接口方法返回类型是实现接口的类

public interface Shape {
    void draw();
}

public class Circle implements Shape {
    @Override
    public void draw() {
        System.out.println("Drawing a circle");
    }
}

public class Rectangle implements Shape {
    @Override
    public void draw() {
        System.out.println("Drawing a rectangle");
    }
}

public class Main {
    public static void main(String[] args) {
        Shape circle = new Circle();
        Shape rectangle = new Rectangle();
        
        circle.draw();      // 输出：Drawing a circle
        rectangle.draw();   // 输出：Drawing a rectangle
    }
}