java - 在 Java 中使用泛型和类型推断的问题

Question

这段时间我在做一个需要某种抽象的项目，但我不知道如何解决一些与java泛型和类型推断相关的问题。

这是源代码的简化架构:

public abstract class BaseDataset
{
    // Some data
    // Some methods
}

public class DerivedDataset1 extends BaseDataset
{
    // Some data
    // Implementations of some BaseDataset methods
    // Some additional methods
}

public class DerivedDataset2 extends BaseDataset
{
    // Some data
    // Implementations of some BaseDataset methods
    // Some additional methods
}

public interface BaseMeasure<T extends BaseDataset>
{
    public float evaluate(T dataset);
}

public class DerivedMeasure1 implements BaseMeasure<DerivedDataset1>
{
    @Override
    public float evaluate(DerivedDataset1 dataset)
    {
        // evaluate some measure using DerivedDataset1 methods
        return the evaluated measure;
    }
}

public class DerivedMeasure2 implements BaseMeasure<DerivedDataset2>
{
    @Override
    public float evaluate(DerivedDataset1 dataset)
    {
        // evaluate some measure using DerivedDataset2 methods
        return the evaluated measure;
    }
}

public class SocialNetworkBuilder
{
    public <T extends BaseDataset> void build(T dataset, BaseMeasure<T> measure)
    {
        float weight = measure.evaluate(dataset);

        // ...
    }
}

我的问题是，如果在我的主课中，我写了这样的东西:

public class Application
{
    public static void main(String [] args)
    {
        BaseDataset dataset = new DerivedDataset1();
        BaseMeasure<? extends BaseDataset> measure = new DerivedMeasure1();
        SocialNetworkBuilder socialNetworkBuilder = new SocialNetworkBuilder();
        socialNetworkBuilder.build(dataset, measure);
    }
}

Eclipse 给我错误:“SocialNetworkBuilder 类型的方法 build(T, BaseMeasure) 不适用于参数 (BaseDataset, BaseMeasure)”

我认为问题在于“构建”方法必须确保数据集和度量属于同一类型 T。

如果我这样做:

public class Application
{
    public static void main(String [] args)
    {
        BaseDataset dataset = new DerivedDataset1();
        BaseMeasure<? extends BaseDataset> measure = new DerivedMeasure1();
        SocialNetworkBuilder socialNetworkBuilder = new SocialNetworkBuilder();
        socialNetworkBuilder.build((DerivedDataset1) dataset, (DerivedMeasure1) measure);
    }
}

它有效，但我不能用这种方式解决我的问题，因为我在编译时不知道我的“数据集”和“测量”实例的派生类型； “dataset”和“measure”应该根据运行时给定的一些参数实例化。

我需要在运行时实例化我的“measure”和“dataset”变量，并且仍然能够对它们调用“build”方法。

你有什么想法可以解决这个问题吗？

谢谢。

Answer 1

当您按如下方式更改应用程序时，您的应用程序将编译:

public class Application
{
    public static void main(String [] args)
    {
        DerivedDataset1 dataset = new DerivedDataset1();
        BaseMeasure<DerivedDataset1> measure = new DerivedMeasure1();
        SocialNetworkBuilder socialNetworkBuilder = new SocialNetworkBuilder();
        socialNetworkBuilder.build(dataset, measure);
    }
}