4.2节 + （4.3~4.6节）

4.2节

4.1（几何：五边形的面积）

import java.util.Scanner;public class C1 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter the length from the center to a vertex: ");double r=input.nextFloat();input.close();double s=2*r*Math.sin(Math.PI/5);double area=(5*s*s)/(4*Math.tan(Math.PI/5));System.out.printf("The area of the pentagon is %5.2f ", area);}}

*4.2（几何：最大圆距离）

这题难就难在如何将从控制台接收的一个字符串将它分割，就是将字符串里的( ， )逗号字符和（）空格字符删掉。

也就是如何从一个字符串里获取子串的问题，我还特地去百度了一下（，）逗号的 Unicode值为：' \u002C ' .

然后将分割得到的数值型字符串转化为数值，就没什么难点了(#^.^#)

import java.util.Scanner;public class C2 {public static void main(String[] args) {Scanner input=new Scanner(System.in);//用字符串接收s1、s2System.out.print("Enter point 1 (latitude and longitude) in degrees: ");String s1=input.nextLine();System.out.print("Enter point 2 (latitude and longitude) in degrees: ");String s2=input.nextLine();//input.close();String s11="";String s12="";//以','字符逗号为分割点，将s1字符串分为两部分if(s1.length()!=0 && !s1.equals("")) {for(int i=0;i<s1.length();i++) {if(s1.charAt(i) == '\u002C') {s11=s1.substring(0,i);s12=s1.substring(i+1);}}}//用trim()方法删去字符串两边的空白字符String s5=s11.trim();String s6=s12.trim();//将数值型的字符串 转换为 数值double degree1=Double.parseDouble(s5);double degree2=Double.parseDouble(s6);String s21="";String s22="";//以','字符逗号为分割点，将s2字符串分为两部分if(s2.length()!=0 && !s2.equals("")) {for(int i=0;i<s2.length();i++) {if(s2.charAt(i) == '\u002C') {s21=s2.substring(0,i);s22=s2.substring(i+1);}}}//用trim()方法删去字符串两边的空白字符String s7=s21.trim();String s8=s22.trim();//将数值型的字符串 转换为 数值double degree3=Double.parseDouble(s7);double degree4=Double.parseDouble(s8);/*上面代码是完成input.nextLine()方法在控制台的接收，并将 数值型字符串 转换为  数值，进行下面的计算		*///下面的代码是完成公式套用计算double x1=Math.toRadians(degree1);double y1=Math.toRadians(degree2);double x2=Math.toRadians(degree3);double y2=Math.toRadians(degree4);double d= 6371.01 * Math.acos(Math.sin(x1)*Math.sin(x2) + Math.cos(x1)*Math.cos(x2)*Math.cos(y1-y2))  ;System.out.println("The distance between the two points is " + d +" km ");}}

*4.3（几何：估算面积）

首先找出个地方的经纬度：

地名：Savannah     纬度：31.9714   经度：-81.0716

地名：Charlotte      纬度：35.2731    经度：-80.9571

然后给地名先标个点，以致等会儿计算时不会混淆

第某个点：某地名（纬度，经度）

第一个点：Atlanta(33.46, 84.25)

第二个点：Orlando(28.3, 81.22)

第三个点：Savannah(31.9714, -81.0716 )

第四个点：Charlotte(35.2731, -80.9571)

其实没啥难度，也就是找公式、找经纬度麻烦些。

import java.util.Scanner;public class C3 {public static void main(String[] args) {Scanner input=new Scanner(System.in);//用字符串接收s1、s2、s3、s4System.out.print("Enter point 1 (latitude and longitude) in degrees: ");String s1=input.nextLine();System.out.print("Enter point 2 (latitude and longitude) in degrees: ");String s2=input.nextLine();System.out.print("Enter point 3 (latitude and longitude) in degrees: ");String s3=input.nextLine();System.out.print("Enter point 4 (latitude and longitude) in degrees: ");String s4=input.nextLine();input.close();//以下是 处理s1字符串···············································String s11="";String s12="";//以','字符逗号为分割点，将s1字符串分为两部分if(s1.length()!=0 && !s1.equals("")) {for(int i=0;i<s1.length();i++) {if(s1.charAt(i) == '\u002C') {s11=s1.substring(0,i);s12=s1.substring(i+1);}}}//用trim()方法删去字符串两边的空白字符String s5=s11.trim();String s6=s12.trim();//将数值型的字符串 转换为 数值double degree1=Double.parseDouble(s5);double degree2=Double.parseDouble(s6);//以下是 处理s2字符串···············································String s21="";String s22="";//以','字符逗号为分割点，将s2字符串分为两部分if(s2.length()!=0 && !s2.equals("")) {for(int i=0;i<s2.length();i++) {if(s2.charAt(i) == '\u002C') {s21=s2.substring(0,i);s22=s2.substring(i+1);}}}//用trim()方法删去字符串两边的空白字符String s7=s21.trim();String s8=s22.trim();//将数值型的字符串 转换为 数值double degree3=Double.parseDouble(s7);double degree4=Double.parseDouble(s8);		//以下是 处理s3字符串···············································String s31="";String s32="";//以','字符逗号为分割点，将s3字符串分为两部分if(s3.length()!=0 && !s3.equals("")) {for(int i=0;i<s3.length();i++) {if(s3.charAt(i) == '\u002C') {s31=s3.substring(0,i);s32=s3.substring(i+1);}}}//用trim()方法删去字符串两边的空白字符String s9=s31.trim();String s10=s32.trim();//将数值型的字符串 转换为 数值double degree5=Double.parseDouble(s9);double degree6=Double.parseDouble(s10);//以下是 处理s4字符串···············································String s41="";String s42="";//以','字符逗号为分割点，将s4字符串分为两部分if(s4.length()!=0 && !s4.equals("")) {for(int i=0;i<s4.length();i++) {if(s4.charAt(i) == '\u002C') {s41=s4.substring(0,i);s42=s4.substring(i+1);}}}//用trim()方法删去字符串两边的空白字符String s111=s41.trim();String s121=s42.trim();//将数值型的字符串 转换为 数值double degree7=Double.parseDouble(s111);double degree8=Double.parseDouble(s121);//下面是求两点间的距离···············································
//先求 点1和点2 之间的距离//度数转换成弧度double x1=Math.toRadians(degree1);double y1=Math.toRadians(degree2);double x2=Math.toRadians(degree3);double y2=Math.toRadians(degree4);double d12= 6371.01 * Math.acos(Math.sin(x1)*Math.sin(x2) + Math.cos(x1)*Math.cos(x2)*Math.cos(y1-y2))  ;//再求 点2和点3 之间的距离//度数转换成弧度double x3=Math.toRadians(degree5);double y3=Math.toRadians(degree6);double d23= 6371.01 * Math.acos(Math.sin(x2)*Math.sin(x3) + Math.cos(x2)*Math.cos(x3)*Math.cos(y2-y3))  ;//再求 点1和点3 之间的距离double d13= 6371.01 * Math.acos(Math.sin(x1)*Math.sin(x3) + Math.cos(x1)*Math.cos(x3)*Math.cos(y1-y3))  ;//再求 点3和点4 之间的距离//度数转换成弧度double x4=Math.toRadians(degree7);double y4=Math.toRadians(degree8);double d34= 6371.01 * Math.acos(Math.sin(x3)*Math.sin(x4) + Math.cos(x3)*Math.cos(x4)*Math.cos(y3-y4))  ;//再求 点1和点4 之间的距离double d14= 6371.01 * Math.acos(Math.sin(x1)*Math.sin(x4) + Math.cos(x1)*Math.cos(x4)*Math.cos(y1-y4))  ;//距离算完了，就可以利用算三角形面积公式 求出这个四边形的面积
/*三角形面积公式：s=(边1+边2+边3)/2   面积=根号下（   (s*(s-边1)*(s-边2)*(s-边3))  ）*///第一个三角形的面积		double ss1=(d12+d23+d13)/2;double area1=Math.sqrt((ss1*(ss1-d12)*(ss1-d23)*(ss1-d13)));//第二个三角形的面积double ss2=(d13+d34+d14)/2;double area2=Math.sqrt((ss2*(ss2-d13)*(ss2-d34)*(ss2-d14)));//四边形的面积double area= area1 + area2 ;System.out.println("The total Area is " + area);}}

运行结果：

4.4（几何：六边形面积）

import java.util.Scanner;public class C4 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter the side: ");double s=input.nextDouble();input.close();double area=(6*s*s)/(4*Math.tan(Math.PI/6));System.out.printf("The area of the hexagon is %5.2f", area);}}

*4.5（几何：正多边形的面积）

这个tan(-)里面放啥我也不知道，乱编的我

我用的公式和书上的不一样，我用自己瞎编的公式：面积=(n*s*s) / (4*tan(180°/n)

import java.util.Scanner;public class C5 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter the number of sides: ");int n=input.nextInt();System.out.print("Enter the side: ");double s=input.nextDouble();double area=(n*s*s)/(4*Math.tan(Math.toRadians(180)/n));System.out.println("The area of the polygon is " + area);}}

结果也和书上的一样的

*4.6（圆上的随机点）

import java.util.Scanner;public class C6 {public static void main(String[] args) {int r=40;//半径//第 1个随机点int a1=(int) (Math.random()*2*Math.PI);double x1=r*Math.cos(a1);double y1=r*Math.sin(a1);//第 2个随机点int a2=(int) (Math.random()*2*Math.PI);double x2=r*Math.cos(a2);double y2=r*Math.sin(a2);//第 3个随机点int a3=(int) (Math.random()*2*Math.PI);double x3=r*Math.cos(a3);double y3=r*Math.sin(a3);	double d12=Math.sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));double d23=Math.sqrt((x2-x3)*(x2-x3) + (y2-y3)*(y2-y3));double d13=Math.sqrt((x1-x3)*(x1-x3) + (y1-y3)*(y1-y3));double a=d23;double b=d13;double c=d12;//求角度double la=Math.toDegrees( Math.acos((a*a-b*b-c*c)/(-2*b*c)) );double lb=Math.toDegrees( Math.acos((b*b-a*a-c*c)/(-2*a*c)) );double lc=Math.toDegrees( Math.acos((c*c-a*a-b*b)/(-2*a*b)) );System.out.println(" ∠A的度数为 ：" + (int)la +"°");System.out.println(" ∠B的度数为 ：" + (int)lb +"°");System.out.println(" ∠C的度数为 ：" + (int)lc +"°");}}

*4.7（顶点坐标）

这一题请不用纠结，直接套用上一题4.6题的公式就好了

X= r *cos(a)  and   Y= r *sin(a)  公式使用说明在*4.6题的题目里。

import java.util.Scanner;public class C7 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter the radius of the bounding circle: ");double r=input.nextDouble();input.close();//以x轴为基准，得出度数double degree1=18;double degree2=90;double degree3=162;double degree4=-126;double degree5=-54;/*与上一题*4.6一样，运用它的 X ，Y 的转换公式，你 4.6题懂了，4.7题也就自然懂了，很简单的，就是套用公式，想都不用想的那种*/double x1=r*Math.cos(Math.toRadians(degree1));double y1=r*Math.sin(Math.toRadians(degree1));double x2=r*Math.cos(Math.toRadians(degree2));double y2=r*Math.sin(Math.toRadians(degree2));double x3=r*Math.cos(Math.toRadians(degree3));double y3=r*Math.sin(Math.toRadians(degree3));double x4=r*Math.cos(Math.toRadians(degree4));double y4=r*Math.sin(Math.toRadians(degree4));double x5=r*Math.cos(Math.toRadians(degree5));double y5=r*Math.sin(Math.toRadians(degree5));System.out.println("The coordinates of five points on the pentagon are ");  System.out.printf("( %7.4f , %7.4f) \n", x1, y1 );System.out.printf("( %7.4f , %7.4f) \n", x2, y2 );System.out.printf("( %7.4f , %7.4f) \n", x3, y3 );System.out.printf("( %7.4f , %7.4f) \n", x4, y4 );System.out.printf("( %7.4f , %7.4f) \n", x5, y5 );}}

4.3~4.6节

 *4.8（给出ASCII码对应的字符） 

我想哭了·············（我之前傻傻的想把十进制数化十六进制再化成字符，当然最后一步没实现，也不知道可不可以）

就这两行代码想死我了，最后恍然大悟的感觉就是，自己之前没有掌握这个知识点啦(￢︿̫̿￢☆)

知识点：

ASCII码的‘十进制数’转换为对应的‘字符’的方法：（字符+十进制数）！！！

import java.util.Scanner;public class C8 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter an ASCII code: integer:(0~127) :");int number=input.nextInt();char ch=(char) ('\u0000'+number);System.out.println("The character for ASCII code " + number + " is " + ch);}}

*4.9（给出字符的Unicode码）

有了上一题的折磨，没错，这一题就是那么的快乐粗暴加简单(●'◡'●)

知识点：

ASCII码的‘字符’转换为对应的‘十进制数’的方法：（字符+十进制数）！！！

对比了一哈，好像都一样。〒_〒

import java.util.Scanner;public class C9 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter a character :");String s=input.nextLine();input.close();char ch=s.charAt(0);int a=ch+0;System.out.println("The Unicode for the character " + ch + " is " + a);}}

*4.10（猜测生日）

略

*4.11（十进制转十六进制）

import java.util.Scanner;public class C11 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter a decimal value (0 to 15) :" );int number=input.nextInt();input.close();if(number>=0 && number<=15) {if(number>9) {String s = null;switch(number) {case 10:s="A";break;case 11:s="B";break;case 12:s="C";break;case 13:s="D";break;case 14:s="E";break;case 15:s="F";break;}System.out.println(" The hex value is " + s );}else {String s=""+number;System.out.println(" The hex value is " + s );}}else {System.out.println(" "+ number + " is an invalid input ");}}}

4.12（十六进制转二进制）

import java.util.Scanner;public class C12 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("Enter a hex digit: ");String s=input.nextLine();input.close();char ch=s.charAt(0);if(ch>='0' && ch<='9') {int number= ch + 0 ;int remainder1=number%2;//求得第1个余数int remainder2=number/2%2;//求得第2个余数int remainder3=number/2/2%2;//求得第3个余数int remainder4=number/2/2/2%2;//求得第4个余数System.out.println("The binary value is " + remainder4 + remainder3 + remainder2 + remainder1);}else if(ch>='A' && ch<='F') {int number=0;switch(ch) {case 'A': number += 10;break;case 'B': number += 11;break;case 'C': number += 12;break;case 'D': number += 13;break;case 'E': number += 14;break;case 'F': number += 15;break;}int remainder1=number%2;//求得第1个余数int remainder2=number/2%2;//求得第2个余数int remainder3=number/2/2%2;//求得第3个余数int remainder4=number/2/2/2%2;//求得第4个余数System.out.println("The binary value is " + remainder4 + remainder3 + remainder2 + remainder1);}else {System.out.println(ch+" is an invalid input ");}}}

*4.13（判断元音还是辅音）

import java.util.Scanner;public class C13 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter a letter: ");String s=input.nextLine();input.close();char ch=s.charAt(0);if(ch>='A' && ch<='Z' || ch>='a' && ch<='z') {if(ch=='A'|| ch=='E'|| ch=='I'|| ch=='O'|| ch=='U'|| ch=='a'|| ch=='e'|| ch=='i'|| ch=='o'|| ch=='u') {System.out.println(ch+" is a vowel");}else {System.out.println(ch+" is a consonant");}}else {System.out.println(ch + " is an invalid input");}}}

*4.14（转换字母等级为数字）

import java.util.Scanner;public class c14 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter a letter grade: ");String s=input.nextLine();input.close();char ch=s.charAt(0);if(ch>='A' && ch<='D' || ch=='F') {int number=0;switch(ch) {case 'A':number+=4;break;case 'B':number+=3;break;case 'C':number+=2;break;case 'D':number+=1;break;case 'F':number+=0;break;}System.out.println("The numeric value for grade "+ch+" is "+number);}else {System.out.println( ch + " is an invalid grade");}}}

*4.15（电话键盘）

import java.util.Scanner;public class C15 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter a letter: ");String s=input.nextLine();input.close();char ch=s.charAt(0);if(Character.isLetter(ch)) {String s1=""+ch;if(s1.equalsIgnoreCase("a") || s1.equalsIgnoreCase("b")|| s1.equalsIgnoreCase("c") ) {System.out.println("The corresponding number is " + 2 );}else if(s1.equalsIgnoreCase("d") || s1.equalsIgnoreCase("e")|| s1.equalsIgnoreCase("f") ) {System.out.println("The corresponding number is " + 3 );}else if(s1.equalsIgnoreCase("g") || s1.equalsIgnoreCase("h")|| s1.equalsIgnoreCase("i") ) {System.out.println("The corresponding number is " + 4 );}else if(s1.equalsIgnoreCase("j") || s1.equalsIgnoreCase("k")|| s1.equalsIgnoreCase("l") ) {System.out.println("The corresponding number is " + 5 );}else if(s1.equalsIgnoreCase("m") || s1.equalsIgnoreCase("n")|| s1.equalsIgnoreCase("o") ) {System.out.println("The corresponding number is " + 6 );}else if(s1.equalsIgnoreCase("p") || s1.equalsIgnoreCase("q")|| s1.equalsIgnoreCase("r")|| s1.equalsIgnoreCase("s")) {System.out.println("The corresponding number is " + 7 );}else if(s1.equalsIgnoreCase("t") || s1.equalsIgnoreCase("u")|| s1.equalsIgnoreCase("v") ) {System.out.println("The corresponding number is " + 8 );}else if(s1.equalsIgnoreCase("w") || s1.equalsIgnoreCase("x")|| s1.equalsIgnoreCase("y")|| s1.equalsIgnoreCase("z")) {System.out.println("The corresponding number is " + 9 );}}else {System.out.println(ch + " is an invalid input");}}}

4.16（随机字符）

public class C16 {public static void main(String[] args) {int random= (int) (65 + Math.random()*26);//大写字母的十进制编码值从65~90char ch=(char) ('\u0000'+random);System.out.println("这个随机字符是： " + ch);}}

*4.17（一个月中的日期）

我在编码过程中发现的问题：

当我在控制台先输入一个整型数值，接着再输入一个字符串时：控制台好像不接收第二个字符串数据，其实是接收了“回车键”的字符串，所以显得好像没有接收数据。

解决方案：1.可以让控制台接收的数据类型都是字符串先，然后再将字符串转换为数值类型。

解决方案：2.可以创建两个Scanner对象分别接收不同的数据类型。

我下面的代码用了解决方案 1. 

import java.util.Scanner;public class C17 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter a year: ");String yearString=input.nextLine();System.out.print("Enter a month: ");String month=input.nextLine();input.close();int days=0;//将字符串转为整数int year=Integer.parseInt(yearString);//判定是否闰年boolean isLeapYear=( (year%4==0 && year%100!=0) || (year%400==0) );  switch(month) {case "Jan":days=31;break;case "Feb":	if(isLeapYear) {days=29;}else {days=28;}break;case "Mar":days=31;break;case "Apr":days=30;break;case "May":days=31;break;case "Jun":days=30;break;case "Jul":days=31;break;case "Aug":days=31;break;case "Sep":days=30;break;case "Oct":days=31;break;case "Nov":days=30;break;case "Dec":days=31;break;}  System.out.println(month +" "+ year + " has " + days +  " days");}}

*4.18 （学生的专业和状况）

import java.util.Scanner;public class C18 {public static void main(String[] args) {Scanner input =new Scanner(System.in);System.out.print("Enter two character:");String s=input.nextLine();input.close();char ch1=s.charAt(0);char ch2=s.charAt(1);int number=ch2+0;String major=null;String student=null;if((ch1=='M'||ch1=='C'||ch1=='I') && (ch2=='1'||ch2=='2'||ch2=='3'||ch2=='4')) {switch(ch1) {case 'M':major="Mathmatics";break;case 'C':major="Computer Science";break;case 'I':major="Information Technology";break;}switch(ch2) {case '1':student="Freshman";break;case '2':student="Sophomore";break;case '3':student="Junior";break;case '4':student="Senior Student";break;}System.out.println(major+" "+student);}else {System.out.println("Invalid input");}}}

4.19（商业：检测ISBN-10）

略

4.20（字符串处理）

import java.util.Scanner;public class C20 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("请输入一个字符串： ");String s=input.nextLine();int length=s.length();char ch1=s.charAt(0);System.out.println("该字符串的长度为： "+length);System.out.println("该字符串的第一个字符为： "+ch1);}}

 *4.21（检查子串）

import java.util.Scanner;public class C21 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter a SSN: ");String s=input.nextLine();input.close();if(s.length()==11) {if(Character.isDigit(s.charAt(0)) && Character.isDigit(s.charAt(1)) && Character.isDigit(s.charAt(2)) && (s.charAt(3)=='-')&& Character.isDigit(s.charAt(4)) && Character.isDigit(s.charAt(5)) && (s.charAt(6)=='-') && Character.isDigit(s.charAt(7)) && Character.isDigit(s.charAt(8)) && Character.isDigit(s.charAt(9)) && Character.isDigit(s.charAt(10)) ) {System.out.println(s+" is a valid social security number");}else {System.out.println(s+" is an invalid social security number");}}else {System.out.println(s+" is an invalid social security number");}}}

4.22（检测子串）

知识点：用字符串里的 s1.contain（s2） 方法：如果S2是s1字符串的子字符串，返回true。

import java.util.Scanner;public class C22 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter string s1: ");String s1=input.nextLine();System.out.print("Enter string s2: ");String s2=input.nextLine();input.close();if(s1.contains(s2)) {System.out.println(s2+" is a substring of "+s1);	}else{System.out.println(s2+" is not a substring of "+s1);}}}

*4.23（财务应用：酬金）

import java.util.Scanner;public class C23 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter employee's name:");String name=input.nextLine();System.out.print("Enter number of hours worked in a week:");double hour=input.nextDouble();System.out.print("Enter hourly pay rate:");double payRate=input.nextDouble();System.out.print("Enter federal tax withholding rate:");double federalRate=input.nextDouble();System.out.print("Enter state tax withholding rate:");double stateRate=input.nextDouble();input.close();double grossPay=hour*payRate;System.out.printf("Employee Name: %s \n"+ "Hours Worked: %3.1f \n"+"Pay Rate: $%4.2f \n"+"Gross Pay: $%4.1f \n"+"Deductions: \n"+"  Federal Withholding (%4.1f%%): $%4.1f \n"+"  State Withholding (%3.1f%%): $%4.2f \n"+"  Total Dedution: $%5.2f \n"+"Net Pay: $%5.2f ", name, hour, payRate, grossPay, federalRate*100, federalRate*grossPay, stateRate*100, stateRate*grossPay, federalRate*grossPay+stateRate*grossPay, grossPay-(stateRate*grossPay+federalRate*grossPay) );}}

*4.24（对三个城市排序）

import java.util.Scanner;public class C24 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.print("Enter the first city: ");String city1=input.nextLine();System.out.print("Enter the second city: ");String city2=input.nextLine();System.out.print("Enter the third city: ");String city3=input.nextLine();if(city1.compareTo(city2)>0) {//System.out.println("The order is city2, city1.");if(city2.compareTo(city3)>0) {System.out.println("The three cities in alphabetical order are "+city3+", "+city2+", "+city1);}else if(city2.compareTo(city3)<0) {if(city1.compareTo(city3)<0) {System.out.println("The three cities in alphabetical order are "+city2+", "+city1+", "+city3);}else if(city1.compareTo(city3)>0){System.out.println("The three cities in alphabetical order are "+city2+", "+city3+", "+city1);}}}else if (city1.compareTo(city2)<0){//System.out.println("The order is city1, city2.");if(city1.compareTo(city3)>0) {System.out.println("The three cities in alphabetical order are "+city3+", "+city1+", "+city2);}else if(city1.compareTo(city3)<0) {if(city2.compareTo(city3)>0) {System.out.println("The three cities in alphabetical order are "+city1+", "+city3+", "+city2);}else if(city2.compareTo(city3)<0){System.out.println("The three cities in alphabetical order are "+city1+", "+city2+", "+city3);}}}}}

*4.25（生成车牌号码）

public class C25 {public static void main(String[] args) {//产生3个随机大写字母 和 4个随机数字char ch1=(char) (65+Math.random()*26);char ch2=(char) (65+Math.random()*26);char ch3=(char) (65+Math.random()*26);int number=(int) (1000+Math.random()*9000);System.out.println("一个随机的车牌号是： "+ch1+ch2+ch3+number);}}

*4.26（财务应用：货币单位）

略