (this == obj) {
                 return true;
             }
-            if (obj == null) {
-                return false;
-            }
-            if (getClass() != obj.getClass()) {
+            if ((obj == null) || (getClass() != obj.getClass())) {
                 return false;
             }
             final FieldLocation other = (FieldLocation)obj;
diff --git a/xstream/src/java/com/thoughtworks/xstream/converters/reflection/SerializableConverter.java b/xstream/src/java/com/thoughtworks/xstream/converters/reflection/SerializableConverter.java
index 81a4e35b7..66a6f6d69 100644
--- a/xstream/src/java/com/thoughtworks/xstream/converters/reflection/SerializableConverter.java
+++ b/xstream/src/java/com/thoughtworks/xstream/converters/reflection/SerializableConverter.java
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2004, 2005, 2006 Joe Walnes.
- * Copyright (C) 2006, 2007, 2008, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2018 XStream Committers.
+ * Copyright (C) 2006, 2007, 2008, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2018, 2024 XStream Committers.
  * All rights reserved.
  *
  * The software in this package is published under the terms of the BSD
@@ -396,7 +396,7 @@ public Map<String, Object> readFieldsFromStream() {
 
             @Override
             public void defaultReadObject() {
-                if (serializationMembers.getSerializablePersistentFields(currentType[0]) != null) {
+                if (serializationMembers.hasSerializablePersistentFields(currentType[0])) {
                     readFieldsFromStream();
                     return;
                 }
diff --git a/xstream/src/java/com/thoughtworks/xstream/core/util/FastField.java b/xstream/src/java/com/thoughtworks/xstream/core/util/FastField.java
deleted file mode 100644
index 25810f10f..000000000
--- a/xstream/src/java/com/thoughtworks/xstream/core/util/FastField.java
+++ /dev/null
@@ -1,63 +0,0 @@
-/*
- * Copyright (C) 2008, 2010, 2014 XStream Committers.
- * All rights reserved.
- *
- * The software in this package is published under the terms of the BSD
- * style license a copy of which has been included with this distribution in
- * the LICENSE.txt file.
- *
- * Created on 13. October 2008 by Joerg Schaible
- */
-package com.thoughtworks.xstream.core.util;
-
-public final class FastField {
-    private final String name;
-    private final String declaringClass;
-
-    public FastField(final String definedIn, final String name) {
-        this.name = name;
-        declaringClass = definedIn;
-    }
-
-    public FastField(final Class<?> definedIn, final String name) {
-        this(definedIn == null ? null : definedIn.getName(), name);
-    }
-
-    public String getName() {
-        return name;
-    }
-
-    public String getDeclaringClass() {
-        return declaringClass;
-    }
-
-    @Override
-    public boolean equals(final Object obj) {
-        if (this == obj) {
-            return true;
-        }
-        if (obj == null) {
-            return false;
-        }
-        if (obj instanceof FastField) {
-            final FastField field = (FastField)obj;
-            if (declaringClass == null && field.declaringClass != null
-                    || declaringClass != null && field.declaringClass == null) {
-                return false;
-            }
-            return name.equals(field.getName())
-                    && (declaringClass == null || declaringClass.equals(field.getDeclaringClass()));
-        }
-        return false;
-    }
-
-    @Override
-    public int hashCode() {
-        return name.hashCode() ^ (declaringClass == null ? 0 : declaringClass.hashCode());
-    }
-
-    @Override
-    public String toString() {
-        return (declaringClass == null ? "" : declaringClass + ".") + name;
-    }
-}
\ No newline at end of file
diff --git a/xstream/src/java/com/thoughtworks/xstream/core/util/MemberDictionary.java b/xstream/src/java/com/thoughtworks/xstream/core/util/MemberDictionary.java
new file mode 100644
index 000000000..065dbc6cd
--- /dev/null
+++ b/xstream/src/java/com/thoughtworks/xstream/core/util/MemberDictionary.java
@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2024 XStream Committers.
+ * All rights reserved.
+ *
+ * The software in this package is published under the terms of the BSD
+ * style license a copy of which has been included with this distribution in
+ * the LICENSE.txt file.
+ *
+ * Created on 21. October 2024 by Joerg Schaible
+ */
+package com.thoughtworks.xstream.core.util;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+
+/**
+ * A dictionary for member information of types.
+ *
+ * @author J&ouml;rg Schaible
+ * @since upcoming
+ */
+public class MemberDictionary {
+
+    private final Map<String, Set<String>> types;
+
+    /**
+     * Constructs an instance.
+     *
+     * @since upcoming
+     */
+    public MemberDictionary() {
+        types = new HashMap<>();
+    }
+
+    /**
+     * Add the member of the type into the dictionary.
+     *
+     * @param definedIn the type owning the member or null
+     * @param member the member name
+     * @return true if the member has been added to the dictionary
+     * @since upcoming
+     */
+    public boolean add(final Class<?> definedIn, final String member) {
+        final String className = definedIn == null ? null : definedIn.getName();
+        Set<String> members = types.get(className);
+        if (members == null) {
+            members = new HashSet<>();
+            types.put(className, members);
+        }
+        return members.add(member);
+    }
+
+    /**
+     * Checks the existence of the member of a type in the dictionary.
+     *
+     * @param definedIn the type owning the member or null
+     * @param member the member name
+     * @return true if the member is in the dictionary
+     * @since upcoming
+     */
+    public boolean contains(final Class<?> definedIn, final String member) {
+        final String className = definedIn == null ? null : definedIn.getName();
+        final Set<String> members = types.get(className);
+        return members != null && members.contains(member);
+    }
+}
diff --git a/xstream/src/java/com/thoughtworks/xstream/core/util/MemberStore.java b/xstream/src/java/com/thoughtworks/xstream/core/util/MemberStore.java
new file mode 100644
index 000000000..61fb7cca3
--- /dev/null
+++ b/xstream/src/java/com/thoughtworks/xstream/core/util/MemberStore.java
@@ -0,0 +1,98 @@
+/*
+ * Copyright (C) 2024 XStream Committers.
+ * All rights reserved.
+ *
+ * The software in this package is published under the terms of the BSD
+ * style license a copy of which has been included with this distribution in
+ * the LICENSE.txt file.
+ *
+ * Created on 21. October 2024 by Joerg Schaible
+ */
+package com.thoughtworks.xstream.core.util;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+
+
+/**
+ * A store for member information of types.
+ *
+ * @author J&ouml;rg Schaible
+ * @since upcoming
+ */
+public class MemberStore<T> {
+
+    private final Map<String, Map<String, T>> types;
+    private final boolean synced;
+
+    /**
+     * Creates a new instance of a MemberStore.
+     *
+     * @since upcoming
+     */
+    public static <T> MemberStore<T> newInstance() {
+        return new MemberStore<>(false);
+    }
+
+    /**
+     * Creates a new synchronized instance of a MemberStore.
+     *
+     * @since upcoming
+     */
+    public static <T> MemberStore<T> newSynchronizedInstance() {
+        return new MemberStore<>(true);
+    }
+
+    private MemberStore(final boolean synced) {
+        this.synced = synced;
+        types = synced ? new ConcurrentHashMap<>() : new HashMap<>();
+    }
+
+    /**
+     * Put an element for a the member of the type into the store.
+     *
+     * @param definedIn the type owning the member or null
+     * @param member the member name
+     * @param value the value to store
+     * @return the old stored value for the member or null
+     * @since upcoming
+     */
+    public Object put(final Class<?> definedIn, final String member, final T value) {
+        final String className = definedIn == null ? null : definedIn.getName();
+        Map<String, T> store = types.get(className);
+        if (store == null) {
+            store = synced ? new ConcurrentHashMap<>() : new HashMap<>();
+            types.put(className, store);
+        }
+        return store.put(member, value);
+    }
+
+    /**
+     * Get the value for a type's member in the store.
+     *
+     * @param definedIn the type owning the member or null
+     * @param member the member name
+     * @return the stored value for the member or null
+     * @since upcoming
+     */
+    public T get(final Class<?> definedIn, final String member) {
+        final String className = definedIn == null ? null : definedIn.getName();
+        final Map<String, T> store = types.get(className);
+        if (store != null) {
+            return store.get(member);
+        }
+        return null;
+    }
+
+    /**
+     * Get the set of types in the store.
+     *
+     * @return the set of type names
+     * @since upcoming
+     */
+    public Set<String> keySet() {
+        return types.keySet();
+    }
+}
diff --git a/xstream/src/java/com/thoughtworks/xstream/core/util/SerializationMembers.java b/xstream/src/java/com/thoughtworks/xstream/core/util/SerializationMembers.java
index ce7c3fec7..5a425589f 100644
--- a/xstream/src/java/com/thoughtworks/xstream/core/util/SerializationMembers.java
+++ b/xstream/src/java/com/thoughtworks/xstream/core/util/SerializationMembers.java
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2004, 2005 Joe Walnes.
- * Copyright (C) 2006, 2007, 2008, 2010, 2011, 2014, 2015, 2016, 2017, 2021 XStream Committers.
+ * Copyright (C) 2006, 2007, 2008, 2010, 2011, 2014, 2015, 2016, 2017, 2021, 2024 XStream Committers.
  * All rights reserved.
  *
  * The software in this package is published under the terms of the BSD
@@ -19,9 +19,6 @@
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
 import java.util.Arrays;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 
@@ -39,26 +36,26 @@
  */
 public class SerializationMembers implements Caching {
 
-    private static final Method NO_METHOD = new Object() {
+    private static final class NO_METHOD_MARKER {
         @SuppressWarnings("unused")
         private void noMethod() {
         }
-    }.getClass().getDeclaredMethods()[0];
-    private static final Map<String, ObjectStreamField> NO_FIELDS = Collections.emptyMap();
+    }
+
+    private static final Method NO_METHOD = NO_METHOD_MARKER.class.getDeclaredMethods()[0];
+    private static final ObjectStreamField[] NO_FIELDS = new ObjectStreamField[0];
     private static final int PERSISTENT_FIELDS_MODIFIER = Modifier.PRIVATE | Modifier.STATIC | Modifier.FINAL;
-    private static final FastField[] OBJECT_TYPE_FIELDS = {
-        new FastField(Object.class, "readResolve"), new FastField(Object.class, "writeReplace"), new FastField(
-            Object.class, "readObject"), new FastField(Object.class, "writeObject")};
-    private final ConcurrentMap<FastField, Method> declaredCache = new ConcurrentHashMap<>();
-    private final ConcurrentMap<FastField, Method> resRepCache = new ConcurrentHashMap<>();
-    private final ConcurrentMap<String, Map<String, ObjectStreamField>> fieldCache = new ConcurrentHashMap<>();
+    private static final String[] OBJECT_TYPE_FIELDS = {"readResolve", "writeReplace", "readObject", "writeObject"};
+    private final MemberStore<Method> declaredCache = MemberStore.newSynchronizedInstance();
+    private final MemberStore<Method> resRepCache = MemberStore.newSynchronizedInstance();
+    private final ConcurrentMap<String, ObjectStreamField[]> fieldCache = new ConcurrentHashMap<>();
 
     {
-        for (final FastField element : OBJECT_TYPE_FIELDS) {
-            declaredCache.put(element, NO_METHOD);
+        for (final String element : OBJECT_TYPE_FIELDS) {
+            declaredCache.put(Object.class, element, NO_METHOD);
         }
-        for (final FastField element : Arrays.copyOf(OBJECT_TYPE_FIELDS, 2)) {
-            resRepCache.put(element, NO_METHOD);
+        for (int i = 0; i < 2; ++i) {
+            resRepCache.put(Object.class, OBJECT_TYPE_FIELDS[i], NO_METHOD);
         }
     }
 
@@ -150,9 +147,10 @@ public void callWriteObject(final Class<?> type, final Object instance, final Ob
         } catch (final IllegalAccessException e) {
             ex = new ObjectAccessException("Cannot access method", e);
         } catch (final InvocationTargetException e) {
-            Throwable cause = e.getTargetException();
-            if (cause instanceof ConversionException)
-                    throw (ConversionException)cause;
+            final Throwable cause = e.getTargetException();
+            if (cause instanceof ConversionException) {
+                throw (ConversionException)cause;
+            }
             ex = new ConversionException("Failed calling method", e.getTargetException());
         }
         if (ex != null) {
@@ -171,8 +169,7 @@ private Method getMethod(final Class<?> type, final String name, final Class<?>.
         if (type == null) {
             return null;
         }
-        final FastField method = new FastField(type, name);
-        Method result = declaredCache.get(method);
+        Method result = declaredCache.get(type, name);
 
         if (result == null) {
             try {
@@ -183,14 +180,13 @@ private Method getMethod(final Class<?> type, final String name, final Class<?>.
             } catch (final NoSuchMethodException e) {
                 result = getMethod(type.getSuperclass(), name, parameterTypes);
             }
-            declaredCache.put(method, result);
+            declaredCache.put(type, name, result);
         }
         return result;
     }
 
     private Method getRRMethod(final Class<?> type, final String name) {
-        final FastField method = new FastField(type, name);
-        Method result = resRepCache.get(method);
+        Method result = resRepCache.get(type, name);
         if (result == null) {
             result = getMethod(type, name, true);
             if (result != null && result.getDeclaringClass() != type) {
@@ -203,29 +199,23 @@ private Method getRRMethod(final Class<?> type, final String name) {
             } else if (result == null) {
                 result = NO_METHOD;
             }
-            resRepCache.putIfAbsent(method, result);
+            resRepCache.put(type, name, result);
         }
         return result == NO_METHOD ? null : result;
     }
 
-    public Map<String, ObjectStreamField> getSerializablePersistentFields(final Class<?> type) {
+    public boolean hasSerializablePersistentFields(final Class<?> type) {
         if (type == null) {
-            return null;
+            return false;
         }
-        Map<String, ObjectStreamField> result = fieldCache.get(type.getName());
+        ObjectStreamField[] result = fieldCache.get(type.getName());
         if (result == null) {
             ErrorWritingException ex = null;
             try {
                 final Field field = type.getDeclaredField("serialPersistentFields");
                 if ((field.getModifiers() & PERSISTENT_FIELDS_MODIFIER) == PERSISTENT_FIELDS_MODIFIER) {
                     field.setAccessible(true);
-                    final ObjectStreamField[] fields = (ObjectStreamField[])field.get(null);
-                    if (fields != null) {
-                        result = new HashMap<>();
-                        for (final ObjectStreamField f : fields) {
-                            result.put(f.getName(), f);
-                        }
-                    }
+                    result = (ObjectStreamField[])field.get(null);
                 }
             } catch (final NoSuchFieldException e) {
             } catch (final IllegalAccessException e) {
@@ -240,14 +230,14 @@ public Map<String, ObjectStreamField> getSerializablePersistentFields(final Clas
             if (result == null) {
                 result = NO_FIELDS;
             }
-            fieldCache.putIfAbsent(type.getName(), result);
+            fieldCache.put(type.getName(), result);
         }
-        return result == NO_FIELDS ? null : result;
+        return result != NO_FIELDS;
     }
 
     @Override
     public void flushCache() {
-        declaredCache.keySet().retainAll(Arrays.asList(OBJECT_TYPE_FIELDS));
-        resRepCache.keySet().retainAll(Arrays.asList(OBJECT_TYPE_FIELDS));
+        declaredCache.keySet().retainAll(Arrays.asList(Object.class.getName()));
+        resRepCache.keySet().retainAll(Arrays.asList(Object.class.getName()));
     }
 }
diff --git a/xstream/src/java/com/thoughtworks/xstream/mapper/ElementIgnoringMapper.java b/xstream/src/java/com/thoughtworks/xstream/mapper/ElementIgnoringMapper.java
index 310baa529..9864ee29c 100644
--- a/xstream/src/java/com/thoughtworks/xstream/mapper/ElementIgnoringMapper.java
+++ b/xstream/src/java/com/thoughtworks/xstream/mapper/ElementIgnoringMapper.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2013, 2016 XStream Committers.
+ * Copyright (C) 2013, 2016, 2024 XStream Committers.
  * All rights reserved.
  *
  * The software in this package is published under the terms of the BSD
@@ -10,12 +10,11 @@
  */
 package com.thoughtworks.xstream.mapper;
 
-import java.util.HashSet;
-import java.util.LinkedHashSet;
-import java.util.Set;
+import java.util.LinkedHashMap;
+import java.util.Map;
 import java.util.regex.Pattern;
 
-import com.thoughtworks.xstream.core.util.FastField;
+import com.thoughtworks.xstream.core.util.MemberDictionary;
 
 
 /**
@@ -25,24 +24,24 @@
  */
 public class ElementIgnoringMapper extends MapperWrapper {
 
-    protected final Set<Pattern> unknownElementsToIgnore = new LinkedHashSet<>();
-    protected final Set<FastField> fieldsToOmit = new HashSet<>();
+    protected final Map<String, Pattern> unknownElementsToIgnore = new LinkedHashMap<>();
+    protected final MemberDictionary fieldsToOmit = new MemberDictionary();
 
     public ElementIgnoringMapper(final Mapper wrapped) {
         super(wrapped);
     }
 
     public void addElementsToIgnore(final Pattern pattern) {
-        unknownElementsToIgnore.add(pattern);
+        unknownElementsToIgnore.put(pattern.pattern(), pattern);
     }
 
     public void omitField(final Class<?> definedIn, final String fieldName) {
-        fieldsToOmit.add(key(definedIn, fieldName));
+        fieldsToOmit.add(definedIn, fieldName);
     }
 
     @Override
     public boolean shouldSerializeMember(final Class<?> definedIn, final String fieldName) {
-        if (fieldsToOmit.contains(key(definedIn, fieldName))) {
+        if (fieldsToOmit.contains(definedIn, fieldName)) {
             return false;
         } else if (definedIn == Object.class && isIgnoredElement(fieldName)) {
             return false;
@@ -53,7 +52,7 @@ public boolean shouldSerializeMember(final Class<?> definedIn, final String fiel
     @Override
     public boolean isIgnoredElement(final String name) {
         if (!unknownElementsToIgnore.isEmpty()) {
-            for (final Pattern pattern : unknownElementsToIgnore) {
+            for (final Pattern pattern : unknownElementsToIgnore.values()) {
                 if (pattern.matcher(name).matches()) {
                     return true;
                 }
@@ -61,8 +60,4 @@ public boolean isIgnoredElement(final String name) {
         }
         return super.isIgnoredElement(name);
     }
-
-    private FastField key(final Class<?> type, final String name) {
-        return new FastField(type, name);
-    }
 }
diff --git a/xstream/src/java/com/thoughtworks/xstream/mapper/FieldAliasingMapper.java b/xstream/src/java/com/thoughtworks/xstream/mapper/FieldAliasingMapper.java
index 110f16b68..d4a1c5772 100644
--- a/xstream/src/java/com/thoughtworks/xstream/mapper/FieldAliasingMapper.java
+++ b/xstream/src/java/com/thoughtworks/xstream/mapper/FieldAliasingMapper.java
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2005 Joe Walnes.
- * Copyright (C) 2006, 2007, 2008, 2009, 2013, 2014, 2015, 2016 XStream Committers.
+ * Copyright (C) 2006, 2007, 2008, 2009, 2013, 2014, 2015, 2016, 2024 XStream Committers.
  * All rights reserved.
  *
  * The software in this package is published under the terms of the BSD
@@ -11,11 +11,9 @@
  */
 package com.thoughtworks.xstream.mapper;
 
-import java.util.HashMap;
-import java.util.Map;
 import java.util.regex.Pattern;
 
-import com.thoughtworks.xstream.core.util.FastField;
+import com.thoughtworks.xstream.core.util.MemberStore;
 
 
 /**
@@ -25,8 +23,8 @@
  */
 public class FieldAliasingMapper extends MapperWrapper {
 
-    protected final Map<FastField, String> fieldToAliasMap = new HashMap<>();
-    protected final Map<FastField, String> aliasToFieldMap = new HashMap<>();
+    private final MemberStore<String> fieldToAliasMap = MemberStore.newInstance();
+    private final MemberStore<String> aliasToFieldMap = MemberStore.newInstance();
     private final ElementIgnoringMapper elementIgnoringMapper;
 
     public FieldAliasingMapper(final Mapper wrapped) {
@@ -35,8 +33,8 @@ public FieldAliasingMapper(final Mapper wrapped) {
     }
 
     public void addFieldAlias(final String alias, final Class<?> type, final String fieldName) {
-        fieldToAliasMap.put(key(type, fieldName), alias);
-        aliasToFieldMap.put(key(type, alias), fieldName);
+        fieldToAliasMap.put(type, fieldName, alias);
+        aliasToFieldMap.put(type, alias, fieldName);
     }
 
     /**
@@ -49,10 +47,6 @@ public void addFieldsToIgnore(final Pattern pattern) {
         }
     }
 
-    private FastField key(final Class<?> type, final String name) {
-        return new FastField(type, name);
-    }
-
     /**
      * @deprecated As of 1.4.9 use {@link ElementIgnoringMapper#omitField(Class, String)}.
      */
@@ -83,13 +77,14 @@ public String realMember(final Class<?> type, final String serialized) {
         }
     }
 
-    private String getMember(final Class<?> type, final String name, final Map<FastField, String> map) {
-        String member = null;
-        for (Class<?> declaringType = type; member == null
-            && declaringType != Object.class
-            && declaringType != null; declaringType = declaringType.getSuperclass()) {
-            member = map.get(key(declaringType, name));
+    private String getMember(final Class<?> type, final String name, final MemberStore<String> store) {
+        for (Class<?> declaringType = type; declaringType != Object.class && declaringType != null; declaringType =
+                declaringType.getSuperclass()) {
+            final String member = store.get(declaringType, name);
+            if (member != null) {
+                return member;
+            }
         }
-        return member;
+        return null;
     }
 }
diff --git a/xstream/src/java/com/thoughtworks/xstream/mapper/LocalConversionMapper.java b/xstream/src/java/com/thoughtworks/xstream/mapper/LocalConversionMapper.java
index 456331366..541017362 100644
--- a/xstream/src/java/com/thoughtworks/xstream/mapper/LocalConversionMapper.java
+++ b/xstream/src/java/com/thoughtworks/xstream/mapper/LocalConversionMapper.java
@@ -1,37 +1,34 @@
 /*
- * Copyright (C) 2007, 2008, 2014, 2015 XStream Committers.
+ * Copyright (C) 2007, 2008, 2014, 2015, 2024 XStream Committers.
  * All rights reserved.
  *
  * The software in this package is published under the terms of the BSD
  * style license a copy of which has been included with this distribution in
  * the LICENSE.txt file.
- * 
+ *
  * Created on 06. November 2007 by Joerg Schaible
  */
 package com.thoughtworks.xstream.mapper;
 
-import java.util.HashMap;
-import java.util.Map;
-
 import com.thoughtworks.xstream.converters.Converter;
 import com.thoughtworks.xstream.converters.SingleValueConverter;
-import com.thoughtworks.xstream.core.util.FastField;
+import com.thoughtworks.xstream.core.util.MemberStore;
 
 
 /**
  * A Mapper for locally defined converters for a member field.
- * 
+ *
  * @author J&ouml;rg Schaible
  * @since 1.3
  */
 public class LocalConversionMapper extends MapperWrapper {
 
-    private final Map<FastField, Converter> localConverters = new HashMap<>();
+    private final MemberStore<Converter> localConverters = MemberStore.newInstance();
     private transient AttributeMapper attributeMapper;
 
     /**
      * Constructs a LocalConversionMapper.
-     * 
+     *
      * @param wrapped
      * @since 1.3
      */
@@ -41,12 +38,12 @@ public LocalConversionMapper(final Mapper wrapped) {
     }
 
     public void registerLocalConverter(final Class<?> definedIn, final String fieldName, final Converter converter) {
-        localConverters.put(new FastField(definedIn, fieldName), converter);
+        localConverters.put(definedIn, fieldName, converter);
     }
 
     @Override
     public Converter getLocalConverter(final Class<?> definedIn, final String fieldName) {
-        return localConverters.get(new FastField(definedIn, fieldName));
+        return localConverters.get(definedIn, fieldName);
     }
 
     @Override
