目录

一、整数位数的判断

二、水仙花数及判断

三、质数输出及判断质数

 四、完全数的输出及判断

五、九九乘法表

提示：以下是本篇文章正文内容，下面案例可供参考

一、整数位数的判断

package ch1;

import java.util.Scanner;

public class 整数位数的判断 {
    public static void main(String[] args) {
        System.out.println("请输入整数");
        Scanner in = new Scanner(System.in);
        int num,amount=0;
        num = in.nextInt();
        while  (num>0){
            num = num/10;
            amount = amount + 1;
        }
        System.out.println("整数位数为："+amount);
    }
}

 

二、水仙花数及判断

package ch1;
import java.util.*;
public class 水仙花 {
    public static void main(String[] args) {
        for(int i = 100; i <= 999; i++){
            int a=i/100;
            int b=i%100/10;
            int c=i%10;
            if(a*a*a+b*b*b+c*c*c == i){
                System.out.println("水仙花数为"+i);
            }
        }
    }
}

package ch1;
import java.util.Scanner;

public class 判断水仙花 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("请输入一个三位数：");
        int num = sc.nextInt();
        int g = num%10;      //得到个位数
        int s = (num/10)%10; //得到十位数
        int b = num/100;     //得到百位数
        int sum = (g*g*g)+(s*s*s)+(b*b*b);  //得到总和
        //判断是否相等
        if(sum == num){      //若相等
            System.out.println("该数为水仙花数！");
        }else                //若不等
            System.out.println("该数不为水仙花数！");
    }
}

 

三、质数输出及判断质数

package ch1;

public class 质数输出 {
    public static void main(String[] args) {
        for (int i = 2; i <= 100000; i++) { //最小的质数是2
            int j = 2; //从2开始，到i-1为止，没有i的因子
            while (j <= i - 1) {
                if (i % j == 0) {
                    break;
                }
                j++;
            }
            if (j == i) { //说明if根本没进去过，即：不存在其他因子
                System.out.println(i);
            }
        }
    }
}

package ch1;

import java.util.Scanner;

public class 质数判断 {
        public static void main(String[] args) {
            boolean isFlag = true;
            Scanner sc = new Scanner(System.in);
            System.out.println("请输入一个正整数");
            int num = sc.nextInt();
            if (num > 0) {
                int k = (int) Math.sqrt(num);//k为num的正平方根，取整数
                for (int i = 2; i <= k; i++) {
                    if (num % i == 0) {
                        isFlag = false;//不是素数
                        break;
                    }
                }
            }
            if (isFlag) {
                System.out.println(num + "是素数");
            } else {
                System.out.println(num + "不是素数");
            }
        }
    }

 

 四、完全数的输出及判断

package ch1;

public class 完全数 {
    public static void main(String[] args) {
        int i,j;
        System.out.println("一千以内的完全数");
        for(i=1;i<=10000;i++){
            int sum = 0;
            for(j=1;j 
package ch1;

import java.util.Scanner;
public class 判断完全数 {
    public static void main(String[] args) {
        System.out.println("请输入：");
        Scanner in = new Scanner(System.in);
        int i = in.nextInt();
            int sum = 0;
            for (int j = 1; j < i; j++) {
                if (i % j == 0)
                    sum += j;
            }
            if (sum == i)
                System.out.println("该数是完全数");
            else
                System.out.println("该数不是完全数");

        }
    }

 
 
 
五、九九乘法表 
package ch1;

public class 九九乘法表 {

        public static void main(String[] args) {
            for (int i = 1; i <= 9; i++) {
                for (int j = 1; j <= i; j++) {
                    System.out.print(i+"*"+j+"="+j*i+"	");
                }
                System.out.print("n");
            }
        }

    }