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diff --git a/java/core/src/main/java/com/google/protobuf/FieldInfo.java b/java/core/src/main/java/com/google/protobuf/FieldInfo.java
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+++ b/java/core/src/main/java/com/google/protobuf/FieldInfo.java
@@ -0,0 +1,175 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import static com.google.protobuf.Internal.checkNotNull;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+
+/** Information for a single field in a protobuf message class. */
+@ExperimentalApi
+public final class FieldInfo implements Comparable<FieldInfo> {
+  private final Field field;
+  private final FieldType type;
+  private final int fieldNumber;
+  private final Field presenceField;
+  private final int presenceMask;
+
+  /** Constructs a new descriptor for a field. */
+  public static FieldInfo forField(Field field, int fieldNumber, FieldType fieldType) {
+    return new FieldInfo(field, fieldNumber, fieldType, null, 0);
+  }
+
+  /** Constructor for a field that uses a presence bit field (i.e. proto2 only). */
+  public static FieldInfo forPresenceCheckedField(
+      Field field, int fieldNumber, FieldType fieldType, Field presenceField, int presenceMask) {
+    checkNotNull(presenceField, "presenceField");
+    return new FieldInfo(field, fieldNumber, fieldType, presenceField, presenceMask);
+  }
+
+  private FieldInfo(
+      Field field, int fieldNumber, FieldType type, Field presenceField, int presenceMask) {
+    if (fieldNumber <= 0) {
+      throw new IllegalArgumentException("fieldNumber must be positive: " + fieldNumber);
+    }
+    if (presenceField != null && !isExactlyOneBitSet(presenceMask)) {
+      throw new IllegalArgumentException(
+          "presenceMask must have exactly one bit set: " + presenceMask);
+    }
+    this.field = checkNotNull(field, "field");
+    this.type = checkNotNull(type, "type");
+    this.fieldNumber = fieldNumber;
+    this.presenceField = presenceField;
+    this.presenceMask = presenceMask;
+  }
+
+  /** Gets the subject {@link Field} of this descriptor. */
+  public Field getField() {
+    return field;
+  }
+
+  /** Gets the type information for the field. */
+  public FieldType getType() {
+    return type;
+  }
+
+  /** Gets the field number for the field. */
+  public int getFieldNumber() {
+    return fieldNumber;
+  }
+
+  @Override
+  public int compareTo(FieldInfo o) {
+    return fieldNumber - o.fieldNumber;
+  }
+
+  /**
+   * For list fields, returns the generic argument that represents the type stored in the list. For
+   * non-list fields, returns {@code null}.
+   */
+  public Class<?> getListElementType() {
+    if (!type.isList()) {
+      return null;
+    }
+
+    Type genericType = field.getGenericType();
+    if (!(genericType instanceof ParameterizedType)) {
+      throw new IllegalStateException(
+          "Cannot determine parameterized type for list field " + fieldNumber);
+    }
+
+    Type type = ((ParameterizedType) field.getGenericType()).getActualTypeArguments()[0];
+    return (Class<?>) type;
+  }
+
+  /** Gets the presence bit field. Only valid for unary fields. For lists, returns {@code null}. */
+  public Field getPresenceField() {
+    return presenceField;
+  }
+
+  /**
+   * If {@link #getPresenceField()} is non-{@code null}, returns the mask used to identify the
+   * presence bit for this field in the message.
+   */
+  public int getPresenceMask() {
+    return presenceMask;
+  }
+
+  public static Builder newBuilder() {
+    return new Builder();
+  }
+
+  /** A builder for {@link FieldInfo} instances. */
+  public static final class Builder {
+    private Field field;
+    private FieldType type;
+    private int fieldNumber;
+    private Field presenceField;
+    private int presenceMask;
+
+    private Builder() {}
+
+    public Builder withField(Field field) {
+      this.field = field;
+      return this;
+    }
+
+    public Builder withType(FieldType type) {
+      this.type = type;
+      return this;
+    }
+
+    public Builder withFieldNumber(int fieldNumber) {
+      this.fieldNumber = fieldNumber;
+      return this;
+    }
+
+    public Builder withPresenceField(Field presenceField) {
+      this.presenceField = checkNotNull(presenceField, "presenceField");
+      return this;
+    }
+
+    public Builder withPresenceMask(int presenceMask) {
+      this.presenceMask = presenceMask;
+      return this;
+    }
+
+    public FieldInfo build() {
+      return new FieldInfo(field, fieldNumber, type, presenceField, presenceMask);
+    }
+  }
+
+  private static boolean isExactlyOneBitSet(int value) {
+    return value != 0 && (value & (value - 1)) == 0;
+  }
+}