{"record":{"id":"050fc495a1950e39","repo":"stanfordnlp/CoreNLP","slug":"error-could-not-find-a-constructor-for-objects-of","errorCode":null,"errorMessage":"Error: could not find a constructor for objects of ${HASH_SET_CLASS} which takes an existing collection argument.","messagePattern":"Error: could not find a constructor for objects of (.+?) which takes an existing collection argument\\.","errorType":"exception","errorClass":"RuntimeException","httpStatus":null,"severity":"error","filePath":"src/edu/stanford/nlp/util/Generics.java","lineNumber":130,"sourceCode":"    }\n  }\n\n  // must be called after HASH_SET_CLASS is defined\n  private static Constructor getHashSetSizeConstructor() {\n    try {\n      return HASH_SET_CLASS.getConstructor(Integer.TYPE);\n    } catch (Exception e) {\n      log.info(\"Warning: could not find a constructor for objects of \" + HASH_SET_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_SET_CLASS is defined\n  private static Constructor getHashSetCollectionConstructor() {\n    try {\n      return HASH_SET_CLASS.getConstructor(Collection.class);\n    } catch (Exception e) {\n      throw new RuntimeException(\"Error: could not find a constructor for objects of \" + HASH_SET_CLASS + \" which takes an existing collection argument.\", e);\n    }\n  }\n\n  public static <E> Set<E> newHashSet() {\n    try {\n      return ErasureUtils.uncheckedCast(HASH_SET_CLASS.newInstance());\n    } catch (Exception e) {\n      throw new RuntimeException(e);\n    }\n  }\n\n  public static <E> Set<E> newHashSet(int initialCapacity) {\n    if (HASH_SET_SIZE_CONSTRUCTOR == null) {\n      return newHashSet();\n    }\n    try {\n      return ErasureUtils.uncheckedCast(HASH_SET_SIZE_CONSTRUCTOR.newInstance(initialCapacity));\n    } catch (Exception e) {","sourceCodeStart":112,"sourceCodeEnd":148,"githubUrl":"https://github.com/stanfordnlp/CoreNLP/blob/1b7edd19c4d0d7b1f13a2591425b9b60a0b1af7a/src/edu/stanford/nlp/util/Generics.java#L112-L148","documentation":"Generics.getHashSetCollectionConstructor reflectively looks up a HashSet constructor accepting a Collection (the configured HASH_SET_CLASS) and throws RuntimeException wrapping the reflective failure if none exists. This occurs at static initialization time when building the HASH_SET_COLLECTION_CONSTRUCTOR holder.","triggerScenarios":"Static initialization of Generics when HASH_SET_CLASS does not declare a public Constructor(Collection) — e.g. a custom set class substituted via configuration that lacks the Collection-arg constructor, or NoSuchMethodException/SecurityException during reflection.","commonSituations":"Swapping in a non-standard Set implementation whose constructor signatures differ; unusual JDK/security-manager environments blocking reflection; classpath changes replacing the expected class.","solutions":["Ensure HASH_SET_CLASS (default java.util.HashSet) exposes a public constructor taking Collection; revert to HashSet if customized.","Add the missing constructor to the custom set class: public MySet(Collection<? extends E> c).","Check for classpath conflicts pulling in an unexpected HASH_SET_CLASS implementation.","Inspect the wrapped cause (e.getCause()) to confirm whether it is NoSuchMethodException vs. a security/ClassNotFound problem and fix accordingly."],"exampleFix":"// before\npublic class MySet<E> extends AbstractSet<E> { public MySet() {...} } // no Collection ctor\n// after\npublic class MySet<E> extends AbstractSet<E> {\n  public MySet() {...}\n  public MySet(Collection<? extends E> c) { addAll(c); }\n}","handlingStrategy":"try-catch","validationCode":"try { HASH_SET_CLASS.getConstructor(Collection.class); } catch (NoSuchMethodException e) { /* configured set class lacks Collection ctor */ }","typeGuard":"boolean hasCollectionConstructor(Class<?> cls) { try { cls.getConstructor(Collection.class); return true; } catch (Exception e) { return false; } }","tryCatchPattern":"try { Set<E> s = Generics.newHashSet(existing); } catch (RuntimeException e) { Set<E> s = new HashSet<>(existing); }","preventionTips":["Keep HASH_SET_CLASS at java.util.HashSet unless the replacement has a Collection constructor","Verify custom Set classes expose public MySet(Collection)","Catch ExceptionInInitializerError/NoClassDefFoundError around first Generics use to diagnose static-init failures","Inspect getCause() of the RuntimeException to identify the reflective failure"],"tags":["java","reflection","static-initialization","collections"],"backgroundTag":"class-not-found","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"}