【java】第6章方法测试题（作业部分）

╰+攻爆jí腚メ 2022-11-14 13:29 153阅读 0赞

### 文章目录 ###

*   *  6.2
     *  6.3
     *  6.13
     *  6.18
     *  6.23
     *  6.28
     *  6.29

## 6.2 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1ODc4Mjky_size_16_color_FFFFFF_t_70]

package wwr;
    //6.2
    import java.util.Scanner;
    public class Demo {
        
    	
    	public static int sumDigits(long n)
    	{
        
    		long sum = 0;
    		while(n > 0)
    		{
        
    			sum += (n % 10);
    			n /= 10;
    		}
    		return (int)sum;
    	}
    	public static void main(String[] args) {
        
    		Scanner input = new Scanner(System.in); 
    		System.out.print("Please inpute a integer: ");
    		long num = input.nextInt();
    		System.out.print(sumDigits(num));
    	}
    
    }

## 6.3 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1ODc4Mjky_size_16_color_FFFFFF_t_70 1]

package wwr;
    //6.3
    import java.util.Scanner;
    public class Demo {
        
    	
    	public static int reverse(int number)
    	{
        
    		int tmp = 0;
    		while(number > 0)
    		{
        
    			tmp *= 10;
    			tmp += (number % 10);
    			number /= 10;
    		}
    //		System.out.println(tmp);
    		return tmp;
    	}
    	public static boolean isPalindrome(int number)
    	{
        
    		if(number == reverse(number))
    			return true;
    		else
    			return false;
    	}
    	public static void main(String[] args) {
        
    		Scanner input = new Scanner(System.in); 
    		System.out.print("Please inpute a integer: ");
    		int num = input.nextInt();
    		if(isPalindrome(num))
    			System.out.print(num + " is a palindrome");
    		else
    			System.out.print(num + " is not a palindrome");
    	}
    
    }

## 6.13 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1ODc4Mjky_size_16_color_FFFFFF_t_70 2]  
【注】  
1、eclipse光标变成黑块，是因为不小心按了`Insert`，再按一次就回来了QAQ  
![在这里插入图片描述][20210330084934304.png]  
2、java也可以用C里面的printf，制表控制输出格式就比较方便了

package wwr;
    //6.13
    import java.util.Scanner;
    public class Demo {
        
    	
    	public static double m(int i)
    	{
        
    		double ans = 0;
    		for(int j = 1; j <= i; j++)
    		{
        
    			double k = (double)j;
    			ans += k / (k + 1);
    		}
    		return ans;
    	}
    
    	public static void main(String[] args) {
        
    		System.out.println("i		m(i)");
    		System.out.println("——————————————————————");
    		for(int i = 1; i <= 20; i++)
    		{
        
    			if(i < 10)
    				System.out.print(" ");
    			System.out.print(i);
    			System.out.printf("%20.4f\n", m(i));
    		}
    	}
    
    }

![在这里插入图片描述][20210330092415386.png]

## 6.18 ##

![在这里插入图片描述][20210329194556930.png]

package wwr;
    //6.18
    import java.util.Scanner;
    public class Demo {
        
    	
    	public static boolean check(String s)
    	{
        
    		int num = 0;
    		if(s.length() != 8)
    			return false;
    		for(int i = 0; i < s.length(); i++)
    		{
        
    			if(num < 2 && '0' <= s.charAt(i) && s.charAt(i) <= '9')
    				num++;
    			else if((s.charAt(i) < 'a' || 'z' < s.charAt(i)) &&
    					(s.charAt(i) < 'A' || 'Z' < s.charAt(i)))
    				return false;
    		}
    		if(num < 2)
    			return false;
    		return true;
    	}
    	public static void main(String[] args) {
        
    		Scanner input = new Scanner(System.in);
    		System.out.print("Please inpute a Password: ");
    		String s = input.nextLine();
    		if(check(s))
    			System.out.print("Valid Password");
    		else
    			System.out.print("Invalid Password");
    	}
    
    }

## 6.23 ##

![在这里插入图片描述][20210329194643460.png]  
【注】char类型输入：没有`nextChar`！！！  
要用`char c = input.next().charAt(0);`

package wwr;
    //6.23
    import java.util.Scanner;
    public class Demo {
        
    	
    	public static int count(String str, char a)
    	{
        
    		int num = 0;
    		for(int i = 0; i < str.length(); i++)
    		{
        
    			if(str.charAt(i) == a)
    				num++;
    		}
    		return num;
    	}
    	public static void main(String[] args) {
        
    		Scanner input = new Scanner(System.in);
    		System.out.println("Please inpute a string and a character: ");
    		String s = input.nextLine();
    		char c = input.next().charAt(0);
    		System.out.print(count(s, c));
    	}
    	
    }

## 6.28 ##

![在这里插入图片描述][20210329194655165.png]  
【注】梅森素数  
（当long都是int的时好像没法输出31？？？？？

package wwr;
    //6.28
    import java.util.Scanner;
    public class Demo {
        
    	
    	public static boolean Prime(long n)
    	{
        
    		boolean flag = false;
    		long b = (long)Math.sqrt(n);
    		for(long i = 2; i <= b; i++)
    		{
        
    			if(n % i == 0)
    				return false; 
    		}
    		return true;
    	}
    	public static long Mersenne(long p)
    	{
        
    		return (long)Math.pow(2, (double)p) - 1;
    	} 
    	public static void main(String[] args) {
        
    		System.out.println("p		2^p-1");
    		System.out.println("——————————————————————————");
    		for(long i = 2; i <= 31; i++)
    		{
        
    			
    			long tmp = Mersenne(i); 
    			if(Prime(tmp))
    				System.out.println(i + "		" + tmp);
    		}
    	}
    	
    }

![在这里插入图片描述][20210330104146441.png]

## 6.29 ##

![在这里插入图片描述][20210329194712997.png]

package wwr;
    //6.29
    import java.util.Scanner;
    public class Demo {
        
    	
    	public static boolean Prime(long n)
    	{
        
    		boolean flag = false;
    		long b = (long)Math.sqrt(n);
    		for(long i = 2; i <= b; i++)
    		{
        
    			if(n % i == 0)
    				return false; 
    		}
    		return true;
    	}
    	public static void main(String[] args) {
        
    		for(long i = 3; i <= 1000; i++)
    		{
        
    			if(Prime(i) && Prime(i + 2))
    				System.out.println("(" + i + ", " + (i + 2) + ")");
    		}
    	}
    	
    }

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1ODc4Mjky_size_16_color_FFFFFF_t_70]: /images/20221022/181c6a8132c140329e3cd70099042031.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1ODc4Mjky_size_16_color_FFFFFF_t_70 1]: /images/20221022/58c25c96ca16492aa0491f5c87d012b0.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1ODc4Mjky_size_16_color_FFFFFF_t_70 2]: /images/20221022/dc80ca8df0eb4f95956b4913039b7641.png
[20210330084934304.png]: /images/20221022/44dfe4544e7d4259a9846ef2a70885b1.png
[20210330092415386.png]: /images/20221022/77e9f92dd1ba42feb6357ed786dd997f.png
[20210329194556930.png]: /images/20221022/7bf01a3f87024e15b47bfcd38074fcd5.png
[20210329194643460.png]: /images/20221022/09fb2cdc88094b96963dab410c074294.png
[20210329194655165.png]: /images/20221022/938c2dc3e0444fdca08db6d31b5381e9.png
[20210330104146441.png]: /images/20221022/cf996cd50f1741b7b95028f6e2dd52a3.png
[20210329194712997.png]: /images/20221022/4808ac03d5e64afdba5f90a40299f434.png