lambda表达式可以替代多态吗？

Question

我正在学习lambda表达式和功能接口.我们可以通过lambda表达式直接编写接口的实现.所以我认为,它可能是多态性的替代品.

我有一些使用多态的代码,

interface Drawable {
    public void draw();
}


class Shape {

    protected String name;

    public Shape(String name) {
        this.name = name;
    }
}

class Rectangle extends Shape implements Drawable  {

    public Rectangle(String name) {
        super(name);
    }

    @Override
    public void draw() {
        System.out.println("I am "+this.name);
        System.out.println("Drawing rectangle with 2 equal sides.");
    }
}

class Square extends Shape implements Drawable {

    public Square(String name) {
        super(name);
    }

    @Override
    public void draw() {
        System.out.println("I am "+this.name);
        System.out.println("Drawing square with 4 equal sides.");
    }
}


public class DrawShape {

    public static void main(String ar[]) {

        Drawable rectangle = new Rectangle("Rectangle");
        rectangle.draw();

        Drawable square = new Square("Square");
        square.draw();

    }
}

我用lambda表达式和函数接口编写了上面的代码,

@FunctionalInterface
interface Drawable {
    public void draw();
}


class Shape {
    private String name;
    public Shape(String name) {
        this.name = name;
    }

    public void draw(Drawable d1) {
        System.out.println("I am "+this.name);
        d1.draw();
    }
}



public class DrawShape {

    public static void main(String[] args) {
        Shape s1 = new Shape("Rectangle");
        Drawable rectangle = () -> System.out.println("Drawing rectangle with 2 equal sides.");
        s1.draw(rectangle);

        Shape s2 = new Shape("Square");
        Drawable sqaure = () -> System.out.println("Drawing square with 4 equal sides.");
        s2.draw(sqaure);
    }

}

哪种方法更好？那么lambda的代码可重用性,代码维护和修改,耦合和内聚等其他方面呢？

Answer 1

我认为lambda表达式允许开发人员编写完全多态的类型,就像全类实现一样.

多态性通常以两种方式出现:

Drawable drawable = new Rectangle("name");
drawable.draw();
Shape shape = (Shape) drawable; //same object, multiple types.

和:

Drawable drawable2 = new Rectangle("name");
drawable2.draw(); //Rectangle.draw() implementation invoked
drawable2 = new Square("name");
drawable2.draw(); //Square.draw() implementation

lambda表达式完全不允许这两个中的任何一个:

1. Lambda表达式仅用于实现功能接口.这是第一个主要限制.

2. 虽然可以这样做:

   Drawable drawable = () -> System.out.println("drawing rectangle");
   drawable = () -> System.out.println("drawing square");
   

   这不是严格相同的事情作为第二代码段以上(在一个更复杂的例子,人们将能够提供一种在基本实现Shape,并有它在重写Rectangle和Square;以及将不可能与lambda表达式).另外,一个人认为上面的两个赋值使用不同的源代码是正确的.

3. 人们不能像使用类一样"强制转换"类型:

   Drawable drawable3 = () -> System.out.println("Drawing something");
   Shape shape3 = (Shape) drawable3; //Class cast exception.
   

换句话说,lambda表达式非常适合函数式编程编码,而不是良好的面向对象设计的替代品.