JAVA语言程序设计（基础篇）第九章答案

JAVA语言程序设计（基础篇）第九章答案

习题9.1

public class SimpleRectangle {
double width;
double height;
SimpleRectangle(){
width = 1;
height = 1;
}
SimpleRectangle(double newWidth, double newHeight){
width = newWidth;
height = newHeight;
}

public double getArea(){
double area = width * height;
return area;
}

public double getPerimeter(){
double perimeter = (width + height) * 2;
return perimeter;
}
}

public class TestSimpleRectangle {
public static void main(String[] args){
SimpleRectangle rectangle1 = new SimpleRectangle(4,40);
SimpleRectangle rectangle2 = new SimpleRectangle(3.5,35.9);
System.out.println("rectangle 1 width is " + rectangle1.width +
" rectangle 1 height is " + rectangle1.height +
" area is " + rectangle1.getArea() +
" permiter is " + rectangle1.getPerimeter());

System.out.println("rectangle 2 width is " + rectangle2.width +
" rectangle 1 height is " + rectangle2.height +
" area is " + rectangle2.getArea() +
" permiter is " + rectangle2.getPerimeter());
}
}

习题9.2

public class Stock {
String symbol;
String name;
double previousClosingPrice;
double currentPrice;
Stock(String newSymbol, String newName){
symbol = newSymbol;
name = newName;
}
public double getChangePercent(){
double changePercent = (currentPrice - previousClosingPrice) / previousClosingPrice;
return changePercent;
}
public void setCurrentPrice(double newCurrentPrice){
currentPrice = newCurrentPrice;
}
public void setPreviousClosingPrice(double newPreviousClosingPrice){
previousClosingPrice = newPreviousClosingPrice;
}
}

public class TestStock {
public static void main(String[] args){
Stock stock1 = new Stock("ORCL", "Oracle Corporation");
stock1.setPreviousClosingPrice(34.5);
stock1.setCurrentPrice(34.35);
//System.out.println("The change percent is " + stock1.getChangePercent() * 100 +"%");
System.out.printf("The change percent is %5.2f%%\n", stock1.getChangePercent() * 100);
}
}

习题9.3

import java.util.Date;

public class TestUsingDateLib {
public static void main(String[] args){
Date date = new Date();
for(int i = 0; i < 8; i++){
long time = 10000 * (long)(Math.pow(10, i));
date.setTime(time);
System.out.println(date.toString());
}
}
}

习题9.4

import java.util.Random;;
public class TestRandomLib {
public static void main(String[] args){
Random random1 = new Random(1000);
System.out.println("From random 1:");
for(int i = 0; i < 50; i++){
System.out.print(random1.nextInt(100) + " ");
}

Random random2 = new Random(1000);
System.out.println("\nFrom random 2:");
for(int i = 0; i < 50; i++){
System.out.print(random2.nextInt(100) + " ");
}

}
}

习题9.5

import java.util.GregorianCalendar;
public class TestUsingGregorianCalendar {
public static void main(String[] args){
GregorianCalendar gregorianCalendar = new GregorianCalendar();
gregorianCalendar.get(GregorianCalendar.YEAR);
System.out.println(gregorianCalendar.get(GregorianCalendar.YEAR) + " " +
(gregorianCalendar.get(GregorianCalendar.MONTH) + 1) + " " +
gregorianCalendar.get(GregorianCalendar.DAY_OF_MONTH));
gregorianCalendar.setTimeInMillis(1234567898765L);
//System.out.print();

}
}

习题9.6

public class StopWatch {
private long startTime;
private long endTime;
StopWatch(){
startTime = System.currentTimeMillis();
}
public void start(){
startTime = System.currentTimeMillis();
}
public void stop(){
endTime = System.currentTimeMillis();
}
public long getElapsedTime(){
return endTime - startTime;
}
}

public class TestStopWatch {
public static void main(String[] args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
Hanoi hanoi = new Hanoi();
hanoi.hanoi(20, 'A', 'B', 'C');
stopWatch.stop();
System.out.println(stopWatch.getElapsedTime());
}
}

class Hanoi {
/**
*
* @param n 盘子的数目
* @param origin 源座
* @param assist 辅助座
* @param destination 目的座
*/
public void hanoi(int n, char origin, char assist, char destination) {
if (n == 1) {
move(origin, destination);
} else {
hanoi(n - 1, origin, destination, assist);
move(origin, destination);
hanoi(n - 1, assist, origin, destination);
}
}
// Print the route of the movement
private void move(char origin, char destination) {
System.out.println("Direction:" + origin + "--->" + destination);
}
}

习题9.7

import java.util.Date;
public class Account {
private int id;
private double balance;
private double annualInterestRate;
private Date dateCreated;
Account(){
id = 0;
balance = 0;
annualInterestRate = 0;
//dateCreated.getDate();
//dateCreated.toGMTString();
}
/**
* @param uId 用户ID
* @param initBalance 初始余额
* */
Account(int uId, double initBalance){
id = uId;
balance = initBalance;
}
public void setId(int newId){
id = newId;
}
public int getId(){
return id;
}

public void setBalance(int newBalance){
balance = newBalance;
}
public double getBalance(){
return balance;
}
public void setInterestAnnualRate(double newAnnualRate){
annualInterestRate = newAnnualRate;
}
public double getInterestAnnualRate(){
return annualInterestRate;
}
public Date getDateCreated(){
return dateCreated;
}
public double getMonthlyInterestRate(){
return balance * annualInterestRate / 100 / 12;
}
public void withDraw(double withDrawBalance){
balance -= withDrawBalance;
}
public void deposit(double depositBalance){
balance += depositBalance;
}
}

public class TestAccount {
public static void main(String[] args){
Account account1 = new Account(1122, 20000);
account1.setInterestAnnualRate(4.5);
account1.withDraw(2500);
account1.deposit(3000);
System.out.println(account1.getBalance() + "\n" +
account1.getMonthlyInterestRate() + "\n" +
account1.getDateCreated());
}
}

习题9.8

public class Fan {
private final short SLOW = 1;
private final short MEDIUM = 2;
private final short FAST = 3;
private int speed;
private boolean on;
private double radius;
private String color;
Fan(){
speed = SLOW;
on = false;
radius = 5;
color = "blue";
}

public void turnOn(){
on = true;
}
public void turnOff(){
on =false;
}
public void setRadius(double newRadius){
radius = newRadius;
}
public double getRadius(){
return radius;
}
public void setColor(String newColor){
color = newColor;
}
public String getColor(){
return color;
}
public void setSpeed(int newSpeed){
speed = newSpeed;
}
public int getSpeed(){
return speed;
}
public void ToString(){
if(on)
System.out.println(speed + " " + color + " " + radius);
else
System.out.println("fan is off");
}

}

public class TestFan {
public static void main(String[] args){
Fan fan1 = new Fan();
fan1.setSpeed(3);
fan1.setRadius(10);
fan1.setColor("yellow");
fan1.turnOn();
fan1.ToString();

Fan fan2 = new Fan();
fan2.setSpeed(2);
fan2.setColor("blue");
fan2.turnOff();
fan2.ToString();
}
}

习题9.9

public class RegularPolygon {
private int n;
private double side;
private double x;
private double y;
RegularPolygon(){
n = 3;
side = 1.0;
x = 0;
y = 0;
}
/**
* @param newN    边的个数
* @param newSide 边长
* */
RegularPolygon(int newN, double newSide){
n = newN;
side = newSide;
x = 0;
y = 0;
}
/**
* @param newN        边的个数
* @param newSide     边长
* @param newCenterX  中心坐标X
* @param newCenterY  中心坐标Y
* */
RegularPolygon(int newN, double newSide, double newCenterX, double newCenterY){
n = newN;
side = newSide;
x = newCenterX;
y = newCenterY;
}

public void setN(int newN){
n = newN;
}
public int getN(){
return n;
}

public void setSide(double newSide){
side = newSide;
}
public double getSide(){
return side;
}
public void setCenerX(double newX){
x = newX;
}
public double getCenerX(){
return x;
}
public void setCenerY(double newY){
y = newY;
}
public double getCenerY(){
return y;
}
public double getPerimeter(){
return n*side;
}
public double getArea(){
double area;
area = (n * Math.pow(side, 2)) / (4 * Math.tan((Math.PI / n)));
return area;
}
}

public class TestRegularPolygon {

public static void main(String[] args){
RegularPolygon regularPolygon1 = new RegularPolygon();
RegularPolygon regularPolygon2 = new RegularPolygon(6,4);
RegularPolygon regularPolygon3 = new RegularPolygon(10,4,5.6,7.8);
System.out.println("regularPolygon1 premiter is " + regularPolygon1.getPerimeter()
+ " area is " + regularPolygon1.getArea());
System.out.println("regularPolygon2 premiter is " + regularPolygon2.getPerimeter()
+ " area is " + regularPolygon2.getArea());
System.out.println("regularPolygon3 premiter is " + regularPolygon3.getPerimeter()
+ " area is " + regularPolygon3.getArea());
}
}

习题9.10

public class QuadraticEquation {
private double a,b,c;
QuadraticEquation(double newA, double newB, double newC){
a = newA;
b = newB;
c = newC;
}
public double getA(){
return a;
}
public double getB(){
return b;
}
public double getC(){
return c;
}
public double getDiscriminant(){
return Math.pow(b, 2) - 4 * a * c;
}
public double getRoot1(){
if(this.getDiscriminant() >= 0)
return (-b + Math.pow(this.getDiscriminant(), 0.5)) / (2 * a);
else
return 0;
}
public double getRoot2(){
if(this.getDiscriminant() >= 0)
return (-b - Math.pow(this.getDiscriminant(), 0.5)) / (2 * a);
else
return 0;
}
}

import java.util.Scanner;
public class TestQuadraticEquation {
public static void main(String[] args){

final double EPSILON = 1E-14;

Scanner input = new Scanner(System.in);
System.out.println("Enter the equation's a");
double a = input.nextDouble();
System.out.println("Enter the equation's b");
double b = input.nextDouble();
System.out.println("Enter the equation's c");
double c = input.nextDouble();
input.close();
QuadraticEquation equation = new QuadraticEquation(a,b,c);

if(equation.getDiscriminant() > EPSILON){
System.out.println("root1 is " + equation.getRoot1() + " root2 is " + equation.getRoot2());
}
else if(Math.abs(equation.getDiscriminant() - 0) <= EPSILON)
System.out.println("root is " + equation.getRoot1());
else
System.out.println("Ths equation has no roots.");

}
}

习题9.11

public class LinearEquation {
final double EPSILON = 1E-14;
private double a,b,c,d,e,f;
LinearEquation(double newA, double newB, double newC,
double newD, double newE, double newF){
a = newA;
b = newB;
c = newC;
d = newD;
e = newE;
f = newF;
}
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 isSolveable(){
return Math.abs((a *d - b * c) - 0) >= EPSILON ? true : false;
}
public double getX(){
return (e * d - b * f) / (a *d - b * c);
}
public double getY(){
return (a * f - e * c) / (a *d - b * c);
}

}

import java.util.Scanner;
public class TestLinearEquation {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.println("Enter a:");
double a = input.nextDouble();
System.out.println("Enter b:");
double b = input.nextDouble();
System.out.println("Enter c:");
double c = input.nextDouble();
System.out.println("Enter d:");
double d = input.nextDouble();
System.out.println("Enter e:");
double e = input.nextDouble();
System.out.println("Enter f:");
double f = input.nextDouble();
input.close();
LinearEquation linearEquation = new LinearEquation(a,b,c,d,e,f);
if(linearEquation.isSolveable())
System.out.println("x is " + linearEquation.getX() + " y is " + linearEquation.getY());
else
System.out.println("The equation has no solution.");

}
}

习题9.12

import java.util.Scanner;
public class CrossPoint {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.println("Enter x1:");
double x1 = input.nextDouble();
System.out.println("Enter y1:");
double y1 = input.nextDouble();
System.out.println("Enter x2:");
double x2 = input.nextDouble();
System.out.println("Enter y2:");
double y2 = input.nextDouble();
System.out.println("Enter x3:");
double x3 = input.nextDouble();
System.out.println("Enter y3:");
double y3 = input.nextDouble();
System.out.println("Enter x4:");
double x4 = input.nextDouble();
System.out.println("Enter y4:");
double y4 = input.nextDouble();
input.close();
LinearEquation linearEquation = new LinearEquation(y1 - y2, -(x1 - x2), y3 - y4, -(x3 - x4),
(y1 - y2) * x1 - (x1 - x2) * y1,
(y3 - y4) * x3 - (x3 - x4) * y3);
if(linearEquation.isSolveable())
System.out.println("cross point x is " + linearEquation.getX() +
"cross point y is " + linearEquation.getY());
else
System.out.println("Have no cross point.");
}
}

习题9.13

public class Location {
public int row, column;
public double maxValue;
}

import java.util.Scanner;
public class TestLocation {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.println("Enter the number of rows in the array:");
int row = input.nextInt();
System.out.println("Enter the number of columns in the array:");
int column = input.nextInt();

double[][] array = new double[row][column];

for(int i = 0; i < array.length; i++){
for(int j = 0; j < array[1].length; j++){
System.out.println("Enter the value of array(" + i + ", " + j);
array[i][j] = input.nextDouble();
}
}
input.close();
Location resultLocation = locateLargest(array);
System.out.println("The location of the largest element is " + resultLocation.maxValue +
" at (" + resultLocation.row + ", " + resultLocation.column + ")");

}

public static Location locateLargest(double[][] a){
Location location = new Location();
location.maxValue = a[0][0];
location.row = 0;
location.column = 0;
for(int row = 0; row < a.length; row++){
for(int column = 0; column < a[1].length; column++){
if(location.maxValue < a[row][column])
{
location.maxValue = a[row][column];
location.row = row;
location.column = column;
}
}
}
return location;
}

}