在抽象超类中使用子类的泛型类型？ [英] Using a generic type of a subclass within it's abstract superclass?

问题描述

在我的代码中，有以下抽象超类

Within my code a have the following abstract superclass

public abstract class AbstractClass<Type extends A> {...}

以及一些子类，例如

public class ChildClassA extends AbstractClass<GenericTypeA> {...}

public class ChildClassB extends AbstractClass<GenericTypeB> {...}

我正在寻找一种优雅的方式来使用通用类型

I'm searching for an elegant way how I can use the generic type of the child classes (GenericTypeA, GenericTypeB, ...) inside the abstract class in a generic way.

为了解决这个问题，我目前定义了方法

To solve this problem I currently defined the method

protected abstract Class<Type> getGenericTypeClass();

在我的抽象类中并实现了方法

in my abstract class and implemented the method

@Override
protected Class<GenericType> getGenericTypeClass() {
    return GenericType.class;
}

每个孩子班级。

是否可以在不实现此辅助方法的情况下获得抽象类中子类的泛型？

Is it possible to get the generic type of the child classes in my abstract class without implementing this helper method?

BR，

马库斯

推荐答案

我认为这是可能的。我看到它与泛型一起在DAO模式中使用。例如
考虑类别：

I think its possible. I saw this was being used in the DAO patterns along with generics. e.g. Consider classes:

public class A {}
public class B extends A {}

和您的通用类：

  import java.lang.reflect.ParameterizedType;
  public abstract class Test<T extends A> {

     private Class<T> theType;

     public Test()  {
        theType = (Class<T>) (
               (ParameterizedType) getClass().getGenericSuperclass())
              .getActualTypeArguments()[0];
     }

     // this method will always return the type that extends class "A"
     public Class<T> getTheType()   {
        return theType;
     }

     public void printType() {
        Class<T> clazz = getTheType();
        System.out.println(clazz);
     }
  }

您可以拥有一个Test1类，该类通过类扩展了Test B（它扩展了A）

You can have a class Test1 that extends Test with class B (it extends A)

  public class Test1 extends Test<B>  {

     public static void main(String[] args) {
        Test1 t = new Test1();

        Class<B> clazz = t.getTheType();

        System.out.println(clazz); // will print 'class B'
        System.out.println(printType()); // will print 'class B'
     }
  }

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