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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Upstream Bug: JsonNumber.of(double) hardcodes decimalOffset causing toLong to fail","articleBody":"## Summary\n\nThe `JsonNumber.of(double)` factory method has a bug where it hardcodes `decimalOffset=0` and `exponentOffset=0` when creating the `JsonNumberImpl`. This causes `toLong()` to fail for integral doubles like `123.0`.\n\n## Root Cause\n\nIn `JsonNumber.java` line 117:\n```java\nstatic JsonNumber of(double num) {\n    if (!Double.isFinite(num)) {\n        throw new IllegalArgumentException(\"Not a valid JSON number\");\n    }\n    var str = Double.toString(num);\n    return new JsonNumberImpl(str.toCharArray(), 0, str.length(), 0, 0);\n    //                                                           ^^^^^ BUG: hardcoded offsets\n}\n```\n\nFor `Double.toString(123.0)` which returns `\"123.0\"`:\n- `decimalOffset` should be `3` (position of `.`) but is passed as `0`\n- This causes `initNumLong()` in `JsonNumberImpl` to misparse the number\n\n## Reproduction\n\n```java\nvar jn = JsonNumber.of(123.0);\njn.toString();  // \"123.0\" - OK\njn.toDouble();  // 123.0 - OK\njn.toLong();    // THROWS: \"123.0 cannot be represented as a long\"\n                // EXPECTED: 123L (per API docs, \"123.0\" should be convertible)\n```\n\n## Comparison with Json.parse()\n\n```java\nvar parsed = Json.parse(\"123.0\");\nparsed.toLong();  // 123L - WORKS correctly\n```\n\nThe difference is that `Json.parse()` correctly computes the `decimalOffset` during parsing.\n\n## Suggested Fix\n\nOption 1 - Reuse `JsonNumber.of(String)` which delegates to parser:\n```java\nstatic JsonNumber of(double num) {\n    if (!Double.isFinite(num)) {\n        throw new IllegalArgumentException(\"Not a valid JSON number\");\n    }\n    return JsonNumber.of(Double.toString(num));\n}\n```\n\nOption 2 - Compute correct offsets:\n```java\nstatic JsonNumber of(double num) {\n    if (!Double.isFinite(num)) {\n        throw new IllegalArgumentException(\"Not a valid JSON number\");\n    }\n    var str = Double.toString(num);\n    var chars = str.toCharArray();\n    int dec = str.indexOf('.');\n    int exp = str.indexOf('e');\n    if (exp == -1) exp = str.indexOf('E');\n    return new JsonNumberImpl(chars, 0, chars.length, \n        dec == -1 ? -1 : dec, \n        exp == -1 ? -1 : exp);\n}\n```\n\n## This is an Upstream Bug\n\nThis bug exists in OpenJDK jdk-sandbox `json` branch at commit `91a479d`. The upstream tests in `TestJsonNumber.java` do not cover this case - they test `of(double).toDouble()` but never `of(double).toLong()` for integral doubles.\n\n## Affected Versions\n\n- jdk-sandbox json branch (upstream)\n- java.util.json.Java21 backport 0.1.9 (this repo, synced from upstream)\n","author":{"url":"https://github.com/simbo1905","@type":"Person","name":"simbo1905"},"datePublished":"2026-01-26T00:14:19.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/118/java.util.json.Java21/issues/118"}