这个界面有什么问题？ [复制]

Question

接口可以包含正文吗？帮我解决这部分

public interface Figures
{
  public void printMessage (String s)
  {
    System.out.println ("This figure is " + s);
  }
  public double area ();    // to calculate the area of the figure
}

Answer 1

接口是一个完全“抽象的类”，用于将相关方法与空体进行分组

public interface Figures
{
  public void printMessage (String s);
  public double area ();    // to calculate the area of the figure
}

要访问接口方法，接口必须由另一个类使用 implements 关键字（而不是扩展）“实现”（有点像继承）。接口方法的主体由“实现”类提供。

here 解释清楚

这是w3school的例子

// Interface
interface Animal {
  public void animalSound(); // interface method (does not have a body)
  public void sleep(); // interface method (does not have a body)
}

// Pig "implements" the Animal interface
class Pig implements Animal {
  public void animalSound() {
    // The body of animalSound() is provided here
    System.out.println("The pig says: wee wee");
  }
  public void sleep() {
    // The body of sleep() is provided here
    System.out.println("Zzz");
  }
}

class Main {
  public static void main(String[] args) {
    Pig myPig = new Pig();  // Create a Pig object
    myPig.animalSound();
    myPig.sleep();
  }
}

Answer 2

从 Java 8 开始，我们可以使用 default 关键字为接口方法提供默认植入

public interface Figures
{
  public default void printMessage (String s)
  {
    System.out.println ("This figure is " + s);
  }
  public double area ();    // to calculate the area of the figure
}