在匿名类中实现两个接口

I have two interfaces:

我有两个接口：

interface A {
    void foo();
}

interface B {
    void bar();
}

I am able to create anonymous instances of classes implementing either of these interfaces like so:

我能够创建实现这些接口的类的匿名实例，如下所示：

new A() {
    void foo() {}
}

or:

要么：

new B() {
    void bar() {}
}

I want to create an anonymous class that implements both interfaces. Something like (the fictitious):

我想创建一个实现两个接口的匿名类。像（虚构的）：

new A implements B {
    void foo() {}
    void bar() {}
}

This obviously gives a compile error: "B cannot be resolved to a type".

这显然会产生编译错误：“B无法解析为类型”。

The workaround is quite simple:

解决方法很简单：

class Aggregate implements A, B {
    void foo() {}
    void bar() {}
}

I then use Aggregate where ever I would have used the anonymous class.

然后我使用Aggregate，我将使用匿名类。

I was wondering if it is even legal for an anonymous class to implement two interfaces.

我想知道一个匿名类实现两个接口是否合法。

4 个解决方案

#1

"An anonymous inner class can extend one subclass or implement one interface. Unlike non-anonymous classes (inner or otherwise), an anonymous inner class cannot do both. In other words, it cannot both extend a class and implement an interface, nor can it implement more than one interface. " (http://scjp.wikidot.com/nested-classes)

“匿名内部类可以扩展一个子类或实现一个接口。与非匿名类（内部或其他）不同，匿名内部类不能同时执行这两种操作。换句话说，它不能同时扩展类并实现接口，也不能它实现了多个接口。“（http://scjp.wikidot.com/nested-classes）

#2

If you are determined to do this, you could declare a third interface, C:

如果您决定这样做，您可以声明第三个接口，C：

public interface C extends A, B {
}

In this way, you can declare a single anonymous inner class, which is an implementation of C.

通过这种方式，您可以声明一个匿名内部类，这是C的一个实现。

A complete example might look like:

完整的示例可能如下所示：

public class MyClass {

  public interface A {
    void foo();
  }

  public interface B {
    void bar();
  }

  public interface C extends A, B {
    void baz();
  }

  public void doIt(C c) {
    c.foo();
    c.bar();
    c.baz();
  }

  public static void main(String[] args) {
    MyClass mc = new MyClass();

    mc.doIt(new C() {
      @Override
      public void foo() {
        System.out.println("foo()");
      }

      @Override
      public void bar() {
        System.out.println("bar()");
      }

      @Override
      public void baz() {
        System.out.println("baz()");
      }
    });
  }

}

The output of this example is:

这个例子的输出是：

foo()
bar()
baz()

#3

For save some keystrokes (for example if the interfaces have a lot of methods) you can use

为了节省一些键击（例如，如果接口有很多方法），您可以使用

abstract class Aggregate implements A,B{
}

new MyObject extends Aggregate{
   void foo(){}
   void bar(){}
}

Notice the key is to declare the Aggregate as abstract

请注意，关键是将Aggregate声明为抽象

#4

Note that you can make a named local class that implement the two interfaces:

请注意，您可以创建一个实现两个接口的命名本地类：

void method() {
    class Aggregate implements A, B {
        void foo() {}
        void bar() {}
    }

    A a = new Aggregate();
    B b = new Aggregate();
}

This save you from doing a class-level or top-level class declaration.

这使您无法进行类级别或*类声明。

The result is called a local class. Local classes declared in instance methods are also inner classes, which means that they can reference the containing object instance.

结果称为本地类。在实例方法中声明的本地类也是内部类，这意味着它们可以引用包含对象实例。

#1

#2