英文:
Inexplicable behaviour of overloaded method using generics
问题
class My<T> {
void overloadMethod(String s) {
System.out.println("string");
}
void overloadMethod(Integer i) {
System.out.println("integer");
}
void overloadMethod(T t) {
System.out.println("t");
}
}
public class MyClass01 {
public static void main(String[] args) {
String o = "abc";
new My<String>().overloadMethod(o);
}
}
这导致了以下错误：
/MyClass01.java:20: 错误: 对overloadMethod的引用不明确
new My<String>().overloadMethod(o);
^
My中的overloadMethod(String)和My中的overloadMethod(T)都匹配
其中T是类型变量:
T extends Object 在My类中声明
1 个错误
我原本期望会输出 "string"，假设类型擦除会确保第三个方法是：
void overloadMethod(Object t) {
System.out.println("t");
}
我在这里漏掉了什么？谢谢。
英文:
class My<T> {
void overloadMethod(String s) {
System.out.println("string");
}
void overloadMethod(Integer i) {
System.out.println("integer");
}
void overloadMethod(T t) {
System.out.println("t");
}
}
public class MyClass01 {
public static void main(String[] args) {
String o = "abc";
new My<String>().overloadMethod(o);
}
}
This gives the following error:
/MyClass01.java:20: error: reference to overloadMethod is ambiguous
new My<String>().overloadMethod(o);
^
both method overloadMethod(String) in My and method overloadMethod(T) in My match
where T is a type-variable:
T extends Object declared in class My
1 error
I was expecting "string" output assuming that type erasure would ensure that the third method would be:
void overloadMethod(Object t) {
System.out.println("t");
}
What am I missing here?
Thanks.
答案1
得分: 1
通过将通用class MyClass<T>实例化为特定参数化类型new My<String>().overloadMethod(o);，您已经_有效地_声明了两个具有相同签名的方法：overloadMethod(String s)。
这就是编译器错误尝试用以下内容告诉您的原因：„error: reference to overloadMethod is ambiguous“。
> „…我在这里漏掉了什么吗？…“
因为您说：“我期望得到"string"输出”，听起来您错误地认为您对_class My<T>的声明以某种方式赋予了您的非通用方法overloadMethod(String s)_具有参数化多态性的能力。实际上并没有。
英文:
By instantiating the generic class MyClass<T> into the specific parameterized type new My<String>().overloadMethod(o);, you've effectively declared two methods with this same signature: overloadMethod(String s).
That's what the compiler error is trying to tell you with: „error: reference to overloadMethod is ambiguous“.
> „…What am I missing here?…“
Because you say: „I was expecting "string" output“, it sounds like you're mistakenly assuming that your declaration of class My<T> has somehow imbued your non-generic method overloadMethod(String s) with the powers of parametric polymorphism. It hasn't.
答案2
得分: -1
问题出在 void overloadMethod(T t) 这里，这里的 T 是泛型类，在声明时可以是任何类型，当你声明 new My<String>() 时，T = String，如果尝试注释掉 overloadMethod(String s)，你会得到 "t" 作为输出。这里的歧义在于在这种情况下 T = String，所以类中有两个可以调用的方法：
void overloadMethod(String s) = void overloadMethod(T t)
而不知道调用哪一个。
英文:
The problem is the void overloadMethod(T t), here T is generic Class, it could be anything, when you declared
new My<String>() then T = String
try to comment in the overloadMethod(String s), you will get "t" as output
The ambiguity comes into play since T = String in this case, so the class has 2 methods to call
void overloadMethod(String s) = void overloadMethod(T t)
And doesn't know wich one to call
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