java - 在 Java 类中实现的具有相同方法签名的两个接口(interface)

Question

我有两个 Java 接口(interface)和一个实现类。

(我已经使用 Eclipse 直接运行该程序，并且我没有尝试通过从命令行显式编译来检查任何编译器警告等。)

为什么他们运行没有问题？为什么 Java 允许这样做，即使它满足两个接口(interface)的“契约”但在实现类时产生歧义？

更新了示例。

public interface CassettePlayer {
    void play();
}

public interface DVDPlayer {
    void play();
}

public class CarPlayer implements CassettePlayer,DVDPlayer{

    @Override
    public void play() {
        System.out.println("This plays DVD, screw you Cassette !");
    }

    public static void main(String args[]) {
        CarPlayer cp = new CarPlayer();
        cp.play();

        CassettePlayer firstInterface = new CarPlayer();
        firstInterface.play();

        DVDPlayer secondInterface = new CarPlayer();
        secondInterface.play();
    }
}

Answer 1

此场景在 Java Language Specification, section 8.1.5 中特别允许:

It is permitted for a single method declaration in a class to implement methods of more than one superinterface. For example, in the code:

interface Fish { int getNumberOfScales(); }
interface Piano { int getNumberOfScales(); }
class Tuna implements Fish, Piano {
   // You can tune a piano, but can you tuna fish?
   int getNumberOfScales() { return 91; }
}

the method getNumberOfScales in class Tuna has a name, signature, and return type that matches the method declared in interface Fish and also matches the method declared in interface Piano; it is considered to implement both.

文本接着指出，如果方法签名具有不同的返回类型，例如 double 和 int，则无法在将产生相同的类和编译时错误。