Java2实用教程2（第五版）耿祥义课后习题参考答案

2．有4种原因的中断：（1）JVM将CPU资源从当前线程切换给其他线程，使本线程让出CPU的使用权处于中断状态。（2）线程使用CPU资源期间，执行了sleep(int millsecond)方法，使当前线程进入休眠状态。（3）线程使用CPU资源期间，执行了wait()方法，使得当前线程进入等待状态。（4）线程使用CPU资源期间，执行某个操作进入阻塞状态，比如执行读/写操作引起阻塞。

3．死亡状态，不能再调用start()方法。

4．新建和死亡状态。

5．两种方法：用Thread类或其子类。

6．使用 setPrority(int grade)方法。

7．Java使我们可以创建多个线程，在处理多线程问题时，我们必须注意这样一个问题：当两个或多个线程同时访问同一个变量，并且一个线程需要修改这个变量。我们应对这样的问题作出处理，否则可能发生混乱。

8．当一个线程使用的同步方法中用到某个变量，而此变量又需要其它线程修改后才能符合本线程的需要，那么可以在同步方法中使用wait()方法。使用wait方法可以中断方法的执行，使本线程等待，暂时让出CPU的使用权，并允许其它线程使用这个同步方法。其它线程如果在使用这个同步方法时不需要等待，那么它使用完这个同步方法的同时，应当用notifyAll()方法通知所有的由于使用这个同步方法而处于等待的线程结束等待。

9．不合理。

10．“吵醒”休眠的线程。一个占有CPU资源的线程可以让休眠的线程调用interrupt 方法“吵醒”自己，即导致休眠的线程发生InterruptedException异常，从而结束休眠，重新排队等待CPU资源。

二、选择题

1．A。2．A。3．B。

三、阅读程序

1．属于上机调试题目，解答略。

2．属于上机调试题目，解答略。

3．属于上机调试题目，解答略。

4．属于上机调试题目，解答略。

5．属于上机调试题目，解答略。

6．属于上机调试题目，解答略

7．【代码】：BA。

8．属于上机调试题目，解答略

四、编写程序

1. public class E {

public static void main(String args[]) {

Cinema a=new Cinema();

a.zhang.start();

a.sun.start();

a.zhao.start();

}

class TicketSeller //负责卖票的类。

{ int fiveNumber=3,tenNumber=0,twentyNumber=0;

public synchronized void sellTicket(int receiveMoney)

{ if(receiveMoney==5)

{ fiveNumber=fiveNumber+1;

System.out.println(Thread.currentThread().getName()+

"给我5元钱，这是您的1张入场卷");

}

else if(receiveMoney==10)

{ while(fiveNumber<1)

{ try { System.out.println(Thread.currentThread().getName()+"靠边等");

wait();

System.out.println(Thread.currentThread().getName()+"结束等待");

}

catch(InterruptedException e) {}

}

fiveNumber=fiveNumber-1;

tenNumber=tenNumber+1;

System.out.println(Thread.currentThread().getName()+

"给我10元钱,找您5元,这是您的1张入场卷");

}

else if(receiveMoney==20)

{ while(fiveNumber<1||tenNumber<1)

{ try { System.out.println(Thread.currentThread().getName()+"靠边等");

wait();

System.out.println(Thread.currentThread().getName()+"结束等待");

}

catch(InterruptedException e) {}

}

fiveNumber=fiveNumber-1;

tenNumber=tenNumber-1;

twentyNumber=twentyNumber+1;

System.out.println(Thread.currentThread().getName()+

"给20元钱，找您一张5元和一张10元，这是您的1张入场卷");

}

notifyAll();

}

class Cinema implements Runnable

{ Thread zhang,sun,zhao;

TicketSeller seller;

Cinema()

{ zhang=new Thread(this);

sun=new Thread(this);

zhao=new Thread(this);

zhang.setName("张小有");

sun.setName("孙大名");

zhao.setName("赵中堂");

seller=new TicketSeller();

}

public void run()

{ if(Thread.currentThread()==zhang)

{ seller.sellTicket(20);

}

else if(Thread.currentThread()==sun)

{ seller.sellTicket(10);

}

else if(Thread.currentThread()==zhao)

{ seller.sellTicket(5);

}

2. 参照本章例子6

3．参照本章例子9

习题十三（第13章）

一、问答题

1．一个URL对象通常包含最基本的三部分信息：协议、地址、资源。

2．URL对象调用InputStream openStream() 方法可以返回一个输入流，该输入流指向URL对象所包含的资源。通过该输入流可以将服务器上的资源信息读入到客户端。

3．客户端的套接字和服务器端的套接字通过输入、输出流互相连接后进行通信。

4．使用方法accept()，accept()会返回一个和客户端Socket对象相连接的Socket对象。accept方法会堵塞线程的继续执行，直到接收到客户的呼叫。。

5．域名/IP。

四、编程题

1. （1）客户端

import java.net.*;

import java.io.*;

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class Client

{ public static void main(String args[])

{ new ComputerClient();

}

class ComputerClient extends Frame implements Runnable,ActionListener

{ Button connection,send;

TextField inputText,showResult;

Socket socket=null;

DataInputStream in=null;

DataOutputStream out=null;

Thread thread;

ComputerClient()

{ socket=new Socket();

setLayout(new FlowLayout());

Box box=Box.createVerticalBox();

connection=new Button("连接服务器");

send=new Button("发送");

send.setEnabled(false);

inputText=new TextField(12);

showResult=new TextField(12);

box.add(connection);

box.add(new Label("输入三角形三边的长度,用逗号或空格分隔:"));

box.add(inputText);

box.add(send);

box.add(new Label("收到的结果："));

box.add(showResult);

connection.addActionListener(this);

send.addActionListener(this);

thread=new Thread(this);

add(box);

setBounds(10,30,300,400);

setVisible(true);

validate();

addWindowListener(new WindowAdapter()

{ public void windowClosing(WindowEvent e)

{ System.exit(0);

}

});

}

public void actionPerformed(ActionEvent e)

{ if(e.getSource()==connection)

{ try //请求和服务器建立套接字连接：

{ if(socket.isConnected())

{}

else

{ InetAddress address=InetAddress.getByName("127.0.0.1");

InetSocketAddress socketAddress=new InetSocketAddress(address,4331);

socket.connect(socketAddress);

in =new DataInputStream(socket.getInputStream());

out = new DataOutputStream(socket.getOutputStream());

send.setEnabled(true);

thread.start();

}

catch (IOException ee){}

}

if(e.getSource()==send)

{ String s=inputText.getText();

if(s!=null)

{ try { out.writeUTF(s);

}

catch(IOException e1){}

}

public void run()

{ String s=null;

while(true)

{ try{ s=in.readUTF();

showResult.setText(s);

}

catch(IOException e)

{ showResult.setText("与服务器已断开");

break;

}

（2）服务器端

import java.io.*;

import java.net.*;

import java.util.*;

public class Server

{ public static void main(String args[])

{ ServerSocket server=null;

Server_thread thread;

Socket you=null;

while(true)

{ try{ server=new ServerSocket(4331);

}

catch(IOException e1)

{ System.out.println("正在监听"); //ServerSocket对象不能重复创建

}

try{ System.out.println(" 等待客户呼叫");

you=server.accept();

System.out.println("客户的地址:"+you.getInetAddress());

}

catch (IOException e)

{ System.out.println("正在等待客户");

}

if(you!=null)

{ new Server_thread(you).start(); //为每个客户启动一个专门的线程

}

class Server_thread extends Thread

{ Socket socket;

DataOutputStream out=null;

DataInputStream in=null;

String s=null;

boolean quesion=false;

Server_thread(Socket t)

{ socket=t;

try { out=new DataOutputStream(socket.getOutputStream());

in=new DataInputStream(socket.getInputStream());

}

catch (IOException e)

{}

}

public void run()

{ while(true)

{ double a[]=new double[3] ;

int i=0;

try{ s=in.readUTF();//堵塞状态，除非读取到信息

quesion=false;

StringTokenizer fenxi=new StringTokenizer(s," ,");

while(fenxi.hasMoreTokens())

{ String temp=fenxi.nextToken();

try{ a[i]=Double.valueOf(temp).doubleValue();i++;

}

catch(NumberFormatException e)

{ out.writeUTF("请输入数字字符");

quesion=true;

}

if(quesion==false)

{ double p=(a[0]+a[1]+a[2])/2.0;

out.writeUTF(" "+Math.sqrt(p*(p-a[0])*(p-a[1])*(p-a[2])));

}

catch (IOException e)

{ System.out.println("客户离开");

return;

}

2. 客户端Client.java

import java.net.*;

import java.io.*;

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class Client

{ public static void main(String args[])

{ new ChatClient();

}

class ChatClient extends Frame implements Runnable,ActionListener

{ Button connection,send;

TextField inputName,inputContent;

TextArea chatResult;

Socket socket=null;

DataInputStream in=null;

DataOutputStream out=null;

Thread thread;

String name="";

public ChatClient ()

{ socket=new Socket();

Box box1=Box.createHorizontalBox();

connection=new Button("连接服务器");

send=new Button("发送");

send.setEnabled(false);

inputName=new TextField(6);

inputContent=new TextField(22);

chatResult=new TextArea();

box1.add(new Label("输入妮称:"));

box1.add(inputName);

box1.add(connection);

Box box2=Box.createHorizontalBox();

box2.add(new Label("输入聊天内容:"));

box2.add(inputContent);

box2.add(send);

connection.addActionListener(this);

send.addActionListener(this);

thread=new Thread(this);

add(box1,BorderLayout.NORTH);

add(box2,BorderLayout.SOUTH);

add(chatResult,BorderLayout.CENTER);

setBounds(10,30,400,280);

setVisible(true);

validate();

addWindowListener(new WindowAdapter()

{ public void windowClosing(WindowEvent e)

{ System.exit(0);

}

});

}

public void actionPerformed(ActionEvent e)

{ if(e.getSource()==connection)

{ try

{ if(socket.isConnected())

{}

else

{ InetAddress address=InetAddress.getByName("127.0.0.1");

InetSocketAddress socketAddress=new InetSocketAddress(address,666);

socket.connect(socketAddress);

in =new DataInputStream(socket.getInputStream());

out = new DataOutputStream(socket.getOutputStream());

name=inputName.getText();

out.writeUTF("姓名:"+name);

send.setEnabled(true);

if(!(thread.isAlive()))

thread=new Thread(this);

thread.start();

}

catch (IOException ee){}

}

if(e.getSource()==send)

{ String s=inputContent.getText();

if(s!=null)

{ try { out.writeUTF("聊天内容:"+name+":"+s);

}

catch(IOException e1){}

}

public void run()

{ String s=null;

while(true)

{ try{ s=in.readUTF();

chatResult.append("\n"+s);

}

catch(IOException e)

{ chatResult.setText("与服务器已断开");

try { socket.close();

}

catch(Exception exp) {}

break;

}

服务器端ChatServer.java

import java.io.*;

import java.net.*;

import java.util.*;

public class ChatServer

{ public static void main(String args[])

{ ServerSocket server=null;

Socket you=null;

Hashtable peopleList;

peopleList=new Hashtable();

while(true)

{ try { server=new ServerSocket(666);

}

catch(IOException e1)

{ System.out.println("正在监听");

}

try { you=server.accept();

InetAddress address=you.getInetAddress();

System.out.println("客户的IP:"+address);

}

catch (IOException e) {}

if(you!=null)

{ Server_thread peopleThread=new Server_thread(you,peopleList);

peopleThread.start();

}

else { continue;

}

class Server_thread extends Thread

{ String name=null;

Socket socket=null;

File file=null;

DataOutputStream out=null;

DataInputStream in=null;

Hashtable peopleList=null;

Server_thread(Socket t,Hashtable list)

{ peopleList=list;

socket=t;

try { in=new DataInputStream(socket.getInputStream());

out=new DataOutputStream(socket.getOutputStream());

}

catch (IOException e) {}

}

public void run()

{ while(true)

{ String s=null;

try{

s=in.readUTF();

if(s.startsWith("姓名:"))

{ name=s;

boolean boo=peopleList.containsKey(name);

if(boo==false)

{ peopleList.put(name,this);

}

else

{ out.writeUTF("请换妮称:");

socket.close();

break;

}

else if(s.startsWith("聊天内容"))

{ String message=s.substring(s.indexOf(":")+1);

Enumeration chatPersonList=peopleList.elements();

while(chatPersonList.hasMoreElements())

{ ((Server_thread)chatPersonList.nextElement()).out.writeUTF("聊天内容:"+

message);

}

catch(IOException ee)

{ Enumeration chatPersonList=peopleList.elements();

while(chatPersonList.hasMoreElements())

{ try

{ Server_thread th=(Server_thread)chatPersonList.nextElement();

if(th!=this&&th.isAlive())

{ th.out.writeUTF("客户离线:"+name);

}

catch(IOException eee){}

}

peopleList.remove(name);

try { socket.close();

}

catch(IOException eee){}

System.out.println(name+"客户离开了");

break;

}

3．BroadCastWord.java

import java.io.*;

import java.net.*;

import java.awt.*;

import java.awt.event.*;

import javax.swing.Timer;

public class BroadCastWord extends Frame implements ActionListener

{ int port;

InetAddress group=null;

MulticastSocket socket=null;

Timer time=null;

FileDialog open=null;

Button select,开始广播,停止广播;

File file=null;

String FileDir=null,fileName=null;

FileReader in=null;

BufferedReader bufferIn=null;

int token=0;

TextArea 显示正在播放内容,显示已播放的内容;

public BroadCastWord()

{ super("单词广播系统");

select=new Button("选择要广播的文件");

开始广播=new Button("开始广播");

停止广播=new Button("停止广播");

select.addActionListener(this);

开始广播.addActionListener(this);

停止广播.addActionListener(this);

time=new Timer(2000,this);

open=new FileDialog(this,"选择要广播的文件",FileDialog.LOAD);

显示正在播放内容=new TextArea(10,10);

显示正在播放内容.setForeground(Color.blue);

显示已播放的内容=new TextArea(10,10);

Panel north=new Panel();

north.add(select);

north.add(开始广播);

north.add(停止广播);

add(north,BorderLayout.NORTH);

Panel center=new Panel();

center.setLayout(new GridLayout(1,2));

center.add(显示正在播放内容);

center.add(显示已播放的内容);

add(center,BorderLayout.CENTER);

validate();

try

{ port=5000;

group=InetAddress.getByName("239.255.0.0");

socket=new MulticastSocket(port);

socket.setTimeToLive(1);

socket.joinGroup(group);

}

catch(Exception e)

{ System.out.println("Error: "+ e);

}

setBounds(100,50,360,380);

setVisible(true);

addWindowListener(new WindowAdapter()

{ public void windowClosing(WindowEvent e)

{ System.exit(0);

}

});

}

public void actionPerformed(ActionEvent e)

{ if(e.getSource()==select)

{显示已播放的内容.setText(null);

open.setVisible(true);

fileName=open.getFile();

FileDir=open.getDirectory();

if(fileName!=null)

{ time.stop();

file=new File(FileDir,fileName);

try

{ file=new File(FileDir,fileName);

in=new FileReader(file);

bufferIn=new BufferedReader(in);

}

catch(IOException ee) { }

}

else if(e.getSource()==开始广播)

{ time.start();

}

else if(e.getSource()==time)

{ String s=null;

try { if(token==-1)

{ file=new File(FileDir,fileName);

in=new FileReader(file);

bufferIn=new BufferedReader(in);

}

s=bufferIn.readLine();

if(s!=null)

{ token=0;

显示正在播放内容.setText("正在广播的内容:\n"+s);

显示已播放的内容.append(s+"\n");

DatagramPacket packet=null;

byte data[]=s.getBytes();

packet=new DatagramPacket(data,data.length,group,port);

socket.send(packet);

}

else

{ token=-1;

}

catch(IOException ee) { }

}

else if(e.getSource()==停止广播)

{ time.stop();

}

public static void main(String[] args)

{ BroadCastWord broad=new BroadCastWord();

}

Receive.java

import java.net.*;

import java.awt.*;

import java.awt.event.*;

public class Receive extends Frame implements Runnable,ActionListener

{ int port;

InetAddress group=null;

MulticastSocket socket=null;

Button 开始接收,停止接收;

TextArea 显示正在接收内容,显示已接收的内容;

Thread thread;

boolean 停止=false;

public Receive()

{ super("定时接收信息");

thread=new Thread(this);

开始接收=new Button("开始接收");

停止接收=new Button("停止接收");

停止接收.addActionListener(this);

开始接收.addActionListener(this);

显示正在接收内容=new TextArea(10,10);

显示正在接收内容.setForeground(Color.blue);

显示已接收的内容=new TextArea(10,10);

Panel north=new Panel();

north.add(开始接收);

north.add(停止接收);

add(north,BorderLayout.NORTH);

Panel center=new Panel();

center.setLayout(new GridLayout(1,2));

center.add(显示正在接收内容);

center.add(显示已接收的内容);

add(center,BorderLayout.CENTER);

validate();

port=5000;

try{ group=InetAddress.getByName("239.255.0.0");

socket=new MulticastSocket(port);

socket.joinGroup(group);

}

catch(Exception e) { }

setBounds(100,50,360,380);

setVisible(true);

addWindowListener(new WindowAdapter()

{ public void windowClosing(WindowEvent e)

{ System.exit(0);

}

});

}

public void actionPerformed(ActionEvent e)

{ if(e.getSource()==开始接收)

{ 开始接收.setBackground(Color.blue);

停止接收.setBackground(Color.gray);

if(!(thread.isAlive()))

{ thread=new Thread(this);

}

try { thread.start();

停止=false;

}

catch(Exception ee) { }

}

if(e.getSource()==停止接收)

{ 开始接收.setBackground(Color.gray);

停止接收.setBackground(Color.blue);

thread.interrupt();

停止=true;

}

public void run()

{ while(true)

{ byte data[]=new byte[8192];

DatagramPacket packet=null;

packet=new DatagramPacket(data,data.length,group,port);

try { socket.receive(packet);

String message=new String(packet.getData(),0,packet.getLength());

显示正在接收内容.setText("正在接收的内容:\n"+message);

显示已接收的内容.append(message+"\n");

}

catch(Exception e) { }

if(停止==true)

{ break;

}

public static void main(String args[])

{ new Receive();

}

习题十四（第14章）

一、问答题

1．2个参数。

2．6个参数。

3．7个参数。

4．（1）创建AffineTransform对象，（2）进行旋转操作，（3）绘制旋转的图形。

二、编写程序

1. import java.awt.*;

import javax.swing.*;

class MyCanvas extends Canvas {

static int pointX[]=new int[5],

pointY[]=new int[5];

public void paint(Graphics g) {

g.translate(200,200) ; //进行坐标变换,将新的坐标原点设置为(200,200)。

pointX[0]=0;

pointY[0]=-120;

double arcAngle=(72*Math.PI)/180;

for(int i=1;i<5;i++) {

pointX[i]=(int)(pointX[i-1]*Math.cos(arcAngle)-pointY[i-1]*Math.sin(arcAngle));

pointY[i]=(int)(pointY[i-1]*Math.cos(arcAngle)+pointX[i-1]*Math.sin(arcAngle));

}

g.setColor(Color.red);

int starX[]={pointX[0],pointX[2],pointX[4],pointX[1],pointX[3],pointX[0]};

int starY[]={pointY[0],pointY[2],pointY[4],pointY[1],pointY[3],pointY[0]};

g.drawPolygon(starX,starY,6);

}

public class E {

public static void main(String args[]) {

JFrame f=new JFrame();

f.setSize(500,450);

f.setVisible(true);

MyCanvas canvas=new MyCanvas();

f.add(canvas,"Center");

f.validate();

f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

}

2. import java.awt.*;

import javax.swing.*;

import java.awt.geom.*;

class MyCanvas extends Canvas {

public void paint(Graphics g) {

g.setColor(Color.red) ;

Graphics2D g_2d=(Graphics2D)g;

QuadCurve2D quadCurve=

new QuadCurve2D.Double(2,10,51,90,100,10);

g_2d.draw(quadCurve);

quadCurve.setCurve(2,100,51,10,100,100);

g_2d.draw(quadCurve);

}

public class E {

public static void main(String args[]) {

JFrame f=new JFrame();

f.setSize(500,450);

f.setVisible(true);

MyCanvas canvas=new MyCanvas();

f.add(canvas,"Center");

f.validate();

f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

}

3. import java.awt.*;

import javax.swing.*;

import java.awt.geom.*;

class MyCanvas extends Canvas {

public void paint(Graphics g) {

g.setColor(Color.red) ;

Graphics2D g_2d=(Graphics2D)g;

CubicCurve2D cubicCurve=

new CubicCurve2D.Double(0,70,70,140,140,0,210,70);

g_2d.draw(cubicCurve);

}

public class E {

public static void main(String args[]) {

JFrame f=new JFrame();

f.setSize(500,450);

f.setVisible(true);

MyCanvas canvas=new MyCanvas();

f.add(canvas,"Center");

f.validate();

f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

}

4. import java.awt.*;

import javax.swing.*;

import java.awt.geom.*;

class Flower extends Canvas

{ public void paint(Graphics g)

{ Graphics2D g_2d=(Graphics2D)g;

//花叶两边的曲线:

QuadCurve2D

curve_1=new QuadCurve2D.Double(200,200,150,160,200,100);

CubicCurve2D curve_2=

new CubicCurve2D.Double(200,200,260,145,190,120,200,100);

//花叶中的纹线:

Line2D line=new Line2D.Double(200,200,200,110);

QuadCurve2D leaf_line1=

new QuadCurve2D.Double(200,180,195,175,190,170);

QuadCurve2D leaf_line2=

new QuadCurve2D.Double(200,180,210,175,220,170);

QuadCurve2D leaf_line3=

new QuadCurve2D.Double(200,160,195,155,190,150);

QuadCurve2D leaf_line4=

new QuadCurve2D.Double(200,160,214,155,220,150);

//利用旋转来绘制花朵:

AffineTransform trans=new AffineTransform();

for(int i=0;i<6;i++)

{ trans.rotate(60*Math.PI/180,200,200);

g_2d.setTransform(trans);

GradientPaint gradient_1=

new GradientPaint(200,200,Color.green,200,100,Color.yellow);

g_2d.setPaint(gradient_1);

g_2d.fill(curve_1);

GradientPaint gradient_2=new

GradientPaint(200,145,Color.green,260,145,Color.red,true);

g_2d.setPaint(gradient_2);

g_2d.fill(curve_2);

Color c3=new Color(0,200,0); g_2d.setColor(c3);

g_2d.draw(line);

g_2d.draw(leaf_line1); g_2d.draw(leaf_line2);

g_2d.draw(leaf_line3); g_2d.draw(leaf_line4);

}

//花瓣中间的花蕾曲线:

QuadCurve2D center_curve_1=

new QuadCurve2D.Double(200,200,190,185,200,180);

AffineTransform trans_1=new AffineTransform();

for(int i=0;i<12;i++)

{ trans_1.rotate(30*Math.PI/180,200,200);

g_2d.setTransform(trans_1);

GradientPaint gradient_3=

new GradientPaint(200,200,Color.red,200,180,Color.yellow);

g_2d.setPaint(gradient_3);

g_2d.fill(center_curve_1);

}

public class E {

public static void main(String args[]) {

JFrame f=new JFrame();

f.setSize(500,450);

f.setVisible(true);

Flower canvas=new Flower();

f.add(canvas,"Center");

f.validate();

f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

}

5． import java.awt.*;

import javax.swing.*;

import java.awt.geom.*;

class Moon extends Canvas

{ public void paint(Graphics g)

{ Graphics2D g_2d=(Graphics2D)g;

Ellipse2D ellipse1=

new Ellipse2D. Double (20,80,60,60),

ellipse2=

new Ellipse2D. Double (40,80,80,80);

g_2d.setColor(Color.white);

Area a1=new Area(ellipse1),

a2=new Area(ellipse2);

a1.subtract(a2); //"差"

g_2d.fill(a1);

}

public class E {

public static void main(String args[]) {

JFrame f=new JFrame();

f.setSize(500,450);

f.setVisible(true);

Moon moon=new Moon();

moon.setBackground(Color.black);

f.add(moon,"Center");

f.validate();

f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

}

习题十五（第15章）

一、问答题

1．LinkedList使用链式存储结构，ArrayList使用顺序存储结构。

2．迭代器遍历在找到集合中的一个对象的同时，也得到待遍历的后继对象的引用，因此迭代器可以快速地遍历集合。

3．不是。

4．用HashMap<K,V>来存储。

二、阅读程序

1．8。

2．ABCD。

三、编写程序

1. import java.util.*;

public class E {

public static void main(String args[]) {

Stack<Integer> stack=new Stack<Integer>();

stack.push(new Integer(3));

stack.push(new Integer(8));

int k=1;

while(k<=10) {

for(int i=1;i<=2;i++) {

Integer F1=stack.pop();

int f1=F1.intValue();

Integer F2=stack.pop();

int f2=F2.intValue();

Integer temp=new Integer(2*f1+2*f2);

System.out.println(""+temp.toString());

stack.push(temp);

stack.push(F2);

k++;

}

2. import java.util.*;

class Student implements Comparable {

int english=0;

String name;

Student(int english,String name) {

this.name=name;

this.english=english;

}

public int compareTo(Object b) {

Student st=(Student)b;

return (this.english-st.english);

}

public class E {

public static void main(String args[]) {

List<Student> list=new LinkedList<Student>();

int score []={65,76,45,99,77,88,100,79};

String name[]={"张三","李四","旺季","加戈","为哈","周和","赵李","将集"};

for(int i=0;i<score.length;i++){

list.add(new Student(score[i],name[i]));

}

Iterator<Student> iter=list.iterator();

TreeSet<Student> mytree=new TreeSet<Student>();

while(iter.hasNext()){

Student stu=iter.next();

mytree.add(stu);

}

Iterator<Student> te=mytree.iterator();

while(te.hasNext()) {

Student stu=te.next();

System.out.println(""+stu.name+" "+stu.english);

}

3. import java.util.*;

class UDiscKey implements Comparable {

double key=0;

UDiscKey(double d) {

key=d;

}

public int compareTo(Object b) {

UDiscKey disc=(UDiscKey)b;

if((this.key-disc.key)==0)

return -1;

else

return (int)((this.key-disc.key)*1000);

}

class UDisc{

int amount;

double price;

UDisc(int m,double e) {

amount=m;

price=e;

}

public class E {

public static void main(String args[ ]) {

TreeMap<UDiscKey,UDisc> treemap= new TreeMap<UDiscKey,UDisc>();

int amount[]={1,2,4,8,16};

double price[]={867,266,390,556};

UDisc UDisc[]=new UDisc[4];

for(int k=0;k<UDisc.length;k++) {

UDisc[k]=new UDisc(amount[k],price[k]);

}

UDiscKey key[]=new UDiscKey[4] ;

for(int k=0;k<key.length;k++) {

key[k]=new UDiscKey(UDisc[k].amount);

}

for(int k=0;k<UDisc.length;k++) {

treemap.put(key[k],UDisc[k]);

}

int number=treemap.size();

Collection<UDisc> collection=treemap.values();

Iterator<UDisc> iter=collection.iterator();

while(iter.hasNext()) {

UDisc disc=iter.next();

System.out.println(""+disc.amount+"G "+disc.price+"元");

}

treemap.clear();

for(int k=0;k<key.length;k++) {

key[k]=new UDiscKey(UDisc[k].price);

}

for(int k=0;k<UDisc.length;k++) {

treemap.put(key[k],UDisc[k]);

}

number=treemap.size();

collection=treemap.values();

iter=collection.iterator();

while(iter.hasNext()) {

UDisc disc=iter.next();

System.out.println(""+disc.amount+"G "+disc.price+"元");

}

习题十六（第16章）

1． import java.applet.*;

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class Xiti2 extends Applet implements ActionListener

{ TextField text1,text2;

Label label;

public void init()

{ text1=new TextField(10);

text2=new TextField(20);

Box box1=Box.createHorizontalBox();

Box box2=Box.createHorizontalBox();

Box boxV=Box.createVerticalBox();

box1.add(new Label("输入一个数回车确定:"));

box1.add(text1);

label=new Label("数的平方:");

box2.add(label);

box2.add(text2);

boxV.add(box1);

boxV.add(box2);

add(boxV);

text2.setEditable(false);

text1.addActionListener(this);

}

public void actionPerformed(ActionEvent e)

{ String number=e.getActionCommand();

try{ double n=Double.parseDouble(number);

double m=n*n;

label.setText(n+"的平方:");

text2.setText(""+m);

text1.setText("");

validate();

}

catch(NumberFormatException exp)

{ text2.setText(""+exp);

}

2． import java.applet.*;

import java.awt.*;

public class Rect extends Applet {

int w,h;

public void init() {

String s1=getParameter("width"); //从html得到"width"的值。

String s2=getParameter("height"); //从html得到"height"的值。

w=Integer.parseInt(s1);

h=Integer.parseInt(s2);

}

public void paint(Graphics g) {

g.drawRect(10,10,w,h);

}

/*<applet code= Rect.class width=280 height=500>

</applet>*/