JAVA语言程序设计（基础篇） 第十版——第九章 对象和类 （参考答案）
提示：第9~13章的练习题要达到下面三个目标：
1.设计类并画出UML类图；
2.实现UML中的类；
3.实用类开发应用程序.
个人建议：去下载个软件画UML类图，如，
里面可直接将你画的UML类图转换为代码，省时便捷，具体转换操作去百度百度。
（9.2~9.5节）
9.1（矩形类Rectangle）
package p9;
public class Rectangle {
public double width;
public double height;
public Rectangle() {
width=1;
height=1;
}
public Rectangle(double newWidth, double newHeight) {
width=newWidth;
height=newHeight;
}
public double getArea() {
return width*height;
}
public double getPerimeter() {
return 2*(width+height);
}
}
package p9;
public class Test1 {
public static void main(String[] args) {
//创建对象 1
Rectangle object1=new Rectangle(4, 40);
//创建对象 2
Rectangle object2=new Rectangle(3.5, 35.9);
System.out.print("第一个矩形： ");
System.out.print(" 宽："+object1.width+" 高："+object1.height);
System.out.println(" 面积："+object1.getArea()+" 周长："+object1.getPerimeter());
System.out.print("第二个矩形： ");
System.out.print(" 宽："+object2.width+" 高："+object2.height);
System.out.println(" 面积："+object2.getArea()+" 周长："+object2.getPerimeter());
}
}
9.2(股票类 Stock)
package p9;
public class Stock {
public String symbol;
public String name;
public double previousClosingPrice;
public double currentPrice;
public Stock(String newSymbol, String newName) {
symbol=newSymbol;
name=newName;
}
public double getChangePercent() {
return (currentPrice-previousClosingPrice)/100 ;
}
public void setPreviousClosingPrice(double newPreviousClosingPrice) {
previousClosingPrice=newPreviousClosingPrice;
}
public void setCurrentPrice(double CurrentPrice) {
currentPrice=CurrentPrice;
}
}
package p9;
public class Test2 {
public static void main(String[] args) {
//创建一个对象
Stock object=new Stock("ORCL","Oracle Corporation");
object.setPreviousClosingPrice(34.5);
object.setCurrentPrice(35.5);
System.out.println("市值变化的百分比是："+object.getChangePercent());
}
}
(9.6节)
*9.3（使用日期类Date）
package p9;
public class Test3 {
public static void main(String[] args) {
//创建一个Date类
java.util.Date date=new java.util.Date();
date.setTime(10000);
System.out.println(date.toString());
date.setTime(100000);
System.out.println(date.toString());
date.setTime(1000000);
System.out.println(date.toString());
date.setTime(10000000);
System.out.println(date.toString());
date.setTime(100000000);
System.out.println(date.toString());
date.setTime(1000000000);
System.out.println(date.toString());
//注意：长整数要在后面加上“L”，不然不能被识别
date.setTime(10000000000L);
System.out.println(date.toString());
//注意：长整数要在后面加上“L”，不然不能被识别
date.setTime(100000000000L);
System.out.println(date.toString());
}
}
*9.4（使用随机类Random）
package p9;
import java.util.Random;
public class Test4 {
public static void main(String[] args) {
Random random=new Random(1000);
for(int i=1; i<=50; i++) {
if(i%10==0)
System.out.println(random.nextInt(100));
else
System.out.print(random.nextInt(100)+" ");
}
}
}
*9.5（使用公历类GregorianCalendar）
在构造方法里我直接输入了 我的当前日期
因为我发现，用它的无参构造方法时，显示的月份少一个月，我也不知道为什么。
package p9;
import java.util.GregorianCalendar;
public class Test5 {
public static void main(String[] args) {
//在构造方法里我直接输入了 我的当前日期
GregorianCalendar object=new GregorianCalendar(2020,4,8);
System.out.println(object.get(GregorianCalendar.YEAR)+"年"
+ object.get(GregorianCalendar.MONTH)+"月"
+ object.get(GregorianCalendar.DATE)+"日");
object.setTimeInMillis(1234567898765L);
System.out.println(object.get(GregorianCalendar.YEAR)+"年"
+ object.get(GregorianCalendar.MONTH)+"月"
+ object.get(GregorianCalendar.DATE)+"日");
}
}
（9.7~9.9节）
*9.6（秒表）
package p9;
public class StopWatch {
private long startTime;
private long endTime;
public StopWatch() {
java.util.Date date=new java.util.Date();
startTime=date.getTime();
}
public void start(long startTime) {
this.startTime=startTime;
}
public void Stop(long endTime) {
this.endTime=endTime;
}
public long getElapsedTime() {
java.util.Date time=new java.util.Date();
return time.getTime();
}
public long getStartTime() {
return startTime;
}
public long getEndTime() {
return endTime;
}
}
package p9;
public class Test6 {
public static void main(String[] args) {
StopWatch object=new StopWatch();
int[] n=new int[100000];
for(int i=0; i<100000; i++) {
n[i]=(int) (Math.random()*100);
}
selectionSort(n);
object.Stop(object.getElapsedTime());
long executeTime=object.getEndTime()-object.getStartTime();
System.out.println("执行时间为： "+executeTime+" Milliseconds.");
}
public static void selectionSort(int[] list) {
for(int i=0;i
9.7（账户类Account）
package p9;
import java.util.Date;
public class Account {
public int id=0;//用户名
public double balance=0;//余额
public double annualInteresRate=0;//当前利率
public java.util.Date dateCreated;//存储开户日期
//无参构造方法
public Account(){
Date dateCreated=new Date();
this.dateCreated=dateCreated;
}
//有参构造方法
public Account(int id, double balance){
Date dateCreated=new Date();
this.dateCreated=dateCreated;
this.id=id;
this.balance=balance;
}
public int getId(){
return id;
}
public double getBalance() {
return balance;
}
public double getAnualInterestRate() {
return annualInteresRate;
}
public void setId(int id){
this.id=id;
}
public void setBalance(double balance) {
this.balance=balance;
}
//设置 年利率
public void setAnnualInterestRate(double annualInterestRate) {
this.annualInteresRate=annualInterestRate;
}
//获得开户日期
public String getDateCreated(){
return dateCreated.toString();
}
//月利息
public double getMonthlyInterestRate() {
return annualInteresRate/12;
}
//取钱
public double withDraw(double withdraw) {
return this.balance=this.balance-withdraw;
}
//存钱
public double deposit(double deposit) {
return this.balance=this.balance+deposit;
}
}
package p9;
import java.util.Date;
public class Test7 {
public static void main(String[] args) {
Account object=new Account( 1122, 20000 );
object.setAnnualInterestRate(4.5/100);
object.withDraw(2500);
object.deposit(3000);
System.out.println("余额："+object.getBalance()+"美元");
System.out.println("月利息："+object.getMonthlyInterestRate()*100+"%");
System.out.print("开户时间："+object.getDateCreated());
}
}
9.8(风扇类 Fan）
package p9;
public class Fan {
//常量，表示风扇的速度
public final int SLOW=1;
public final int MEDIUM=2;
public final int FAST=3;
//数据域
private int speed=SLOW;
private boolean on=false;
private double radius=5;
public String color="blue";
public int getSpeed(int speed) {
return speed;
}
public boolean getOn() {
return false;
}
public double getRadius() {
return radius;
}
public String getColor() {
return color;
}
public void setSpeed(int speed) {
this.speed=speed;
}
public void setOn(boolean on) {
this.on=on;
}
public void setRadius(double radius) {
this.radius=radius;
}
public void setColor(String color) {
this.color=color;
}
Fan(){
}
public String toString(){
if(on==true) {
return "速度："+this.speed+" 颜色："+this.color+" 半径："+this.radius;
}
else {
return "fan is off."+" 颜色："+this.color+" 半径："+this.radius;
}
}
}
package p9;
public class Test8 {
private static final int SLOW = 1;
private static final int MEDIUM = 2;
private static final int FAST = 3;
public static void main(String[] args) {
Fan object1=new Fan();
Fan object2=new Fan();
object1.setSpeed(FAST);
object1.setRadius(10);
object1.setColor("yellow");
object1.setOn(true);
object2.setSpeed(MEDIUM);
object2.setRadius(5);
object2.setColor("blue");
object2.setOn(false);
System.out.println("对象1： "+object1.toString());
System.out.println("对象2："+object2.toString());
}
}
**9.9（几何：正 n 边形）
package p9;
/** */
public class RegularPolygon
{
//多边形边数
private int n=3;
//多边形长度
private double side=1;
//多边形的X坐标
private double x=0;
//多边形的y坐标
private double y=0;
//无参构造方法
RegularPolygon()
{
}
//指定边数、长度、中心在（0，0）的正多边形的构造方法
RegularPolygon(int n, double side)
{
this.n=n;
this.side=side;
}
//指定边数、长度、中心在（x，y）的正多边形的构造方法
RegularPolygon(int n, double side, double x, double y)
{
this.n=n;
this.side=side;
this.x=x;
this.y=y;
}
/** */
public int getN()
{
return n;
}
/** */
public void setN(int n)
{
this.n=n;
}
/** */
public double getSide()
{
return side;
}
/** */
public void setSide(double side)
{
this.side=side;
}
/** */
public double getX()
{
return x;
}
/** */
public void setX(double x)
{
this.x=x;
}
/** */
public double getY()
{
return y;
}
/** */
public void setY(double y)
{
this.y=y;
}
//求周长
public double getPerimeter()
{
return n*side;
}
//求面积
public double getArea()
{
return (n*Math.pow(side, 2)) / ( 4 * Math.toDegrees( Math.tan(Math.PI/n ) ) );
}
}
package p9;
public class Test9 {
public static void main(String[] args) {
RegularPolygon object1=new RegularPolygon();
RegularPolygon object2=new RegularPolygon(6,4);
RegularPolygon object3=new RegularPolygon(10,4,5.6,7.8);
System.out.println("对象1： 周长："+object1.getPerimeter()+" 面积："+object1.getArea());
System.out.println("对象2： 周长："+object2.getPerimeter()+" 面积："+object2.getArea());
System.out.println("对象3： 周长："+object3.getPerimeter()+" 面积："+object3.getArea());
}
}
*9.10（代数：二次方程）
package p9;
public class QuadraticEquation {
private double a;
private double b;
private double c;
QuadraticEquation(double a, double b, double c) {
this.a=a;
this.b=b;
this.c=c;
}
public double getA() {
return a;
}
public double getB() {
return b;
}
public double getC() {
return c;
}
public double getDiscriminant() {
double p=Math.pow(b, 2)-4*a*c;
return p;
}
public double getRoot1() {
double r1=(-b+Math.sqrt(Math.pow(b, 2)-4*a*c)) / (2*a);
return r1;
}
public double getRoot2() {
double r2=(-b-Math.sqrt(Math.pow(b, 2)-4*a*c)) / (2*a);
return r2;
}
}
package p9;
import java.util.Scanner;
public class Test10 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("请输入a、b和c的值：");
double a=input.nextDouble();
double b=input.nextDouble();
double c=input.nextDouble();
input.close();
QuadraticEquation object=new QuadraticEquation(a,b,c);
System.out.println("a的值："+object.getA());
System.out.println("b的值："+object.getB());
System.out.println("c的值："+object.getC());
if(object.getDiscriminant()>0)
System.out.println("判别式>0,方程有两个根,分别为 r1:"+object.getRoot1()+" r2:"+object.getRoot2());
else if(object.getDiscriminant()==0)
System.out.println("判别式=0,方程只有一个根 r:"+object.getRoot1());
else
System.out.println("The equation has no roots.");
}
}
*9.11(代数：2x2 的线性方程)
package p9;
public class LinearEquation {
private double a;
private double b;
private double c;
private double d;
private double e;
private double f;
LinearEquation(double a, double b, double c, double d, double e, double f) {
this.a=a;
this.b=b;
this.c=c;
this.d=d;
this.e=e;
this.f=f;
}
public double getA() {
return a;
}
public double getB() {
return b;
}
public double getC() {
return c;
}
public double getD() {
return d;
}
public double getE() {
return e;
}
public double getF() {
return f;
}
public boolean isSolvable() {
if((this.a*this.d-this.b*this.c) != 0)
return true;
else
return false;
}
public double getX() {
double x=(this.e*this.d-this.b*this.f)/(this.a*this.d-this.b*this.c);
return x;
}
public double getY() {
double y=(this.a*this.f-this.e*this.c)/(this.a*this.d-this.b*this.c);
return y;
}
}
package p9;
import java.util.Scanner;
public class Test11 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("请输入a、b、c、d、e、f的值：");
double a=input.nextDouble();
double b=input.nextDouble();
double c=input.nextDouble();
double d=input.nextDouble();
double e=input.nextDouble();
double f=input.nextDouble();
LinearEquation object=new LinearEquation(a,b,c,d,e,f);
if(object.isSolvable())
System.out.println("X:"+object.getX()+" y:"+object.getY());
else
System.out.println("The equation has no solution.");
}
}
**9.12(几何：交点)
在上一题的基础上，我增加了两个数据域 g 和 h，两个方法：getG( )方法 和 getH( )方法，用来获得4个点的坐标
两点确定一条直线，点1（x1,y1）和点2(x2,y2)确定直线L1;
点3（x3,y3）和点4(x4,y4)确定直线L2;
利用（3.3题）的公式：
ax+by=e cx+dy=f
解得
x=(ed-bf)/(ad-bc) y=(af-ec)/(ad-bc)
其交点就是：（x，y）
若（ad-bc）=0,则说明这两条直线平行。
理解了以上公式，再带入（3.25题）的公式，即可求解。
在（3.25题）中，公式可这样理解：
a=（y1-y2）
b= -（x1-x2）
c=（y3-y4）
d= -（x3-x4）
e=（y1-y2）x1-（x1-x2）y1
f=（y3-y4）x3-（x3-x4）y3
package p9;
public class LinearEquation {
private double x1;
private double y1;
private double x2;
private double y2;
private double x3;
private double y3;
private double x4;
private double y4;
LinearEquation(double x1, double y1, double x2, double y2, double x3, double y3, double x4, double y4) {
this.x1=x1;
this.y1=y1;
this.x2=x2;
this.y2=y2;
this.x3=x3;
this.y3=y3;
this.x4=x4;
this.y4=y4;
}
public double getX1() {
return x1;
}
public double getY1() {
return y1;
}
public double getX2() {
return x2;
}
public double getY2() {
return y2;
}
public double getX3() {
return x3;
}
public double getY3() {
return y3;
}
public double getX4() {
return x4;
}
public double getY4() {
return y4;
}
public boolean isSolvable() {
if(((y1-y2)*-(x3-x4))-(-(x1-x2)*(y3-y4)) != 0)
return true;
else
return false;
}
public double getX() {
double x=(((y1-y2)*x1-(x1-x2)*y1)*( -(x3-x4))-( -(x1-x2))*((y3-y4)*x3-(x3-x4)*y3))
/ (((y1-y2)*-(x3-x4))-(-(x1-x2)*(y3-y4))) ;
return x;
}
public double getY() {
double y=(((y1-y2))*((y3-y4)*x3-(x3-x4)*y3)-((y1-y2)*x1-(x1-x2)*y1)*((y3-y4)))
/ (((y1-y2)*-(x3-x4))-(-(x1-x2)*(y3-y4))) ;
return y;
}
}
package p9;
import java.util.Scanner;
public class Test12 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("请输入坐标：x1,y1,x2,y2,x3,y3,x4,y4的值：");
double x1=input.nextDouble();
double y1=input.nextDouble();
double x2=input.nextDouble();
double y2=input.nextDouble();
double x3=input.nextDouble();
double y3=input.nextDouble();
double x4=input.nextDouble();
double y4=input.nextDouble();
input.close();
//创建对象
LinearEquation object=new LinearEquation(x1,y1,x2,y2,x3,y3,x4,y4);
if(object.isSolvable())
System.out.print("The intersecting point is at (" + object.getX() + ", " + object.getY() + ")");
else
System.out.print(" The two lines are parallel ");
}
}
**9.13（位置类 Location）
package p9;
public class Location {
public int row;
public int column;
public double maxValue;
public static String locateLargest(double[][] a) {
double maxValue=a[0][0];
int row=0;
int column=0;
for(int i=0; imaxValue) {
maxValue=a[i][j];
row=i;
column=j;
}
}
}
return "The location of the largest element is "
+maxValue+" at ("+row+", "+column+")";
}
}
package p9;
import java.util.Scanner;
public class Test13 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("Enter the number of rows and columns in the array:");
int rows=input.nextInt();
int columns=input.nextInt();
double[][] n=new double[rows][columns];
System.out.println("Enter the array");
for(int row=0; row