这是书上第11章持有对象里面的练习31题
(3)修改RandomShapeGenerator.java,使其成为一个Iterable。
这是LZ写的代码:
public class RandomShapeIterable implements Iterator<Shape> {
private Random rand = new Random(27);
private final int generateShapeNum;
public RandomShapeIterable( int generateShapeNum ) {
this.generateShapeNum = generateShapeNum;
}
public Iterator<Shape> iterator() {
return new Iterator<Shape>() {
private int num = 0;
public boolean hasNext() {
return num < generateShapeNum;
}
public Shape next() {
num++;
switch(rand.nextInt(3)) {
default:
case 0: return new Circle();
case 1: return new Square();
case 2: return new Triangle();
}
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public static void main(String[] args) {
for (Shape s : new RandomShapeIterable(10)) {
s.draw();
s.erase();
}
}}
报错如下:
在下面是答案上的代码
class RandomShapeGenerator implements Iterable<Shape> {
private Random rand = new Random(47);
private final int quantity; RandomShapeGenerator(int quantity) {
this.quantity = quantity;
} public Iterator<Shape> iterator() {
return new Iterator<Shape>() {
private int count; public boolean hasNext() {
return count < quantity;
} public Shape next() {
++count;
return nextShape();
} public void remove() { // Not implemented
throw new UnsupportedOperationException();
}
};
} private Shape nextShape() {
switch (rand.nextInt(3)) {
default:
case 0:
return new Circle();
case 1:
return new Square();
case 2:
return new Triangle();
}
}
}public class E31_IterableRandomShapeGenerator {
public static void main(String[] args) {
RandomShapeGenerator rsg = new RandomShapeGenerator(10);
for (Shape shape : rsg)
System.out.println(shape.getClass().getSimpleName());
}
}
好吧,撸主不明白的地方有两处:
一、为什么实现Iterable接口的类不用在类中实现hasNext()、next()、remove()的定义,
然而在内部类里实现后却能够运行?
二、撸主检查了一遍又一遍实在是找不到自己写的代码到底哪里出了错,我感觉明明就跟答案里的一样啊?
跪求大神指点啊!!!
(3)修改RandomShapeGenerator.java,使其成为一个Iterable。
这是LZ写的代码:
public class RandomShapeIterable implements Iterator<Shape> {
private Random rand = new Random(27);
private final int generateShapeNum;
public RandomShapeIterable( int generateShapeNum ) {
this.generateShapeNum = generateShapeNum;
}
public Iterator<Shape> iterator() {
return new Iterator<Shape>() {
private int num = 0;
public boolean hasNext() {
return num < generateShapeNum;
}
public Shape next() {
num++;
switch(rand.nextInt(3)) {
default:
case 0: return new Circle();
case 1: return new Square();
case 2: return new Triangle();
}
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public static void main(String[] args) {
for (Shape s : new RandomShapeIterable(10)) {
s.draw();
s.erase();
}
}}
报错如下:
在下面是答案上的代码
class RandomShapeGenerator implements Iterable<Shape> {
private Random rand = new Random(47);
private final int quantity; RandomShapeGenerator(int quantity) {
this.quantity = quantity;
} public Iterator<Shape> iterator() {
return new Iterator<Shape>() {
private int count; public boolean hasNext() {
return count < quantity;
} public Shape next() {
++count;
return nextShape();
} public void remove() { // Not implemented
throw new UnsupportedOperationException();
}
};
} private Shape nextShape() {
switch (rand.nextInt(3)) {
default:
case 0:
return new Circle();
case 1:
return new Square();
case 2:
return new Triangle();
}
}
}public class E31_IterableRandomShapeGenerator {
public static void main(String[] args) {
RandomShapeGenerator rsg = new RandomShapeGenerator(10);
for (Shape shape : rsg)
System.out.println(shape.getClass().getSimpleName());
}
}
好吧,撸主不明白的地方有两处:
一、为什么实现Iterable接口的类不用在类中实现hasNext()、next()、remove()的定义,
然而在内部类里实现后却能够运行?
二、撸主检查了一遍又一遍实在是找不到自己写的代码到底哪里出了错,我感觉明明就跟答案里的一样啊?
跪求大神指点啊!!!
答案是java.lang.Iterable,而楼主java.util.Iterator.
答案实现了那个接口的唯一的方法,而楼主没有实现那个接口的3个方法。
感谢啊,原来是这个问题!不过大神能回答我一下第一个问题么,为什么在类中没有
定义那三个方法,而在内部类定义却可以运行呢?按理说Iterable这个接口也需要实现三个方法啊
刚把代码改了一下,测试正常。
import java.util.*;
import static tij.util.Print.*;//静态引入,环境不同要变。
public class RandomShapeIterable implements Iterator<Shape>
{
private Random rand = new Random(27);
private final int generateShapeNum;
public RandomShapeIterable( int generateShapeNum )
{
this.generateShapeNum = generateShapeNum;
}
private int num = 0;
public boolean hasNext()
{
return num < generateShapeNum;
}
public Shape next()
{
num++;
switch(rand.nextInt(3))
{
default:
case 0: return new Circle();
case 1: return new Square();
case 2: return new Triangle();
}
}
public void remove()
{
throw new UnsupportedOperationException();
}
public static void main(String[] args)
{
RandomShapeIterable rsi=new RandomShapeIterable(10);
Shape s=null;
while(rsi.hasNext())
{
s=rsi.next();
s.draw();
s.erase();
}
}
}
class Shape
{
public void draw() {}
public void erase() {}
}
class Circle extends Shape
{
public void draw() { print("Circle.draw()"); }
public void erase() { print("Circle.erase()"); }
}
class Square extends Shape
{
public void draw() { print("Square.draw()"); }
public void erase() { print("Square.erase()"); }
}
class Triangle extends Shape
{
public void draw() { print("Triangle.draw()"); }
public void erase() { print("Triangle.erase()"); }
}
但输出的时候,因为没有实现Iterable接口,不可用foreach()循环,楼主可以自己改一下代码试试。