第二章 Java语言基础（2）

1.编写一个java application,求出e=1+1/1!+1/2!+1/3!+...+1/n!+...的近似值,要求误差小于0.0001。

 

package test;

public class Test 
{         
    //求n的阶乘
    public static int fn(int n)
    {  
        if(n == 1)
        {   
            return 1;  
        }  
        return n*fn(n-1); 
    }          
    //求和 
    public static double sum(int n)
    {  
        double sum = 0;  
        for(; n!= 1; n--)
        {   
            sum = sum + (double)1/fn(n);
            //注意要强制转换成float或者double  
        }  
        return sum; 
    }  
    public static void main(String args[])
    {  
        int n = 10;  
        System.out.println(sum(n)); 
    }
    
}

 

输出：

0.7182818011463845

 

2.利用可变列数组实现乘法口诀打印

 

package test;

public class cfkj 
{
    public static void main(String[] args)
    {
        int arr[][] = new int[10][10];
        for(int i = 1;i<10;i++)
        {
            for(int j = 1;j<10;j++)
            {
                arr[i][j] = i * j;
            }
        }
        for(int i = 1;i<10;i++)
        {
            for(int j = 1;j<10;j++)
            {
                System.out.print(i+"x"+j+"="+arr[i][j] + " ");
            }
            System.out.println();
        }
    }
}

输出：

1x1=1 1x2=2 1x3=3 1x4=4 1x5=5 1x6=6 1x7=7 1x8=8 1x9=9
2x1=2 2x2=4 2x3=6 2x4=8 2x5=10 2x6=12 2x7=14 2x8=16 2x9=18
3x1=3 3x2=6 3x3=9 3x4=12 3x5=15 3x6=18 3x7=21 3x8=24 3x9=27
4x1=4 4x2=8 4x3=12 4x4=16 4x5=20 4x6=24 4x7=28 4x8=32 4x9=36
5x1=5 5x2=10 5x3=15 5x4=20 5x5=25 5x6=30 5x7=35 5x8=40 5x9=45
6x1=6 6x2=12 6x3=18 6x4=24 6x5=30 6x6=36 6x7=42 6x8=48 6x9=54
7x1=7 7x2=14 7x3=21 7x4=28 7x5=35 7x6=42 7x7=49 7x8=56 7x9=63
8x1=8 8x2=16 8x3=24 8x4=32 8x5=40 8x6=48 8x7=56 8x8=64 8x9=72
9x1=9 9x2=18 9x3=27 9x4=36 9x5=45 9x6=54 9x7=63 9x8=72 9x9=81

 

3. 输出图形

package test;

public class print 
{
     public static void main(String[] args)
     {
         System.out.println("*");
         int i,j,k;
         for(i=2;i<=8;i++)
         {
             j=i;
             while(j>0)
             {
                 k=i-1;
                 System.out.print("*");
                 while(k>0)  
                 {
                     System.out.print(".");
                     k--;
                 }
                 j--;
             }
             System.out.println();
         }
     }
}

输出：

*
*.*.
*..*..*..
*...*...*...*...
*....*....*....*....*....
*.....*.....*.....*.....*.....*.....
*......*......*......*......*......*......*......
*.......*.......*.......*.......*.......*.......*.......*.......