src/jdk.jlink/share/classes/jdk/tools/jlink/internal/ImageStringsWriter.java

@@ -1,7 +1,7 @@
  /*
-  * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+  * Copyright (c) 2014, 2025, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this

@@ -31,29 +31,32 @@
  import jdk.internal.jimage.ImageStrings;
  import jdk.internal.jimage.ImageStringsReader;
  
  class ImageStringsWriter implements ImageStrings {
      private static final int NOT_FOUND = -1;
-     static final int EMPTY_OFFSET = 0;
  
      private final HashMap<String, Integer> stringToOffsetMap;
      private final ImageStream stream;
  
      ImageStringsWriter() {
          this.stringToOffsetMap = new HashMap<>();
          this.stream = new ImageStream();
  
-         // Reserve 0 offset for empty string.
-         int offset = addString("");
-         if (offset != 0) {
-             throw new InternalError("Empty string not offset zero");
-         }
+         // Frequently used/special strings for which the offset is useful.
+         // New strings can be reserved after existing strings without having to
+         // change the jimage file version, but any change to existing entries
+         // requires the jimage file version to be increased at the same time.
+         reserveString("", ImageStrings.EMPTY_STRING_OFFSET);
+         reserveString("class", ImageStrings.CLASS_STRING_OFFSET);
+         reserveString("modules", ImageStrings.MODULES_STRING_OFFSET);
+         reserveString("packages", ImageStrings.PACKAGES_STRING_OFFSET);
+     }
  
-         // Reserve 1 offset for frequently used ".class".
-         offset = addString("class");
-         if (offset != 1) {
-             throw new InternalError("'class' string not offset one");
+     private void reserveString(String value, int expectedOffset) {
+         int offset = addString(value);
+         if (offset != expectedOffset) {
+             throw new InternalError("Reserved string \"" + value + "\" not at expected offset " + expectedOffset + "[was " + offset + "]");
          }
      }
  
      private int addString(final String string) {
          int offset = stream.getPosition();