Java定义Shape接口实现多态。 interface Shape{ void draw(); void erase(); } Circle类、Square类、Triangle类实现Shape，编写程序NewShapes.java，利用Random类实现随机9次调用不同图形类绘图。 定义Shape接口实现多态。 interface Shape{ void draw(); void erase(); } Circle类、Square类、Triangle类实现Shape，编写程序NewShapes.java，利用Random类实现随机9次调用不同图形类绘图。

下面是实现要求的代码：

import java.util.Random;

interface Shape {
    void draw();
    void erase();
}

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

class Square implements Shape {
    public void draw() {
        System.out.println("Drawing a square");
    }
    public void erase() {
        System.out.println("Erasing a square");
    }
}

class Triangle implements Shape {
    public void draw() {
        System.out.println("Drawing a triangle");
    }
    public void erase() {
        System.out.println("Erasing a triangle");
    }
}

public class NewShapes {
    public static void main(String[] args) {
        Shape[] shapes = new Shape[9];
        Random rand = new Random();
        for (int i = 0; i < shapes.length; i++) {
            int randNum = rand.nextInt(3);
            if (randNum == 0) {
                shapes[i] = new Circle();
            } else if (randNum == 1) {
                shapes[i] = new Square();
            } else {
                shapes[i] = new Triangle();
            }
        }

        for (int i = 0; i < shapes.length; i++) {
            shapes[i].draw();
            shapes[i].erase();
            System.out.println();
        }
    }
}

程序首先定义了一个Shape接口，其中包含draw()和erase()两个方法。然后Circle、Square、Triangle三个类分别实现了Shape接口，并实现了接口中的两个方法。最后NewShapes类利用Random类随机生成9个不同的Shape对象，然后依次调用每个对象的draw()和erase()方法。

程序的输出结果类似于下面这样：

Drawing a triangle
Erasing a triangle

Drawing a circle
Erasing a circle

Drawing a square
Erasing a square

Drawing a triangle
Erasing a triangle

Drawing a square
Erasing a square

Drawing a circle
Erasing a circle

Drawing a square
Erasing a square

Drawing a square
Erasing a square

Drawing a triangle
Erasing a triangle

可以看到，程序随机生成了三种形状的对象，并依次调用它们的draw()和erase()方法。这就是Java中多态的一种体现。