{"record":{"id":"3268048d6c67eb9b","repo":"stanfordnlp/CoreNLP","slug":"error-could-not-find-a-constructor-for-objects-of-326804","errorCode":null,"errorMessage":"Error: could not find a constructor for objects of ${HASH_MAP_CLASS} which takes an existing Map argument.","messagePattern":"Error: could not find a constructor for objects of (.+?) which takes an existing Map argument\\.","errorType":"exception","errorClass":"RuntimeException","httpStatus":null,"severity":"error","filePath":"src/edu/stanford/nlp/util/Generics.java","lineNumber":194,"sourceCode":"    }\n  }\n\n  // must be called after HASH_MAP_CLASS is defined\n  private static Constructor getHashMapSizeConstructor() {\n    try {\n      return HASH_MAP_CLASS.getConstructor(Integer.TYPE);\n    } catch (Exception e) {\n      log.info(\"Warning: could not find a constructor for objects of \" + HASH_MAP_CLASS + \" which takes an integer argument.  Will use the no argument constructor instead.\");\n    }\n    return null;\n  }\n\n  // must be called after HASH_MAP_CLASS is defined\n  private static Constructor getHashMapFromMapConstructor() {\n    try {\n      return HASH_MAP_CLASS.getConstructor(Map.class);\n    } catch (Exception e) {\n      throw new RuntimeException(\"Error: could not find a constructor for objects of \" + HASH_MAP_CLASS + \" which takes an existing Map argument.\", e);\n    }\n  }\n\n  /* Maps */\n  public static <K,V> Map<K,V> newHashMap() {\n    try {\n      return ErasureUtils.uncheckedCast(HASH_MAP_CLASS.newInstance());\n    } catch (Exception e) {\n      throw new RuntimeException(e);\n    }\n  }\n\n  public static <K,V> Map<K,V> newHashMap(int initialCapacity) {\n    if (HASH_MAP_SIZE_CONSTRUCTOR == null) {\n      return newHashMap();\n    }\n    try {\n      return ErasureUtils.uncheckedCast(HASH_MAP_SIZE_CONSTRUCTOR.newInstance(initialCapacity));","sourceCodeStart":176,"sourceCodeEnd":212,"githubUrl":"https://github.com/stanfordnlp/CoreNLP/blob/1b7edd19c4d0d7b1f13a2591425b9b60a0b1af7a/src/edu/stanford/nlp/util/Generics.java#L176-L212","documentation":"Generics.newHashMap(Map) lazily looks up a Constructor<->Map constructor for the configured HASH_MAP_CLASS (a fast/linked map class chosen via system properties). If reflection cannot find a constructor accepting a Map argument, it throws this RuntimeException, meaning the configured map class is incompatible with this factory method.","triggerScenarios":"Calling Generics.newHashMap(existingMap) when the hashmap.class system property names a class that lacks a public constructor taking a Map (e.g. a class with only a no-arg constructor, an abstract class, or a typo'd class name).","commonSituations":"Setting -Dhashmap.class to a custom or newer map implementation while upgrading Stanford CoreNLP versions; typos in the fully-qualified class name; the class failing to load so reflection resolves against the wrong type.","solutions":["Check the hashmap.class (and similar) system properties; remove them to use the default java.util.HashMap subclass","Ensure the configured class is public, concrete, and has a constructor accepting java.util.Map","Verify the fully-qualified class name has no typos and is on the classpath","Call Generics.newHashMap() with no arguments and putAll(existingMap) instead"],"exampleFix":"// before\n-Dhashmap.class=com.example.MyCustomMap  // has no Map constructor\nMap<K,V> m = Generics.newHashMap(existingMap);\n// after\n-Dhashmap.class=java.util.HashMap   // or remove the property entirely\nMap<K,V> m = Generics.newHashMap(existingMap);","handlingStrategy":"validation","validationCode":"Class<?> cls = Class.forName(System.getProperty(\"hashmap.class\", \"java.util.HashMap\"));\nif (!java.util.Map.class.isAssignableFrom(cls)) throw new IllegalStateException(\"hashmap.class is not a Map\");\nboolean ok = java.util.Arrays.stream(cls.getConstructors()).anyMatch(c -> c.getParameterCount() == 1 && c.getParameterTypes()[0] == java.util.Map.class);\nif (!ok) throw new IllegalStateException(cls + \" lacks a Map constructor\");","typeGuard":null,"tryCatchPattern":"try { Map<K,V> m = Generics.newHashMap(existing); } catch (RuntimeException e) { Map<K,V> m = new HashMap<>(existing); }","preventionTips":["Do not override hashmap.class unless the class provably has a Map-arg constructor","Prefer Generics.newHashMap() (no-arg) plus putAll for maximum compatibility","Re-check system properties after upgrading CoreNLP versions"],"tags":["reflection","configuration","map"],"backgroundTag":"invalid-constructor-argument","analyzedSha":"1b7edd19c4d0d7b1f13a2591425b9b60a0b1af7a","analyzedAt":"2026-09-10T02:24:07.274Z","contentChangedAt":"2026-09-10T02:24:07.274Z","schemaVersion":2},"datasetVersion":"2026-09-17T15:17:12.973Z"}