打印质数、随机字母、打印菱形、闰年闰月
- 1——100求和
//方法一:
public class Demo { public static void main(String[] args) { int result = 0; for (int i=0; i<101; i++) { result += i; } System.out.println(result); } }
//方法二: public class Demo { public static void main(String[] args) { int sum = sum(100); System.out.println(sum); } static int sum(int n) { if (n==0) { return 0; } return n+sum(n-1); } }
- 1——100偶数和
//方法一: public class Demo { public static void main(String[] args) { int result = 0; for (int i=0; i<101; i=i+2) { result += i; } System.out.println(result); } }
//方法二: public class Demo { public static void main(String[] args) { int sum = sum(100); System.out.println(sum); } static int sum(int n) { if (n==0) { return 0; } return n+sum(n-2); } }
- 1——100的质数
public class Demo {
public static void main(String[] args) {
for (int i = 1; i < 101; i++) {
boolean flag = true;
if (i == 1) {
continue;
}
for (int j = 2; j < i; j++) {
if (i % j == 0) {
flag = false;
break;
}
}
if (flag) {
System.out.println(i);
}
}
}
}
- 1——100 的合数
public class Demo { public static void main(String[] args) { for (int i = 1; i < 101; i++) { boolean flag = true; if (i == 1) { continue; } for (int j = 2; j < i; j++) { if (i % j == 0) { flag = false; break; } } if (!flag) {//只改这一个地方就好了 System.out.println(i); } } } }
- 生成大小写随机字母
package HelloWorld;
public class HelloWorld {
public static void main(String[] args) {
char random;
do {
random = (char) (Math.random() * 1000 + 65);
} while (random > 122 ||( random > 90 & random < 98));
System.out.println(random);
}
}
- 打印菱形
public static void main(String[] args) { for (int i=0; i<20; i++) { for (int w=20; w>0; w--) { System.out.print(" "); } for (int k=19; k>i; k--) { System.out.print(" "); } for (int j=0; j<i+1; j++) { System.out.print("*"); } for (int h=0; h<i; h++) { System.out.print("*"); } System.out.println(); } for (int i=0; i<19; i++) { for (int w=20; w>0; w--) { System.out.print(" "); } for (int j=0; j<i+1; j++) { System.out.print(" "); } for (int k=19; k>i+0; k--) { System.out.print("*"); } for (int h=0; h<18-i; h++) { System.out.print("*"); } System.out.println(); } }
- 平年闰年每月多少天
public class Test { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); while (true) { System.out.println("请输入一个年份"); int year = scanner.nextInt(); if (year == -1) { close(scanner); break; } System.out.println("请输入一个月份"); int month = scanner.nextInt(); if (year == -1) { close(scanner); break; } boolean leapYear = (year % 4 == 0 && year % 100 != 0) || year % 400 == 0; if (leapYear) { System.out.print(year + "年是闰年,"); if (month == 2) month = 0; } else { System.out.print(year + "年是平年,"); } switch (month) { case 0: System.out.println("2月有" + "29天"); break; case 2: System.out.println(month + "月有" + "28天"); break; case 4: case 6: case 9: case 11: System.out.println(month + "月有" + "30天"); break; default: System.out.println(month + "月有" + "31天"); } } } public static void close(Scanner scanner) { scanner.close(); System.err.println("程序退出!"); } }