原文： https://beginnersbook.com/2019/04/java-program-to-print-alternate-prime-numbers/
在本教程中，我们将编写一个 Java 程序，以显示备用素数，直到给定值。
在以下示例中，我们有两个用户定义的方法：checkPrime()和printAltPrime()。
checkPrime()方法检查作为参数传递的数字是否为素数，如果数字为素数，则此方法返回 1，否则返回false。
printAltPrime()方法打印备用素数，直到作为参数传递的值。
请阅读注释以了解程序的逻辑。
class JavaExample
{
//method for checking prime number
static int checkPrime(int num)
{
int i, flag = 0;
for(i = 2; i<= num / 2; i++)
{
if(num % i == 0)
{
flag = 1;
break;
}
}
/* If flag value is 0 then the given number num
* is a prime number else it is not a prime number
*/
if(flag == 0)
return 1;
else
return 0;
}
//Method for printing alternate prime numbers
static void printAltPrime(int n)
{
/* When the temp value is odd then we are
* not printing the prime number and when it is
* even then we are printing it, this way we are
* displaying alternate prime numbers
*/
int temp = 2;
for(int num = 2; num <= n-1; num++)
{
//checking each number whether it is prime or not
if (checkPrime(num) == 1)
{
// if temp is even then only print the prime number
if (temp % 2 == 0)
System.out.print(num + " ");
temp ++;
}
}
}
public static void main(String[] args)
{
int num = 20;
System.out.print("Alternate prime numbers upto " + num+" are: ");
printAltPrime(num);
}
}输出：
