如何創建只有偶數的數組副本？

Question

我必須創建一個方法，通過創建一個新數組來複制和打印數組中的偶數。我已經創建了一個名爲myNumbers的數組。我認爲問題在於myEvenNumbers[z]不會在myEvenNumbers[0]處存儲偶數，而是它會存儲第一個偶數在第一個索引myNumbers處的任何值。任何幫助將非常感激！

這是我的代碼到目前爲止。

public static void copyAndPrintEvenNumbers() { 
    System.out.println("All the even numbers are: "); 
    int count = 0; 

    for (int i =0; i < myNumbers.length; i++) { 
     if (myNumbers[i] % 2 == 0) { 
      count++; 
     } 
     int[] myEvenNumbers = new int[count]; 
     for (int z = 0; z < myNumbers.length; z++) { 
      if (myNumbers[z] % 2 ==0) { 
       myEvenNumbers[z] = myNumbers[z]; 
       System.out.println(myEvenNumbers[z]); 
      } 
     } 

    } 

} 

Answer 1

您必須爲myEvenNumbers數組聲明第二個索引。當z超過myEvenNumbers數組的元素總數時，您將得到一個IndexOutOfBounds。還像Connor說的那樣，這兩個循環不應該嵌套。否則，您將丟棄前面的數組實例（myEvenNumbers）並導致內存泄漏。

public static void copyAndPrintEvenNumbers() { 

    System.out.println("All the even numbers are: "); 
    int count = 0; 

    for (int i =0; i < myNumbers.length; i++) { 
     if (myNumbers[i] % 2 == 0) { 
      count++; 
     } 
    } 

    int[] myEvenNumbers = new int[count]; 
    int myEvenIndex = 0; 
    for (int z = 0; z < myNumbers.length; z++) { 
     if (myNumbers[z] % 2 ==0) { 
      myEvenNumbers[myEvenIndex] = myNumbers[z]; 
      System.out.println(myEvenNumbers[myEvenIndex]); 
      myEvenIndex++; 
     } 
    } 

} 

---

個人而言，我會選擇偶數陣列相同的大小（內存小的開銷），以消除在第一循環中，因爲偶數的數量不能超過原始數組的計數。

public static void copyAndPrintEvenNumbers() { 

    System.out.println("All the even numbers are: "); 
    int count = 0; 

    int[] myEvenNumbers = new int[myNumbers.length]; 
    int count = 0; 
    for (int z = 0; z < myNumbers.length; z++) { 
     if (myNumbers[z] % 2 ==0) { 
      myEvenNumbers[count] = myNumbers[z]; 
      System.out.println(myEvenNumbers[count]); 
      count++; 
     } 
    } 
    System.out.println("There are " + count + " even numbers found"); 
} 

Answer 2

沒有必要讓你的第二個循環在第一個循環內。試試這個：

public static void copyAndPrintEvenNumbers() { 
    System.out.println("All the even numbers are: "); 
    int count = 0; 

    for (int i =0; i < myNumbers.length; i++) { 
     if (myNumbers[i] % 2 == 0) { 
      count++; 
     } 
    } 

    int[] myEvenNumbers = new int[count]; 
    int index = 0; 
    for(int i = 0; i < myNumbers.length; i++) { 
     if (myNumbers[i] % 2 ==0) { 
      myEvenNumbers[index] = myNumbers[i]; 
      index++; 
     } 
    } 
    System.out.println(myEvenNumbers); 
}