java - 组合类和方法参数化类型

Question

我有一个这样的界面:

public interface BatchSynchronisedPool<R extends Runnable> {
    void execute(R runnable, Object batchIdentifier);
    public <T> Future<T> submit(Callable<T> callable, Object batchIdentifier);
}

我想推断 Callable 的上限，但仍希望能够保持 <T>方法参数:

public interface BatchSynchronisedPool<R extends Runnable, C extends Callable> {
    void execute(R runnable, Object batchIdentifier);
    public <T> Future<T> submit(C<T> callable, Object batchIdentifier);
}

显然这行不通，因为 C 的类型我指定可能只取一个特定范围的 T争论。但是，现在您已经大致了解了我正在尝试做的事情，是否有可能的解决方案，或者我是否总是不得不提交可调用文件？ (或者完全删除泛型并执行不安全的转换)

Answer 1

我不是 100% 确定，但不要认为您可以在这里做您想做的事情。自 C不是通用的，你不能使用 C<T> .下面有很多代码，但是 tl;dr 选择选项 3。最终真正改变的是多少BatchSynchronisedPool您需要创建的对象，这并不是一个很大的开销...

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1.保留<T>方法上的通用类型参数，提交 Callable<T>并在实现此接口(interface)的类中执行类型的运行时检查，就像您的原始解决方案一样。

public interface BatchSynchronisedPool<R extends Runnable> {
    void execute(R runnable, Object batchIdentifier);
    public <T> Future<T> submit(Callable<T> callable, Object batchIdentifier);
}

public class MyBSP<R, C> implements BatchSynchronisedPool<R, C> {
    void execute(R runnable, Object batchIdentifier) { ... }
    public <T> Future<T> submit(Callable<T> callable, Object batchIdentifier) {
        // Check types.
        if (!(callable instanceof MyDesiredCallableClass)) {
            throw new IllegalArgumentException("Types don't match.");
        }

        // Do work.
        T result = callable.call();

        ...
    }
}

public class MyUsageClass {
     public static void main(String[] args) {
         // Submit string.
         MyBSP<Runnable> bsp = new MyBSP<Runnable>();
         bsp.submit(new StringCallable(), someObject1);

         // Submit integer.
         bsp.submit(new IntegerCallable(), someObject2);
     }
}

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2.保留<T>方法上的通用类型参数，提交 C并在实现此接口(interface)的类中执行强制转换，就像您建议的那样。

public interface BatchSynchronisedPool<R extends Runnable, C extends Callable> {
    void execute(R runnable, Object batchIdentifier);
    public <T> Future<T> submit(Class<T> cls, C callable, Object batchIdentifier);
}

public class MyBSP<R, C> implements BatchSynchronisedPool<R, C> {
    void execute(R runnable, Object batchIdentifier) { ... }
    public <T> Future<T> submit(Class<T> cls, C callable, Object batchIdentifier) {
        // Do work... with a cast.
        T result = cls.cast(callable.call());

        ...
    }
}

public class MyUsageClass {
     public static void main(String[] args) {
         // Submit string.
         MyBSP<Runnable, Callable> bsp = new MyBSP<Runnable, Callable>();
         bsp.submit(new StringCallable(), someObject1);

         // Submit integer.
         bsp.submit(new IntegerCallable(), someObject2);
     }
}

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<强>3。创建一个新的 BatchSynchronisedPool对于每种类型 T 您尝试通过指定 T 提交作为类的通用类型参数。然后每次你想调用submit在不同的类型上，您需要生成 BatchSynchronisedPool 的新实例.

public interface BatchSynchronisedPool<T, R extends Runnable, C extends Callable<T>> {
    void execute(R runnable, Object batchIdentifier);
    public Future<T> submit(C callable, Object batchIdentifier);
}

public class MyBSP<T, R, C> implements BatchSynchronisedPool<T, R, C> {
    void execute(R runnable, Object batchIdentifier) { ... }
    public Future<T> submit(C callable, Object batchIdentifier) {
        // Do work.  Types are okay; no checking or casting needed!
        T result = callable.call();

        ...
    }
}

public class MyUsageClass {
     public static void main(String[] args) {
         // Submit string.
         MyBSP<String, Runnable, Callable<String>> stringBsp = new MyBSP<String, Runnable, Callable<String>>();
         stringBsp.submit(new StringCallable(), someObject1);

         // Submit integer.
         MyBSP<Integer, Runnable, Callable<Integer>> integerBsp = new MyBSP<Integer, Runnable, Callable<Integer>>();
         integerBsp.submit(new IntegerCallable(), someObject2);
     }
}