奇怪的「如果！=」Java錯誤

Question

我正在製作一個打印出來的程序，如果一個數字是素數，而它之前的素數，我有一個問題。我有：

if(i != 2){ System.out.println(primes[i] + ", "); else System.out.println(primes[i] +  "."); 

如果數字是2，它應該顯示「2」。但相反，它將任何數字以3結尾的期間，什麼是錯的？ ：P 這裏是我的代碼

package me.Jesse.PrimeCalc; 

import java.util.Scanner; 

public class PrimeArrayCalculator { 

public static void main(String[] args){ 
    Scanner scan = new Scanner(System.in); 
    int primeCounter = 0; 
    int arrayCounter = 0; 
    int[] primes; 
    int input; 

    System.out.println("Please Enter A Number."); 
    input = scan.nextInt(); 
    System.out.println("Calculating Results... (This may take a while!) "); 
    System.out.println(""); 
    if(isPrimeMethod.isPrime(input) == true){ 
     System.out.println(input + " Is Prime!"); 
     System.out.println("Calculating The Prime Numbers Before " + input + "..."); 
     System.out.println(""); 
    }else{ 
     System.out.println(input + " Is Not Prime."); 
     System.out.println("Calculating The Prime Numbers Before " + input + "..."); 
     System.out.println(""); 

    } 



    for (int i = input; i <= input; i--){ 
     if(isPrimeMethod.isPrime(i) == true){ 
      primeCounter++; 
     } 
    } 

    primes = new int[primeCounter++]; 

    for (int i = input; i <= input; i--){ 
     if(isPrimeMethod.isPrime(i) == true){ 
      primes[arrayCounter] = i; 
      arrayCounter++; 
     } 

    } 
    System.out.println("Here Are All The Prime Numbers Before " + input + ":"); 
    System.out.println(""); 
    for (int i = 0; i <= primeCounter; i++){ 
     try{ 
      if (primeCounter != 2) 
       System.out.println(primes[i] + ","); 
       else 
       System.out.println(primes[i] + "."); 
     }catch(ArrayIndexOutOfBoundsException e){ 
     // Yes I know the program trys to print from two invalid array index's. Try/Catch FTW. 
     } 

    } 
} 
    } 

Answer 1

我不知道是什麼問題你問，但這個應該怎麼辦呢？

for (int i = input; i <= input; i--){ 
     if(isPrimeMethod.isPrime(i) == true){ 
      primeCounter++; 
     } 
    } 

是什麼讓這個循環永遠停止？

Answer 2

好吧，有很多可以簡化的代碼，但這不是問題。

在這種情況下，i是數組的索引，而不是質數的實際值。相反，您應該檢查：

if(primes[i] != 2) 
    System.out.println(primes[i] + ", "); 
else 
    System.out.println(primes[i] + ".");