java第二次上机作业

P130，4.16

package gsn;

 

publicclass sdfg {

 

    publicstaticvoid main(String[] args) {

        // TODO Auto-generated method stub

        //int number=new int;

        int number = (int)(Math.random()*26)+65;

        System.out.println((char)number);

           

 

    }

 

}

 

P2367.7

package gsn;

 

importjava.util.Random;

 

publicclass sdfg {

 

    publicstaticvoid main(String[] args) {

        // TODO Auto-generated method stub

        //int number=new int;

        int number = (int)(Math.random()*10);

        System.out.println(number);

        int counts[]=newint[10];

        Randomrandom=new Random();

       

        for(int i=0;i<=100;i++)

        {

            counts[random.nextInt(10)]++;

        }

        for(int i=0;i<10;i++)

        {

            System.out.println(i+"出现次数"+counts[i]);

        }

 

    }

 

}

 

P202 6.23

package gsn;

 

importjava.util.Scanner;

publicclass sdfg {

   

    publicstaticint counts(String str,char a){

        int count=0;

       

        for(int i=0;i<str.length();i++)

        {

            if(str.charAt(i)==a){

                count++;

            }

        }

        return count;

       

    }

 

    publicstaticvoid main(String[] args) {

        // TODO Auto-generated method stub

        //int number=new int;

        Scanner input =new Scanner(System.in);//create a scanner

        System.out.println("input the string and a char:");

        String str=input.nextLine();

        char a=input.next().charAt(0);//the first one

        System.out.println(counts(str,a));//带参数的

       

       

    }      

}

 

P203 6.28

packagesushu;

publicclass sf{

 publicstaticvoid main(String[] args){

     System.out.println("p  2^p-1");

     System.out.println("------------");

 

     for(intp=2;p<=31;p++)

        {

            intnumber=(int) (Math.pow(2, p)-1);//调用prime（int number）方法，返回true，进行打印操作。

            if(prime(number))

            {

                System.out.println(p+"     "+number);

            }

        }

    }

   

    publicstaticboolean prime(intnumber)//判断p是否是质数的方法

    {

        for(inti=2;i<=Math.sqrt(number);i++)

        {

            if(number%i==0)

            {

                returnfalse;

            }

        }

        returntrue;

    }

 

}