# Java 程序：打印備用素數 > 原文： [https://beginnersbook.com/2019/04/java-program-to-print-alternate-prime-numbers/](https://beginnersbook.com/2019/04/java-program-to-print-alternate-prime-numbers/) 在本教程中，我們將編寫一個 Java 程序，以**顯示備用素數，直到給定值**。 ## Java 示例：打印備用素數 在以下示例中，我們有兩個用戶定義的方法：`checkPrime()`和`printAltPrime()`。 `checkPrime()`方法檢查作為參數傳遞的數字是否為素數，如果數字為素數，則此方法返回 1，否則返回`false`。 `printAltPrime()`方法打印備用素數，直到作為參數傳遞的值。 請閱讀注釋以了解程序的邏輯。 ```java 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); } } ``` **輸出：**  #### 相關的 Java 示例 1. [Java 程序：顯示前`n`個素數](https://beginnersbook.com/2014/01/java-program-to-display-first-n-or-first-100-prime-numbers/) 2. [Java 程序：檢查素數](https://beginnersbook.com/2014/01/java-program-to-check-prime-number/) 3. [Java 程序：檢查一個數字是否完美平方](https://beginnersbook.com/2019/02/java-program-to-check-if-given-number-is-perfect-square/) 4. [Java 程序：查看 Armstrong 數字](https://beginnersbook.com/2017/09/java-program-to-check-armstrong-number/)