这篇博客探讨了Java编程中关于Command类的设计，包括实现一个包含String域和operation()方法的Command类，以及如何使用Command对象填充Queue并在不同类间交互。此外，还涉及PriorityQueue的使用，如填充Double值并进行排序。文章中还提到一些编程挑战，如使类适应Collection接口和实现Iterable接口，以及添加reversed()和randomized()方法。作者鼓励读者尝试这些练习，并提供了联系方式以解答疑问。
这是第十一章最后一节，之后我会做前11章节的回顾（按着目录捋）
题目27-32，其中30-32因为我没有源代码，所以我贴的官网答案。
编译器：IDEA
27.写一个称为Command的类，它包含一个String域和一个显示该String的operation()方法。写第二类，它具有一个使用Command对象来填充一个Queue并返回这个对象的方法。将填充后的Queue传递给第三个类的一个方法，该方法消耗掉Queue中的对象，并调用它们的operation()方法。
package job;
import java.lang.reflect.Array;
import java.util.*;
import java.util.Map.Entry;
class Command{
String a;
public void Operation(){
System.out.println(a);
}
}
class A {
public Queue<Command> a = new LinkedList<>(
Arrays.asList(new Command(), new Command())
);
}
class B {
void removea(Queue<Command> a){
for(Command b:a){
b.Operation();
System.out.println(a.remove());
}
}
}
public class Main {
public static void main(String[] args) {
A a=new A();
B b=new B();
b.removea(a.a);
}
}28.用由java.util.Random创建的Double值填充一个PriorityQueue（用offer()）方法，然后使用poll()移除并显示它们。
package job;
import java.lang.reflect.Array;
import java.util.*;
import java.util.Map.Entry;
public class Main {
public static void main(String[] args) {
Random rand=new Random();
PriorityQueue<Double>a=new PriorityQueue<>();
a.offer(rand.nextDouble());
a.offer(rand.nextDouble());
while (a.peek()!=null)
System.out.println(a.poll()+" ");
}
}29.创建一个继承自Object的简单类，它不包含任何成员，展示你不能将这个类的多个示例成功地添加到一个PriorityQueue中。这个问题将在第17章中详细解释。
package job;
import java.lang.reflect.Array;
import java.util.*;
class A extends Object{
}
public class Main {
public static void main(String[] args) {
PriorityQueue<A>a=new PriorityQueue<>();
a.offer(new A());
a.offer(new A());
}
}报错！
30.修改CollectionSequeuece.java，使其不要继承AbstractCollection，而是实现Collection。
//: holding/CollectionSequence.java
import typeinfo.pets.*;
import java.util.*;
class InterfaceVsIterator {
public static void display(Iterator<Pet> it) {
while(it.hasNext()) {
Pet p = it.next();
System.out.print(p.id() + ":" + p + " ");
}
System.out.println();
}
public static void display(Collection<Pet> pets) {
for(Pet p : pets)
System.out.print(p.id() + ":" + p + " ");
System.out.println();
}
}
public class Ja11_12_30
implements Collection<Pet> {
private Pet[] pets = Pets.createArray(8);
public int size() { return pets.length; }
public Iterator<Pet> iterator() {
return new Iterator<Pet>() {
private int index = 0;
public boolean hasNext() {
return index < pets.length;
}
public Pet next() { return pets[index++]; }
public void remove() { // Not implemented
throw new UnsupportedOperationException();
}
};
}
public boolean add(Pet p){throw new UnsupportedOperationException();}
public boolean addAll(Collection<? extends Pet> c){throw new UnsupportedOperationException();}
public void clear() {
if(this.size() != 0)
for(Pet p : pets)
p = null;
}
public boolean retainAll(Collection<?> c) {
throw new UnsupportedOperationException();
}
public boolean removeAll(Collection<?> c) {
throw new UnsupportedOperationException();
}
public boolean contains(Object o) {
throw new UnsupportedOperationException();
}
public boolean isEmpty() {
return (this.size() == 0) ? true : false;
}
public boolean containsAll(Collection<?> c) {
throw new UnsupportedOperationException();
}
public boolean remove(Object o) {
throw new UnsupportedOperationException();
}
public Object[] toArray() {
return pets;
}
public <T> T[] toArray(T[] a) {
throw new UnsupportedOperationException();
}
public static void main(String[] args) {
Ja11_12_30 c = new Ja11_12_30();
InterfaceVsIterator.display(c);
InterfaceVsIterator.display(c.iterator());
}
} /* Output:
*///:~
31.修改polymorphism/shape/RandomShapeGenerator.java，使其成为一个Iterable。你需要添加一个接受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的数量。验证这个程序可以工作。
/* Modify polymorphism/shape/RandomShapeGenerator.java to make it
* Iterable. You'll need to add a constructor that takes the number of
* elements that you want the iterator to produce before stopping. Verify
* that it works.
*/
import java.util.*;
import static net.mindview.util.Print.*;
class RandomShapeGenerator implements Iterable<Shape>{
private Random rand = new Random(47);
Shape[] shape;
RandomShapeGenerator(int count){
shape=new Shape[count];
for(int i=0;i<shape.length;i++)shape[i]=next();
}
public Shape next() {
switch(rand.nextInt(3)) {
default:
case 0: return new Circle();
case 1: return new Square();
case 2: return new Triangle();
}
}
public Iterator<Shape> iterator(){
return new Iterator<Shape>(){
private int index=-1;
public boolean hasNext(){return index<shape.length;}
public Shape next(){index++;return shape[index];}
public void remove(){throw new UnsupportedOperationException();}
};
}
}
public class Ja11_13_31{
public static void main(String[] args){
RandomShapeGenerator rs=new RandomShapeGenerator(4);
Iterator<Shape> it=rs.iterator();
while(it.hasNext()){
print(it.next());
it.remove();
}
}
}
32.按照MultiIterableClass示例，在NonCollectionSequence.java中添加reversed()和randomized()方法，并让NonCollectionSequence实现Iterable。然后在foreach语句中展示所有的使用方式。
/* Following the example of MultiIterableClass, add reversed() and randomized()
* methods to NonCollectionSequence.java, as well as making NonCollectionSequence.java
* implement Iterable and show that all the approaches * work in foreach statements.
*/
import java.util.*;
import static net.mindview.util.Print.*;
import typeinfo.pets.*;
class PetSequence {
protected Pet[] pets = Pets.createArray(8);
}
public class Ja11_13_32 extends PetSequence /*implements Iterable<Pet>*/ {
public Iterable<Pet> iterator(){
return new Iterable<Pet>(){
public Iterator<Pet> iterator() {
return new Iterator<Pet>() {
private int index = 0;
public boolean hasNext() {
return index<pets.length;
}
public Pet next() { return pets[index++]; }
public void remove() { // Not implemented
throw new UnsupportedOperationException();
}
};
}
};
}
public Iterable<Pet> reversed(){
return new Iterable<Pet>(){
public Iterator<Pet> iterator() {
return new Iterator<Pet>() {
private int index = pets.length-1;
public boolean hasNext() {
return index>-1;
}
public Pet next() { return pets[index--]; }
public void remove() { // Not implemented
throw new UnsupportedOperationException();
}
};
}
};
}
public Iterable<Pet> randomized(){
return new Iterable<Pet>(){
public Iterator<Pet> iterator(){
Random rand=new Random(6);
List<Pet> lp=new ArrayList<Pet>(Arrays.asList(pets));
Collections.shuffle(lp,rand);
return lp.iterator();
}
};
}
public static void display(Iterable<Pet> itb){
for(Pet i:itb){print(i);}
}
public static void main(String[] args) {
Ja11_13_32 nc = new Ja11_13_32();
display(nc.randomized());
print();
display(nc.iterator());
print();
display(nc.reversed());
}
}
/*Pug
Rat
Manx
Pug
Mutt
Cymric
Manx
Cymric
Rat
Manx
Cymric
Mutt
Pug
Cymric
Pug
Manx
Manx
Pug
Cymric
Pug
Mutt
Cymric
Manx
Rat*/
结束~
我的另一个博客：https://www.cnblogs.com/hsjj/
会不定时的更新算法题
有问题欢迎发送邮件至hpzhangjunjiell@163.com
我们下次见哦~
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