在Java中用接口定义类的能力的实用方面？ [英] Practical side of the ability to define a class within an interface in Java?

问题描述

在Java中用接口定义类的能力的实际方面是什么：

What would be the practical side of the ability to define a class within an interface in Java:

interface IFoo
{
    class Bar
    {
        void foobar ()
        {
            System.out.println("foobaring...");
        }
    }
}

推荐答案

我可以想到另一种用法，而不是Eric P链接的用法：定义接口的默认/无操作实现。

I can think of another usage than those linked by Eric P: defining a default/no-op implementation of the interface.

./ alex

interface IEmployee
{

    void workHard ();  
    void procrastinate ();

    class DefaultEmployee implements IEmployee 
    {
        void workHard () { procrastinate(); };
        void procrastinate () {};
    }

}

又一个样本 - 实施< a href =http://en.wikipedia.org/wiki/Null_Object_pattern =nofollow noreferrer>空对象模式：

Yet another sample — implementation of Null Object Pattern:

interface IFoo
{
    void doFoo();
    IFoo NULL_FOO = new NullFoo();

    final class NullFoo implements IFoo
    {
        public void doFoo () {};
        private NullFoo ()  {};
    }
}


...
IFoo foo = IFoo.NULL_FOO;
...
bar.addFooListener (foo);
...

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