Java接口代码错误

Question

我无法理解为什么我在下面指出的行上收到错误.如果有特定主题涵盖它,请提供一行(或解释).

public interface Button {
  void press();
}
public class Bomb implements Button {
  public void press() {
    System.out.println("Doesn't work");
  }
  void boom() {
    System.out.println("Exploded");
  }
}
public class Test {
  public static void main(String[] args) {
    Button redButton = new Bomb();
    redButton.press();
    redButton.boom(); // <-- Error is on this line.
  }
}

Answer 1

Button redButton = new Bomb();

接口Button未定义方法boom().

运行时实例可能是Bomb(有boom()),但编译器不知道(它只看到编译时类型,即Button).

您需要使用类定义的接口Bomb:

Bomb redButton = new Bomb();