(泛型)无法静态引用非静态类型T [英] (Generics)Cannot make a static reference to the non-static type T
问题描述
运行Demo类将在SomeClass中调用静态方法newInstance来调用构造函数并打印问候
running the Demo class will invoke a static method newInstance in SomeClass to call the constructor and printing hello
定义方法将包括带有参数的返回类型+方法名称
defining a method will include a return type + method name with arguments
newInstance的返回类型是< T> SomeClass< T>在我看来很奇怪 因为我的班级叫做SomeClass< T>而不是< T> SomeClass< T>
the return type for newInstance is <T>SomeClass<T> seems weird to me since my class is called SomeClass<T> instead of <T>SomeClass<T>
为什么我需要在SomeClass< T>前面的< T>? 似乎如果我不包括它，将会出现一个常见错误 不能静态引用非静态类型T
why do i need the <T> in front of the SomeClass<T> ? it seems that if I don't include it there will be an common error called Cannot make a static reference to the non-static type T
要指出的另一件事是，我可以在< T>和SomeClass< T>之间放置很多空格，这样看来它们并不需要在一起.
another thing to point out is that I can put many spaces between <T> and SomeClass<T> so it doesn't seem like they need to be together.
public class SomeClass<T> {
public static <T>SomeClass<T> newInstance(Class<T> clazz){
return new SomeClass<T>(clazz);
}
private SomeClass(Class<T> clazz){
System.out.println("hello");
}
}
public class Demo {
public static void main(String args[])
{
SomeClass<String> instance = SomeClass.newInstance(String.class);
}
}
推荐答案
什么是静态方法?该方法适用于该类，而不适用于特定实例.类签名public class SomeClass<T>中的通用参数T仅可用于特定实例(因此为non-static type T).例如SomeClass<String>其中[T = String].
What is a static method? A Method that works on the class, and not a specific instance. The generic parameter T in the class signature public class SomeClass<T> is only available for a specific instance (hence non-static type T). e.g. SomeClass<String> where the [T = String].
通过在public static <T>SomeClass<T> newInstance(Class<T> clazz)的方法签名中包含<T>.你是在说对于此方法，有一个通用类型参数T.该T与类签名中的T是分开的.因此也可能是C，即public static <C> SomeClass<C> newInstance(Class<C> clazz).或完全不同的东西.
By including <T> in the method signature of public static <T>SomeClass<T> newInstance(Class<T> clazz). You're saying that; for this method, there is a generic type argument T. This T is separate from the T in the class signature. So it might as well be C i.e. public static <C> SomeClass<C> newInstance(Class<C> clazz). Or something completely different.
但是，如果您不将<T>包含在该方法中，则编译器会认为您正在尝试在类签名中使用T.这是非法的.
But if you don't include <T> with the method, the compiler thinks you're trying to use the T in the class signature. Which is illegal.
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