classDiagram
    class calrect {
        <<interface>>
        + int calarea()
        + int calgirth()
        + int getx()
        + int gety()
    }

    class RRect {
        - int x
        - int y
        + RRect()
        + int calarea()
        + int calgirth()
        + int getx()
        + int gety()
    }

    class Class1 {
        + RRect rect
        + main(String[] args)
    }

    calrect <|.. RRect : 实现
    Class1 --> RRect : 创建与使用