Java设计模式七大原则-开放-关闭原则

// 基础类
public class Shape {
    private String type;
    public Shape(String type) {
        this.type = type;
    }
    public void draw() {
        if (type.equals("Rectangle")) {
            System.out.println("三角形");
        } else if (type.equals("Circle")) {
            System.out.println("矩形");
        }
    }
}
// 客户端代码
public class Client {
    public static void main(String[] args) {
        Shape rectangle = new Shape("Rectangle");
        Shape circle = new Shape("Circle");
        rectangle.draw();
        circle.draw();
    }
}

// 抽象基础类
public abstract class Shape {
    public abstract void draw();
}
// 具体的Rectangle类
public class Rectangle extends Shape {
    @Override
    public void draw() {
        System.out.println("这是一个三角形");
    }
}
// 具体的Circle类
public class Circle extends Shape {
    @Override
    public void draw() {
        System.out.println("这是一个矩形");
    }
}
// 绘图工具类
public class DrawingTool {
    public static void drawShapes(List<Shape> shapes) {
        for (Shape shape : shapes) {
            shape.draw();
        }
    }
}
// 客户端代码
public class Client {
    public static void main(String[] args) {
        List<Shape> shapes = new ArrayList<>();
        shapes.add(new Rectangle());
        shapes.add(new Circle());
        DrawingTool.drawShapes(shapes);
    }
}