默认和静态方法如何在Java 8接口中工作? [英] How do default and static methods work in java 8 interfaces?

问题描述

我一直在努力弄清默认和静态方法在Java 8中的实际工作方式是什么?

I have been trying to get my head around on how actually do the default and static methods work in java 8?

考虑以下界面:

public interface Car {

  default void drive() {
    System.out.println("Default Driving");
  }

  static int getWheelCount(){
    return wheelCount;
  }

  int wheelCount = 7;
}

和以下实现:

public class Benz implements Car { }

现在，如果我转到主方法并编写:

Now if I go to my main method and write:

public static void main(String[] args){
  Car car = new Benz();
  car.drive();
  System.out.println(Car.getWheelCount());
  System.out.println(Car.wheelCount);
}

我想知道引擎盖下到底发生了什么事

I would like to know what is really going on under the hood:

1. 是否以类似于抽象类工作方式的方式在Car实例上调用默认方法?
2. 为了在接口中支持默认和静态方法，该语言需要哪些新功能/修改?
3. 我知道默认情况下，界面中的所有字段默认情况下都是public static final，无论如何与我上面的问题有关.
4. 通过引入默认方法，我们是否不再需要抽象类?

1. Does the default method get called upon the instance of Car in a way which is similar to how abstract classes work?
2. What new features/modifications did the language need in order to support default and static methods in interfaces?
3. I know that by default, all the fields in an interface are by default public static final, is that in any way related to my above questions.
4. With the introduction of default methods, do we have the need of abstract classes anymore?

PS
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P.S.
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推荐答案

1. 是.

1. Yes.

Java接口默认方法将帮助我们扩展接口，而不必担心会破坏实现类.

Java interface default methods will help us in extending interfaces without having the fear of breaking implementation classes.

如果那些由计算机控制的汽车制造商添加新产品怎么办 功能，例如飞往他们的汽车吗?这些制造商 需要指定新方法来启用其他公司(例如 电子制导仪器制造商)调整其软件 飞行汽车.这些汽车制造商将在哪里宣布这些新产品 与飞行有关的方法?如果他们将它们添加到原始界面中， 那么实现了这些接口的程序员将不得不 重写其实现.如果他们将其添加为静态方法， 然后程序员会将它们视为实用程序方法，而不是 必不可少的核心方法.

What if those computer-controlled car manufacturers add new functionality, such as flight, to their cars? These manufacturers would need to specify new methods to enable other companies (such as electronic guidance instrument manufacturers) to adapt their software to flying cars. Where would these car manufacturers declare these new flight-related methods? If they add them to their original interfaces, then programmers who have implemented those interfaces would have to rewrite their implementations. If they add them as static methods, then programmers would regard them as utility methods, not as essential, core methods.

不需要覆盖

1. AFAIK，静态方法，因此静态方法的final是连贯的.覆盖取决于拥有类的实例. 静态方法与类的任何实例都不关联，因此该概念不适用.但是，默认方法必须具有上面我引用的可重写属性.

1. AFAIK, static methods aren't needed to override, so being final of static methods is coherent. Overriding depends on having an instance of a class. A static method is not associated with any instance of a class so the concept is not applicable. However, default methods must have overrideable property as I quote above.

您可以在Java 8的界面中使用默认的ctor，私有字段，实例成员吗?

---

我喜欢使用默认方法，

---

I like to use thanks to default methods,

list.sort(ordering);

代替

Collections.sort(list, ordering);

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