练习1

根据年龄, 来打印出当前年龄的人是少年(低于18), 青年(19-28), 中年(29-55), 老年(56以上)

import java.util.Scanner;public class Age {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n = sc.nextInt();if(n <= 18) {System.out.println("少年");} else if(n <= 28) {System.out.println("青年");} else if(n <= 55) {System.out.println("中年");} else {System.out.println("老年");}sc.close();}
}

练习2

判定一个数字是否是素数

import java.util.Scanner;public class PrimeNumber {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n = sc.nextInt();int i = 2;boolean a = true;while(i <= n/2) {if(n%i == 0) {a = false;break;}}if(a) {System.out.println(n+"是素数");} else {System.out.println(n+"不是素数");}sc.close();}
}

练习3

打印 1 - 100 之间所有的素数

public class PrintPrime {public static void main(String[] args) {int n = 1;for(n = 1;n <= 100;n++) {int i = 2;boolean a = true;while(i <= n/2) {if(n%i == 0) {a = false;break;}i++;}if(a) {System.out.print(n+" ");}}}
}

练习4

输出 1000 - 2000 之间所有的闰年

public class LeapYear {public static void main(String[] args) {int a = 1000;for(a = 1000;a < 2000;a++) {if(a%100 == 0) {if(a%400 == 0) {System.out.println(a+"是闰年");}} else if(a%4 == 0) {System.out.println(a+"是闰年");}}}
}

练习5

输出乘法口诀表

public class MultiplicationTable {public static void main(String[] args) {int i = 0;int j = 0;for(i = 1;i <= 9;i++) {for(j = 1;j <= i;j++) {System.out.printf("%d*%d=%d ",j,i,i*j);}System.out.println();}}
}

练习6

求两个正整数的最大公约数

import java.util.Scanner;public class CommonDivisor {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int a = sc.nextInt();int b = sc.nextInt();boolean con = true;int c = 1;for( c = a<b?a:b;c>1;c--) {if(a%c == 0&&b%c == 0) {System.out.println(c+"为最大公约数");con = false;break;}}if(con) {System.out.println("没有公约数");}}
}

练习7

求出0～999之间的所有“水仙花数”并输出。(“水仙花数”是指一个三位数，其各位数字的立方和确好等于该数本身，

如： 153＝1^3＋5^3＋3^3 ，则153是一个“水仙花数”。)

public class NarcissisticNumber {public static void main(String[] args) {int i = 1;int x = 0;double w = 1.0;for(i = 0;i<1000;i++) {x = 0;double p = Math.pow(10.0,w);while (i/Math.pow(10.0,w) > 1) {p = i/Math.pow(10.0,w);w++;}int j = i;while (j>0) {x += Math.pow(j%10,w);j /= 10;}if (x == i) {System.out.println(i);}}}
}

练习8

写一个函数返回参数二进制中 1 的个数，比如： 15 0000 1111 4 个 1

import java.util.Scanner;public class BinarySystem {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n = sc.nextInt();int count = 0;while ( n != 0) {if ((n&1) == 1) {count++;}n >>= 1;}System.out.println(count);sc.close();}
}

练习9

获取一个数二进制序列中所有的偶数位和奇数位，分别输出二进制序列

import java.util.Scanner;public class BinarySequence {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n = sc.nextInt();int j = n;int o = n;int i = 0;while(i < 16) {System.out.print(j&1);j >>= 2;i++;}System.out.println();o >>= 1;i = 0;while(i < 16) {System.out.print(o&1);o >>= 2;i++;}}
}