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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Java] StructVector throws with ExtensionType","articleBody":"### Describe the bug, including details regarding any error messages, version, and platform.\n\nCurrently when creating a struct vector with a child being an extension type things throw:\r\n```java\r\n  @Test\r\n  public void testStructVectorWithExtensionTypes() {\r\n    TestExtensionType.UuidType uuidType = new TestExtensionType.UuidType();\r\n    Field uuidField =  new Field(\"struct_child\", FieldType.nullable(uuidType), null);\r\n    Field structField = new Field(\"struct\", FieldType.nullable(new ArrowType.Struct()), List.of(uuidField));\r\n    // throws\r\n    StructVector s1 = new StructVector(structField, allocator, null);\r\n    // doesn't throw\r\n    StructVector s2 = (StructVector) structField.createVector(allocator);\r\n    s1.close();\r\n    s2.close();\r\n  }\r\n```\r\n\r\nI am mainly running into this while trying to create a `TransferPair`.\r\n```java\r\n  @Test\r\n  public void testStructVectorTransferPairWithExtensionType() {\r\n    TestExtensionType.UuidType uuidType = new TestExtensionType.UuidType();\r\n    Field uuidField =  new Field(\"uuid_child\", FieldType.nullable(uuidType), null);\r\n    Field structField = new Field(\"struct\", FieldType.nullable(new ArrowType.Struct()), List.of(uuidField));\r\n\r\n    StructVector s1 = (StructVector) structField.createVector(allocator);\r\n    TestExtensionType.UuidVector uuidVector = s1.addOrGet(\"uuid_child\", FieldType.nullable(uuidType), TestExtensionType.UuidVector.class);\r\n    s1.setValueCount(1);\r\n    uuidVector.set(0, new UUID(1, 2));\r\n    s1.setIndexDefined(0);\r\n\r\n    TransferPair tp = s1.getTransferPair(structField, allocator);\r\n    final StructVector toVector = (StructVector) tp.getTo();\r\n    assertEquals(s1.getField(), toVector.getField());\r\n    assertEquals(s1.getField().getChildren().get(0), toVector.getField().getChildren().get(0));\r\n    // also fails but probably another issue\r\n//    assertEquals(s1.getValueCount(), toVector.getValueCount());\r\n//    assertEquals(s1, toVector);\r\n\r\n    s1.close();\r\n    toVector.close();\r\n  }\r\n```\n\n### Component(s)\n\nJava","author":{"url":"https://github.com/FiV0","@type":"Person","name":"FiV0"},"datePublished":"2024-05-20T10:58:20.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/87/arrow-java/issues/87"}