Java Program to Display Alternate Prime Numbers

2025年3月17日 | 阅读 3 分钟

在本节中，我们将学习如何创建Java 程序来显示交替素数。

素数：素数是指当 p 整除 ab 时，p 要么整除 a，要么整除 b。换句话说，一个只能被自身整除的数称为素数。例如，2、3、5、7 等都是素数。

在下面的程序中，我们定义了两个名为checkPrime() 和 printAlternatePrimeNumber() 的方法。

checkPrime() 方法检查传入的数字是否为素数。如果数字是素数，则返回 1，否则返回 0。

printAlternatePrimeNumber() 方法打印 up to n 的交替素数。

AlternatePrimeNumberExample1.java

public class AlternatePrimeNumberExample1
{ 
//main method
public static void main(String[] args)  
{ 
int num = 20; 
//prints alternate prime numbers
System.out.print("Alternate prime numbers up to " + num+" are: ");  
//method calling
printAlternatePrimeNumber(num); 
}
//method checks that the number is prime or not
static int checkPrime(int num) 
{ 
int i, flag = 0; 
// we have started i=2 because 2 is a known prime number
for(i = 2; i<= num / 2; i++) 
{ 
if(num % i == 0) 
{ 
flag = 1; 
break; 
} 
} 
if(flag == 0) 
return 1; 
else
return 0; 
} 
//method for printing alternate prime numbers
static void printAlternatePrimeNumber(int n) 
{ 
//if the value of temp variable is odd, we do not print the prime number
//if the value of temp variable is even, we print the prime number
int temp = 2; 
for(int num = 2; num <= n-1; num++) 
{ 
//checking the number is prime or not
if (checkPrime(num) == 1) 
{  
//prints the prime number if temp is even
if (temp % 2 == 0) 
System.out.print(num + " "); 
//increments the temp variable by 1
temp ++; 
} 
} 
} 
}

输出

Alternate prime numbers up to 40 are: 2 5 11 17 23 31

让我们看另一个显示交替素数的逻辑。

AlternatePrimeNumberExample2.java

import java.util.*;
public class AlternatePrimeNumberExample2
{
public static void main(String args[])
{
int n;
int status = 1;
int num = 3;
//object of the ArrayList class
List<Integer> primelist=new ArrayList<Integer>();
//object of the Scanner class
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the value of n: ");
//reading the value of n from the user
n = scanner.nextInt();
if (n >= 1)
{
System.out.println("First "+n+" prime numbers are: ");
//2 is a known prime number
System.out.println(2);
//adding 2 in the ArrayList
primelist.add(2);
}
for(int i = 2 ; i <=n ; )
{
for(int j = 2 ; j <= Math.sqrt(num) ; j++)
{
if(num%j == 0)
{
status = 0;
break;
}
}
if(status != 0)
{
System.out.println(num);
//adding numbers to the ArrayList
primelist.add(num);
i++;
}
status = 1;
num++;
}
System.out.println("Alternate prime numbers are:");
//loop for printing the alternate prime numbers
for(int k=0;k<primelist.size();k++)
{
if((k%2)==0)
System.out.println(""+primelist.get(k));
}
}
}

输出

Enter the value of n: 10
First 10 prime numbers are: 
2
3
5
7
11
13
17
19
23
29
Alternate prime numbers are:
2
5
11
17
23

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