java （泛型）不能对非静态类型 T 进行静态引用
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(Generics)Cannot make a static reference to the non-static type T
提问by securenova
running the Demo class will invoke a static method newInstance in SomeClass to call the constructor and printing hello
运行Demo类会调用SomeClass中的静态方法newInstance来调用构造函数并打印hello
defining a method will include a return type + method name with arguments
定义一个方法将包括一个返回类型+带有参数的方法名称
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>
newInstance 的返回类型是 <T>SomeClass<T> 对我来说似乎很奇怪，因为我的类被称为 SomeClass<T> 而不是 <T>SomeClass<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
为什么我需要在 SomeClass<T> 前面的 <T> ？似乎如果我不包含它，就会出现一个名为无法对非静态类型 T 进行静态引用的常见错误
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.
另一件事要指出的是，我可以在 <T> 和 SomeClass<T> 之间放置许多空格，因此它们似乎不需要在一起。
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);
}
}
回答by Jorn Vernee
What is a static method? A Method that works on the class, and not a specific instance. The generic parameter Tin 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].
什么是静态方法？一个在类上工作的方法，而不是一个特定的实例。T类签名中的泛型参数public class SomeClass<T>仅适用于特定实例（因此non-static type T）。例如SomeClass<String>在哪里[T = String]。
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 Tis separate from the Tin the class signature. So it might as well be Ci.e. public static <C> SomeClass<C> newInstance(Class<C> clazz). Or something completely different.
通过包含<T>在 的方法签名中public static <T>SomeClass<T> newInstance(Class<T> clazz)。你是这么说的；对于此方法，有一个泛型类型参数T。这T是从不同的T类中的签名。所以它也可能是Cie public static <C> SomeClass<C> newInstance(Class<C> clazz)。或者完全不同的东西。
But if you don't include <T>with the method, the compiler thinks you're trying to use the Tin the class signature. Which is illegal.
但是如果您不包含<T>在方法中，编译器会认为您正在尝试T在类签名中使用 。这是非法的。
