11章-练习31

import com.example.demo.shape.RandomShapeGenerator;

import com.example.demo.shape.Shape;

import java.util.Iterator;

/**
 * 练习31：修改polymorphism/shape/RandomShapeGenerator.java,使其称为一个Iterable。
 * 你需要添加一个接收元素数量为参数的构造器，这个数量是指在停止之前，你想用迭代器生成的元素额数量。
 * 验证这个程序可以工作
 */

public class Exercise31 {

    public static void main(String[] args) {
        RandomShapeGenerator generator = new RandomShapeGenerator(8);
        for (Shape o : generator) {
            o.draw();
        }
    }
}

//: polymorphism/shape/RandomShapeGenerator.java
// A "factory" that randomly creates shapes.
package com.example.demo.shape;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.Random;

public class RandomShapeGenerator implements Iterable<Shape>{

    private Iterator<Shape> iterator;

    public RandomShapeGenerator(int size) {
        Shape[] shapes = new Shape[size];
        for (int i = 0; i < size; i++) {
            shapes[i] = next();
        }
        this.iterator = new ArrayList<Shape>(java.util.Arrays.asList(shapes)).iterator();
    }

    private Random rand = new Random(47);

    public Shape next() {
        switch (rand.nextInt(4)) {
            default:
            case 1:
                return new Circle();
            case 2:
                return new Square();
            case 3:
                return new Triangle();
        }
    }


    @Override
    public Iterator iterator() {
        return iterator;
    }
} ///:~