संकलित करें: " '<>' अनाम वर्गों के साथ इस्तेमाल किया नहीं किया जा सकता"

Question

मैं इतना बल्कि यह लिखने के लिए करना चाहते हैं:

Lists.transform(vals, 
    new Function<>() { 
     public List<ValEntry> apply(Validator<? super T> input) { 
      return input.validate(value); 
     } 
    }); 

... इस से:

Lists.transform(vals, 
    new Function<Validator<? super T>, List<ValEntry>>() { 
     public List<ValEntry> apply(Validator<? super T> input) { 
      return input.validate(value); 
     } 
    }); 

लेकिन जावा कंपाइलर मुझे निम्न त्रुटि संदेश देता है:

'<>' cannot be used with anonymous classes 

क्या इसके लिए कोई मौलिक कारण है? या सिर्फ जेडीके 7 में फीचर को छोड़ दिया, शायद वे इसे 8 में करते हैं?

Answer 1

project coin documentation के अनुसार:

Internally, a Java compiler operates over a richer set of types than those that can be written down explicitly in a Java program. The compiler-internal types which cannot be written in a Java program are called non-denotable types. Non-denotable types can occur as the result of the inference used by diamond. Therefore, using diamond with anonymous inner classes is not supported since doing so in general would require extensions to the class file signature attribute to represent non-denotable types, a de facto JVM change. It is feasible that future platform versions could allow use of diamond when creating an anonymous inner class as long as the inferred type was denotable.

संपादित तो यह एक भविष्य संस्करण में संभव है। यह जावा 8 के साथ अभी भी संभव नहीं है, लेकिन अब हमारे पास भेड़ का बच्चा है, इसलिए इसकी आवश्यकता कम है।

Answer 2

यह अब जावा 9. में शामिल किया जाना निर्धारित है JEP 213: Milling Project Coin से:

3. Allow diamond with anonymous classes if the argument type of the inferred type is denotable . Because the inferred type using diamond with an anonymous class constructor could be outside of the set of types supported by the signature attribute, using diamond with anonymous classes was disallowed in Java SE 7. As noted in the JSR 334 proposed final draft, it would be possible to ease this restriction if the inferred type was denotable.