Java 8對泛型方法的調用含糊不清[重復]
[英]Java 8 call to generic method is ambiguous [duplicate]
This question already has an answer here:
這個問題在這里已有答案:
- Java type inference: reference is ambiguous in Java 8, but not Java 7 2 answers
Java類型推斷:Java 8中引用不明確,但Java 7 2答案不明確
I'm porting Java7 code to Java8, and I came up with a following problem. In my codebase I have two methods:
我正在將Java7代碼移植到Java8,我想出了以下問題。在我的代碼庫中,我有兩種方法:
public static <T> ImmutableSet<T> append(Set<T> set, T elem) {
return ImmutableSet.<T>builder().addAll(set).add(elem).build();
}
public static <T> ImmutableSet<T> append(Set<T> set, Set<T> elemSet) {
ImmutableSet.Builder<T> newSet = ImmutableSet.builder();
return newSet.addAll(set).addAll(elemSet).build();
Compiler returns error about ambiguous match for method append in following test:
編譯器在以下測試中返回有關方法附加的模糊匹配的錯誤:
@Test(expected = NullPointerException.class)
public void shouldAppendThrowNullPointerForNullSecondSet() {
ImmutableSet<Integer> obj = null;
CollectionUtils.append(ImmutableSet.of(1), obj);
}
Compiler error:
reference to append is ambiguous both method append(java.util.Set,T) in CollectionUtils and method append(java.util.Set,java.util.Set) in CollectionUtils match
對append的引用是不明確的,CollectionUtils中的方法append(java.util.Set,T)和CollectionUtils中的方法append(java.util.Set,java.util.Set)匹配
How to rewrite these functions to work with type inference from introduced with Java8?
如何重寫這些函數以使用Java8引入的類型推斷?
1 个解决方案
#1
7
You've found the new Generalized Target-type Inference improvements in Java 8. There's a few stack overflow questions on it. Such as this one.
您已經在Java 8中找到了新的通用目標類型推斷改進。它上面有一些堆棧溢出問題。比如這個。
Java 8 can infer the return type of a generic based on the method it's passed to as an argument. So when you call CollectionUtils.append(ImmutableSet.of(1), obj), Java 8 is attempting to return an immutable set from the static of call that matches one of your append methods. In this instance, it could think about returning a ImmutableSet<Object> instead of the ImmutableSet<Integer> that you're clearly trying to return. And then it's unclear if you're calling append(Set<Object>, Object), or append(Set<Integer>, Set<Integer>).
Java 8可以根據它作為參數傳遞給的方法推斷泛型的返回類型。因此,當您調用CollectionUtils.append(ImmutableSet.of(1),obj)時,Java 8會嘗試從與您的某個追加方法匹配的調用靜態返回一個不可變集。在這個例子中,它可以考慮返回一個ImmutableSet
The easiest solution is to rename the second method appendAll. Or, you could follow the suggested fix here and change your call to something like :
最簡單的解決方案是重命名第二個方法appendAll。或者,您可以按照建議的修復方式將您的呼叫更改為:
CollectionUtils.append(ImmutableSet.<ImmutableSet<Integer>>of(1), obj);
I'd stick with renaming the second method myself though. It will save other developers the same grief when they try to use the library.
我堅持自己重命名第二種方法。當他們嘗試使用該庫時,它將為其他開發人員帶來同樣的悲痛。
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