[英]How to get constructor of a class with a generic parameter in the constructor
The problem: To get parameterized constructor reference of subclasses of A (such as class H shown below) in class C. 问题:要获取类C中A的子类(例如下面显示的类H)的参数化构造函数引用。
Class A<T extends B> {
public A(T objectT, D objectD, E objectE, F objectF) {
}
public T aMethodWithTAsReturnType();
}
Class B { }
Class C<T extends A<?>> {
private Constructor<?> classAConstructor;
public C(Class<T> classA) {
classAConstructor=classA.getConstructor(B.class, D.class,E.class,F.class)
}
}
Class H extends A<X> {
public H(X objectX, D objectD, E objectE, F objectF) {}
}
Class X extends B {}
new C(new H(objectX,objectD,objectE,objectF));
The above code configuration would result in a NoSuchMethodException
when a new Class C object is created because it cannot find the constructor for Class A 创建新的Class C对象时,上述代码配置将导致
NoSuchMethodException
,因为它找不到Class A的构造函数
I am now trying to use: 我现在正在尝试使用:
Method methodInA = classA.getMethod('aMethodWithTAsReturnType')
Class<?> TClassInA = methodInA.getReturnType();
as a replacement for B.class
in the classA.getConstructor
line as I'm guessing that's the issue here because class B is a super type of T (in Class A). 作为
classA.getConstructor
行中B.class
的替代品,因为我猜这里是问题所在,因为类B是T的超类型(在类A中)。
However... when I used methodInA.getReturnType() it returns B.class! 但是...当我使用methodInA.getReturnType()时,它返回B.class! rather than a class that has extended B. I then found a
getGenericReturnType()
method but it returns a Type object. 而不是扩展了B的类。然后,我找到了
getGenericReturnType()
方法,但是它返回Type对象。
This works for me: 这对我有用:
public class G {
static class A<T extends B> {
A(T objectT, D objectD, E objectE, F objectF) { }
}
static class B { }
static class C<XT extends B, T extends A<XT>> {
private Constructor<?> classAConstructor;
public C(Class<T> classA, Class<XT> classX) throws SecurityException,
NoSuchMethodException {
classAConstructor = classA.getConstructor(classX, D.class,
E.class, F.class);
}
}
static class D { }
static class E { }
static class F { }
static class X extends B { }
public static class H extends A<X> {
public H(X objectT, D objectD, E objectE, F objectF) {
super(objectT, objectD, objectE, objectF);
}
}
public static void main(String[] args) throws SecurityException,
NoSuchMethodException {
new C<X, H>(H.class, X.class);
}
}
UPDATE: You will need to find some way of passing the parameterisation of A into C. I've updated your code to illustrate one way of doing so. 更新:您将需要找到一种将A的参数化传递给C的方法。我已经更新了您的代码以说明这样做的一种方法。
getConstructor()
returns only public constructors. getConstructor()
仅返回公共构造函数。 Try with getDeclaredConstructor()
. 尝试使用
getDeclaredConstructor()
。
EDIT: 编辑:
The problem is that the H constructor doesn't take a B as argument, but a X (which is a subclass of B). 问题在于H构造函数没有将B作为参数,而是X(它是B的子类)。 The signature of the constructor is thus
H(X, D, E, F)
. 因此,构造函数的签名为
H(X, D, E, F)
。 This constructor only accepts instances of X
as its first argument. 此构造函数仅接受
X
实例作为其第一个参数。 It doesn't accept any kind of B
instances, but only instances of X
. 它不接受任何类型的
B
实例,仅接受X
实例。
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