《Java语言程序设计与数据结构》编程练习答案（第六章）（二）

英文名：Introduction to Java Programming and Data Structures, Comprehensive Version, 11th Edition

6.14

public class book {
       public static void main(String[] args)    {
           System.out.println("i\t\tm(i)");        System.out.println("--------------");        for(int i=1;i<=901;i+=100)            System.out.printf("%-2d\t\t%7.4f\n",i,m(i));    }    public static double m(int n)    {
           double sum = 0;        for(int i=1;i<=n;i++)        {
               if(i%2==1)                sum+=1.0/(2*i-1);            else                sum-=1.0/(2*i-1);        }        return 4.0*sum;    }}

6.15

见习题3.13

👨佛🌶

6.16

public class book {
       public static void main(String[] args)    {
           for(int i=2000;i<=2020;i++)            System.out.println(i+" has "+numberOfDyaInYear(i)+" days.");    }    public static int numberOfDyaInYear(int year)    {
           if((year%4==0&&year%100!=0)||(year%400==0))            return 366;        else            return 365;    }}

6.17

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter n: ");        int n = input.nextInt();        printMatrix(n);    }    public static void printMatrix(int n)    {
           for(int i=0;i

6.18

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input=new Scanner(System.in);        System.out.print("Enter your password: ");        String dick = input.next();        if(isValid(dick))            System.out.println("Valid Password.");        else            System.out.println("Invalid Password.");    }   public static boolean isValid(String ass)   {
          int len = ass.length();       int count=0;       if(len<8)           return false;       for(int i=0;i
   
    ='a')||(tmp<='Z'&&tmp>='A')||(tmp<='9'&&tmp>='0')) {
              }           else               return false;       }       for(int i=0;i
    
     ='0')               count++;       }       return count >= 2;   }}

6.19

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input=new Scanner(System.in);        System.out.print("Enter three sides: ");        double s1=input.nextDouble();        double s2=input.nextDouble();        double s3=input.nextDouble();        if(isValid(s1,s2,s3))            System.out.println("The area is "+area(s1,s2,s3));        else            System.out.println("The input is invalid.");    }    public static boolean isValid(            double side1,double side2,double side3    )    {
           return !(side1 >= side2 + side3) && !(side2 >= side1 + side3) && !(side3 >= side1 + side2);    }    public static double area(            double side1,double side2,double side3    )    {
           double p=(side1+side2+side3)/2.0;        double area = Math.sqrt(p*(p-side1)*(p-side2)*(p-side3));        return area;    }}

6.20

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input=new Scanner(System.in);        System.out.print("Enter a string: ");        String s = input.next();        System.out.println(s+" has "+countLetters(s)+" letters.");    }    public static int countLetters(String s)    {
           int len=s.length();        s=s.toLowerCase();        int count=0;        for(int i=0;i
   
    = 'a')                count++;        }        return count;    }}

6.21

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input=new Scanner(System.in);        System.out.print("Enter a string: ");        String s = input.next();        int len = s.length();        s=s.toUpperCase();        for(int i=0;i
   
    ='A')                System.out.print(getNumber(s.charAt(i)));            else                System.out.print(s.charAt(i));        }        System.out.print('\n');    }    public static int getNumber(char uppercaseLetter)    {
           if(uppercaseLetter=='A'||uppercaseLetter=='B'||uppercaseLetter=='C')            return 2;        else if(uppercaseLetter=='D'||uppercaseLetter=='E'||uppercaseLetter=='F')            return 3;        else if(uppercaseLetter=='G'||uppercaseLetter=='H'||uppercaseLetter=='I')            return 4;        else if(uppercaseLetter=='J'||uppercaseLetter=='K'||uppercaseLetter=='L')            return 5;        else if(uppercaseLetter=='M'||uppercaseLetter=='N'||uppercaseLetter=='O')            return 6;        else if(uppercaseLetter=='P'||uppercaseLetter=='Q'||uppercaseLetter=='R'||uppercaseLetter=='S')            return 7;        else if(uppercaseLetter=='T'||uppercaseLetter=='U'||uppercaseLetter=='V')            return 8;        else            return 9;    }}

6.22

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input=new Scanner(System.in);        System.out.print("Enter a integer: ");        long ass = input.nextLong();        System.out.println("The root is "+sqrt(ass));    }    public static double sqrt(long n)    {
           double lastGuess = 1.0;        double nextGuess = (lastGuess+n/lastGuess)/2;        while(Math.abs(lastGuess-nextGuess)>0.0001)        {
               lastGuess=nextGuess;            nextGuess=(nextGuess+n/nextGuess)/2;        }        return nextGuess;    }}

6.23

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input=new Scanner(System.in);        System.out.print("Enter the string: ");        String s = input.next();        System.out.print("Enter the char: ");        char c = input.next().charAt(0);        System.out.println("The number of "+c+" in "+s+" is "+count(s,c));    }    public static int count(String str, char a)    {
           int jb=0;        for(int i=0;i

6.24

👨🐰🌶

6.25

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input=new Scanner(System.in);        System.out.print("Enter the milliseconds: ");        long ass = input.nextLong();        System.out.println(convertMillis(ass));    }    public static String convertMillis(long millis)    {
           long s =millis/1000;        long se = s%60;        s/=60;        long min = s%60;        s/=60;        long h = s;        return h+":"+min+":"+se;    }}

6.26

public class book {
       public static void main(String[] args)    {
           int count=0;        int base=0;        int dick = 2;        while(count<100)        {
               if(isPrime(dick)&&isPalindrome(dick))            {
                   System.out.print(dick+" ");                count++;            }            if(count%10==0&&count!=base) {
                   System.out.print('\n');                base+=10;            }            dick++;        }    }    public static boolean isPrime(int n)    {
           for(int i=2;i<=n/2;i++)        {
               if(n%i==0)                return false;        }        return true;    }    public static boolean isPalindrome(int n)    {
           String ass = Integer.toString(n);        for(int i=0;i

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