Index: src/test/org/apache/lucene/document/TestDocument.java
===================================================================
--- src/test/org/apache/lucene/document/TestDocument.java	(revision 962932)
+++ src/test/org/apache/lucene/document/TestDocument.java	(working copy)
@@ -1,5 +1,8 @@
 package org.apache.lucene.document;
 
+import java.util.ArrayList;
+import java.util.LinkedList;
+
 import org.apache.lucene.analysis.standard.StandardAnalyzer;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.Term;
@@ -36,7 +39,43 @@
 
   String binaryVal = "this text will be stored as a byte array in the index";
   String binaryVal2 = "this text will be also stored as a byte array in the index";
-  
+
+  /** test the 3 constructor variants */
+  public void testDocumentConstructors() {
+    Document d;
+    d = new Document();
+    assertNotNull(d.fields);
+
+    // unfortunately ArrayList doesn't allow us to validate initialCapacity
+    d = new Document(128);
+    assertNotNull(d.fields);
+
+    ArrayList<Fieldable> fields = new ArrayList<Fieldable>(512);
+    d = new Document(fields);
+    assertSame(fields, d.fields);
+
+    // any kind of list is ok, though perhaps rarely wise
+    LinkedList<Fieldable> linked = new LinkedList<Fieldable>();
+    d = new Document(linked);
+    assertSame(linked, d.fields);
+  }
+
+  /** test the constructor variants exceptions */
+  public void testDocumentConstructorExceptions() {
+    try {
+      new Document(-1);
+      fail("negative capcity should throw an exception");
+    } catch (IllegalArgumentException e) {
+      // expected exception
+    }
+    try {
+      new Document(null);
+      fail("null list should throw an exception");
+    } catch (IllegalArgumentException e) {
+      // expected exception
+    }
+  }
+
   public void testBinaryField()
     throws Exception
   {
Index: src/java/org/apache/lucene/index/FieldsReader.java
===================================================================
--- src/java/org/apache/lucene/index/FieldsReader.java	(revision 962932)
+++ src/java/org/apache/lucene/index/FieldsReader.java	(working copy)
@@ -218,8 +218,8 @@
     long position = indexStream.readLong();
     fieldsStream.seek(position);
 
-    Document doc = new Document();
-    int numFields = fieldsStream.readVInt();
+    final int numFields = fieldsStream.readVInt();
+    final Document doc = new Document((fieldSelector == null && numFields > 10) ? numFields : 10);
     for (int i = 0; i < numFields; i++) {
       int fieldNumber = fieldsStream.readVInt();
       FieldInfo fi = fieldInfos.fieldInfo(fieldNumber);
Index: src/java/org/apache/lucene/document/Document.java
===================================================================
--- src/java/org/apache/lucene/document/Document.java	(revision 962932)
+++ src/java/org/apache/lucene/document/Document.java	(working copy)
@@ -37,13 +37,29 @@
  */
 
 public final class Document implements java.io.Serializable {
-  List<Fieldable> fields = new ArrayList<Fieldable>();
+  final List<Fieldable> fields;
   private float boost = 1.0f;
 
   /** Constructs a new document with no fields. */
-  public Document() {}
+  public Document() {
+    this(new ArrayList<Fieldable>());
+  }
 
+  /** Construct a Document with an initial capacity for fields
+   * @param initialCapacity   initial number of fields in the internal List */
+  public Document(final int initialCapacity) {
+    this(new ArrayList<Fieldable>(initialCapacity));
+  }
 
+  /** Construct a Document with a List of Fieldables
+   * @param fields  a List of Fielables to use. NOT COPIED, so be careful */
+  public Document(final List<Fieldable> fields) {
+    this.fields = fields;
+    if (fields == null) {
+      throw new IllegalArgumentException("fields must be non-null");
+    }
+  }
+
   /** Sets a boost factor for hits on any field of this document.  This value
    * will be multiplied into the score of all hits on this document.
    *