3

是否可以在 java 的接口内部有一个内部类？？？

4

7 回答 7

3

You can. But here's what O'Reilly says about it:

Nested Classes in Interfaces?

Java supports the concept of nested classes in interfaces. The syntax and dynamics work just like nested classes declared in a class. However, declaring a class nested inside an interface would be extremely bad programming. An interface is an abstraction of a concept, not an implementation of one. Therefore, implementation details should be left out of interfaces. Remember, just because you can cut off your hand with a saw doesn't mean that it's a particularly good idea.

That said, I could see an argument for a static utility class nested into an interface. Though why it would need to be nested into the interface instead of being a stand-alone class is completely subjective.

于 2010-08-01T16:32:33.820 回答
2

我同意这通常很少见，但是当接口方法需要返回多条信息时，我确实喜欢在接口中使用内部类来提供服务，因为它实际上是合同的一部分，而不是实现的一部分。例如：

public interface ComplexOperationService {

    ComplexOperationResponse doComplexOperation( String param1, Object param2 );

    public static class ComplexOperationResponse {
        public int completionCode;
        public String completionMessage;
        public List<Object> data;
        // Or use private members & getters if you like...
    }

}

显然，这也可以在一个单独的类中完成，但对我来说，感觉就像我将接口定义的整个 API 保持在一个位置，而不是分散开来。

于 2010-08-01T18:35:53.960 回答
1

Yes, it is possible but it is not common practice.

interface Test
{
    class Inner
    { }
}

class TestImpl implements Test
{
    public static void main(String[] arg)
    {
        Inner inner = new Inner();
    }
}
于 2010-08-01T16:30:33.430 回答
1

不直接回答您的问题，但在相关说明中，您还可以将一个接口嵌套在另一个接口中。这是可以接受的，特别是如果您想提供意见。Java 的集合类执行此操作，例如Map.java在Map.Entry视图的情况下：

public interface Map<K,V> {
   ...
   public static interface Entry<K,V> {
       ....
   }
}

这是可以接受的，因为您没有将实现细节混合到您的界面中。您只是在指定另一个合同。

于 2010-08-01T16:59:24.697 回答
0

Yes. Straight from the language spec:

An inner class is a nested class that is not explicitly or implicitly declared static.

And (boldface mine):

A nested class is any class whose declaration occurs within the body of another class or interface.

于 2010-08-01T16:34:22.893 回答
0

这是合法的，但我只使用嵌套接口（如前所述）或嵌套枚举。例如：

public interface MyInterface {

    public enum Type { ONE, TWO, THREE }

    public Type getType();

    public enum Status { GOOD, BAD, UNKNOWN }

    public Status getStatus();

}
于 2010-08-01T17:43:47.453 回答
0

我发现一个非常有用的用例是，如果您有一个创建接口实例的构建器。如果构建器是接口的静态成员，您可以像这样创建一个实例：

DigitalObject o = new DigitalObject.Builder(content).title(name).build();
于 2010-08-01T17:11:39.653 回答