初入java4

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小结:

   学了这么多天的java,终于还是学会了写一些简单的小程序:

 

1.回文数,例:12321(123321)

 

package random;

 

import java.util.Scanner;

 

public class HomeWork1 {

 

       public static void main(String[] args) {

 

              //判断回文数12321

 

              Scanner sc = new Scanner(System.in);

 

              System.out.println("请输入一个数:");

 

              int num = sc.nextInt();

 

              int num1 = num;

 

              int sum = 0;

 

              int wei = 1;

 

              while(num/10!=0){

 

                     wei++;

 

                     num /= 10;

 

              }

 

              int a[] = new int[wei];

 

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

 

                     a[i] = num1 % 10;

 

                     num1 /= 10;

 

              }

 

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

 

                     if(a[i]==a[a.length-1-i]){

 

                            sum++;

 

                     }

 

              }

 

              if(sum==a.length){

 

                     System.out.println("这是一个回文数");

 

              }

 

              sc.close();

 

       }

 

}

 

2.练习随机数

 

例ran.nextInt(20)+10

 

相当于0~19都加10得10~29的数

 

随机产生50——111的数

 

       -11——32的数

 

package random;

 

import java.util.Random;

 

public class HomeWork2 {

 

       public static void main(String[] args) {

 

              //随机数输出

 

              Random ran = new Random();

 

              int num1 = 0;

 

              for(int i = 1;i<=10;i++){

 

                     num1 = ran.nextInt(20)+10;

 

                     System.out.print(num1+" ");

 

              }

 

              int num2 = 0;

 

              System.out.println();

 

              for(int i = 1;i<=10;i++){

 

                     num2 = ran.nextInt(62)+50;

 

                     System.out.print(num2+" ");

 

              }

 

              int num3 = 0;

 

              System.out.println();

 

              for(int i = 1;i<=10;i++){

 

                     num3 = ran.nextInt(44)-11;

 

                     System.out.print(num3+" ");

 

              }

 

       }

 

}

 

3.定义一个int型的一维数组,包含10个元素,分别赋一些随机整数,然后求出所有元素的最大值,

 

最小值,平均值,和,并输出出来

 

package random;

 

import java.util.Random;

 

public class HomeWork3 {

 

       public static void main(String[] args) {

 

              //求随机输入的十个数字的最大值,最小值,和,以及平均数

 

              Random ran = new Random();

 

              int a[] = new int[10];

 

              int num = 0;

 

              int sum = 0;

 

              double avr = 0.0;

 

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

 

                     num = ran.nextInt(10)+1;

 

                     a[i] = num;

 

                     sum += a[i];

 

                     System.out.print(a[i]+"  ");

 

              }

 

              avr = sum / 10;

 

              System.out.println();

 

              System.out.println("十个数字的和为:"+sum);

 

              System.out.println("十个数字的平均值为:"+avr);

 

              int min = a[0];

 

              int max = a[0];

 

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

 

                     if(a[i]<min){

 

                            min = a[i];

 

                     }

 

              }

 

              System.out.println("十个数字中最小的为:"+min);

 

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

 

                     if(a[i]>max){

 

                            max = a[i];

 

                     }

 

              }

 

              System.out.println("十个数字中最大的为:"+max);

 

       }

 

}

 

4.定义一个int型的一维数组,包含10个元素,分别赋值为1—10, 然后将数组中的元素都向前移一个位置,

 

即,a[0]=a[1],a[1]=a[2],…最后一个元素的值是原来第一个元素的值,然后输出这个数组

 

package random;

 

import java.util.Random;

 

public class HomeWork4 {

 

       public static void main(String[] args) {

 

              //随机输入十个数,将a[0]=a[1],依次输出

 

              Random ran = new Random();

 

              int a[] = new int[10];

 

              int num = 0;

 

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

 

                     num = ran.nextInt(10)+1;

 

                     a[i] = num;

 

                     System.out.print(a[i]+" ");

 

              }

 

              System.out.println();

 

              int temp = a[0];

 

              for(int i = 0;i<a.length-1;i++){

 

                     a[i] = a[i+1];

 

                     System.out.print(a[i]+" ");

 

              }

 

              a[9] = temp;

 

              System.out.print(a[9]);

 

       }

 

}

 

5.打印出101—200(包括101与200)之间有多少个素数

 

package second;

 

public class HomeWork1 {

 

       public static void main(String[] args) {

 

              //101-200之间素数的个数

 

              int i = 2;

 

              int num = 101;

 

              int j = 0;

 

              for(num=101;num<=200;num++){

 

                     for(i=2;i<=num;i++){

 

                            if(num%i==0)

 

                            {

 

                                   break;

 

                            }

 

                     }

 

                     if(i==num)

 

                     {

 

                            j++;

 

                     }

 

              }

 

              System.out.println(j);

 

       }

 

}

 

6.斐波那契数列

 

1 1 2 3 5 8 13 21...按顺序求出第20个数

 

package second;

 

public class HomeWork2 {

 

       public static void main(String[] args) {

 

              //斐波那契数列

 

              int a = 0;

 

              int num = 1;

 

              int b = 1;

 

              int c = 0;

 

              for(num=1;num<=20;num++){

 

                     c = a + b;

 

                     b = a;

 

                     a = c;

 

                     System.out.println(a);

 

              }

 

       }

 

}

 

7.使用辗转相除法求出两个数字的最大公约数

 

package second;

 

import java.util.Scanner;

 

public class HomeWork3 {

 

       public static void main(String[] args) {

 

              //随意输出两个数,求出两个数的最大公约数

 

              Scanner sc = new Scanner(System.in);

 

              int yushu = 0;

 

              int num1 = 0,num2 = 0;

 

              for(;;){

 

                     System.out.println("请输入第一个数:");

 

                     num1 = sc.nextInt();

 

                     System.out.println("请输入第二个数:");

 

                     num2 = sc.nextInt();

 

                     if(num1 == 0||num2 == 0){

 

                            continue;

 

                     }

 

                     else{

 

                            break;

 

                     }

 

              }

 

              while(num2!=0)

 

              {

 

                     yushu = num1 % num2;

 

                     num1 = num2;

 

                     num2 = yushu;

 

              }

 

              System.out.println(num1);

 

              sc.close();

 

       }

 

}

 

8.随意输入两个数字,并求出最小公倍数

 

package second;

 

import java.util.Scanner;

 

public class HomeWork4 {

 

       public static void main(String[] args) {

 

              //随意输出两个数,求出两个数的最小公倍数

 

              Scanner sc = new Scanner(System.in);

 

              System.out.println("请输入第一个数:");

 

              int num1 = sc.nextInt();

 

              System.out.println("请输入第一个数:");

 

              int num2 = sc.nextInt();

 

              int num = 1;

 

              for(num=1;num<=num1*num2;num++){

 

                     if(num%num1==0&num%num2==0){

 

                            System.out.println("他们的最小公倍数为:"+num);

 

                            break;

 

                     }

 

              }

 

              sc.close();

 

       }

 

}

 

9.算出1-10000

 

如果一个数恰好等于它的因子之和,则称该数为“完全数”

 

例:6,它有约数1、2、3、6,除去它本身6外,其余3个数相加,

 

1+2+3=6。

 

package second;

 

public class HomeWork5 {

 

       public static void main(String[] args) {

 

              //输出1-10000之间的完数

 

              int num = 0;

 

              int num1 = 0;

 

              int sum = 0;

 

              for(num=1;num<=10000;num++){

 

                     sum = 0;

 

                     for(num1=1;num1<num;num1++){

 

                            if(num%num1==0){

 

                                   sum +=num1;

 

                            }

 

                     }

 

                     if(sum==num){

 

                            System.out.println(num);

 

                     }

 

              }

 

       }

 

}

 

10.输入随机一个日期判断是该年哪一天(输入年、月、日三个数字)

 

       public static void main(String[] args) {

 

              System.out.println("请输入是哪一年");

 

              Scanner sc = new Scanner(System.in);

 

              int year = sc.nextInt();

 

              System.out.println("请输入是哪一月");

 

              int month = sc.nextInt();

 

              System.out.println("请输入是哪一天");

 

              int day = sc.nextInt();

 

              switch (month) {

 

              case 12:

 

                     day += 30;

 

              case 11:

 

                     day += 31;

 

              case 10:

 

                     day += 30;

 

              case 9:

 

                     day += 31;

 

              case 8:

 

                     day += 31;

 

              case 7:

 

                     day += 30;

 

              case 6:

 

                     day += 31;

 

              case 5:

 

                     day += 30;

 

              case 4:

 

                     day += 31;

 

              case 3:

 

                     day += 28;

 

              case 2:

 

                     day += 31;

 

              case 1:

 

                     break;

 

              default:

 

                     System.out.println("输入有误");

 

              }

 

              if ((month > 2 && year % 4 == 0 && year % 100 != 0)

 

                            || (month > 2 && year % 400 == 0)) {

 

                     day += 1;

 

              }

 

              System.out.println("这一天是该年的第" + day + "天");

 

       }

 

11.输出所有的水仙花数

 

水仙花数是指一个数3位数,其各各位数字立方和等于其本身

 

例如: 153 = 1*1*1 + 3*3*3 + 5*5*5

 

package first;

 

public class HomeWork2 {

 

       public static void main(String[] args) {

 

              //输出三位数的水仙花数

 

              int i = 0,j = 0, k = 0,l = 0;

 

              int num = 100;

 

              for(num = 100;num<=999;num++){

 

                     i = num % 10;

 

                     j = num % 100 / 10;

 

                     k = num / 100;

 

                     l = i*i*i + j*j*j + k*k*k;

 

                     if(l==num)

 

                     {

 

                            System.out.println(num);

 

                     }

 

              }

 

       }

 

}

 

12.计算圆周率(建议循环10W次以上,并注意循环的变量的数据类型)

 

PI=4-4/3+4/5-4/7+4/9.......

 

package first;

 

public class HomeWork3 {

 

       public static void main(String[] args) {

 

              //求PI

 

              double i = 1.0;

 

              double sum = 0.0;

 

              int num = 1;

 

              for(num=1;num<100000;num++){

 

                     if(num%2==0){

 

                            sum-=4/i;

 

                     }

 

                     else{

 

                            sum+=4/i;

 

                     }

 

                     i += 2;

 

              }

 

              System.out.println(sum);

 

       }

 

}

 

 

 

 

 

13.有一分数序列:2/1,3/2,5/3,8/5,13/8,21/13...求出这个数列的前20项之和

 

 

 

package first;

 

 

 

public class HomeWork4 {

 

       public static void main(String[] args) {

 

              double i = 1.0;

 

              double j = 2.0;

 

              double sum = 0;

 

              double k = 0.0;

 

              int num = 1;

 

              for(num=1;num<=20;num++){

 

                     sum+=j/i;

 

                     k=j;

 

                     j=i+j;             

 

                     i=k;

 

              }

 

              System.out.println(sum);

 

       }

 

}

 

14.菱形

 

    *

 

   * *

 

  * * *

 

 * * * *

 

* * * * *

 

 * * * *

 

  * * *

 

   * *

 

    *

 

       public static void main(String[] args) {

 

              Scanner sc = new Scanner(System.in);

 

              int num = sc.nextInt();

 

              //判断行数,打印相应行数的正三角

 

              for(int i = 0;i<num;i++){

 

                     //输出星星前的空格

 

                     for(int b = 1;b<num-i;b++){

 

                            System.out.print(" ");

 

                     }

 

                     //输入星星

 

                     for(int c = 0;c<2*i+1;c++){

 

                            System.out.print("*");

 

                     }

 

                     System.out.println();

 

              }

 

              //倒三角

 

              //行数

 

              for(int i=num-1;i>0;i--){

 

                     //空格

 

                     for(int b = 1;b<num-i+1;b++){

 

                            System.out.print(" ");

 

                     }

 

                     //星星

 

                     for(int c = 0;c<2*i-1;c++){

 

                            System.out.print("*");

 

                     }

 

                     System.out.println();

 

              }

 

              sc.close();

 

       }

 

15.猴子吃桃

 

       public static void main(String[] args) {

 

              int num = 1;

 

              for (int i = 1; i < 10; i++) {

 

                     num = (num + 1) * 2;

 

              }

 

              System.out.println("猴子第一天一共摘了"+num+"个桃");

 

       }

 

16.九九乘法表

 

package first;

 

public class Test1 {

 

       public static void main(String[] args) {

 

              int i = 1;

 

              int j = 1;

 

              while(i<=9)

 

              {

 

                     while(j<=i)

 

                     {

 

                            System.out.print(j+"*"+i+"="+j*i+"\t");

 

                            j++;

 

                     }

 

                     i++;

 

                     System.out.println();

 

              }

 

       }

 

}

 

17.1-2+3-4+5-......-100求和

 

package first;

 

import java.util.Scanner;

 

public class Test {

 

       public static void main(String[] args) {

 

              int i = 1;

 

              int sum = 0;

 

              for(i=1;i<=100;i++)

 

              {

 

                     if(i%2==0)

 

                     {

 

                            sum-=i;

 

                     }

 

                     else{

 

                            sum+=i;

 

                     }

 

              }

 

              System.out.println(sum);

 

       }

 

}

 

18.100以内奇数和

 

package first;

 

import java.util.Scanner;

 

public class Test {

 

       public static void main(String[] args) {

 

              int i = 1;

 

              int sum = 0;

 

              for(i=1;i<=100;i++)

 

              {

 

                     if(i==1|i%3==0)

 

                     {

 

                            sum+=i;

 

                     }

 

              }

 

              System.out.println(sum);

 

       }

 

}

 

19.2+1+2/3+1/2+2/5+......+1/50求和

 

       public static void main(String[] args) {

 

              double num = 2;

 

              double sum = 0;

 

              for(int i = 1;i<=100;i++){

 

                     sum+=num/i;

 

              }

 

              System.out.println(sum);

 

       }


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