私有函數應該如何進行參數驗證或用戶輸入以及內部數據結構？

Question

下面的代碼將返回總和爲x的整數對，例如：if arr {1,2,3,4,5]並且x是7，那麼list應該包含{3,4}和{2,5} 。主要目標是瞭解如何以私有方法執行參數驗證。問題嵌套在評論中，請僅對提出的問題提出建議。感謝您在代碼中檢查我的問題。

public static List<Pair> getPairsFromPositiveArray(int[] arr, int x) { 
    // check for all positive integers 
    for (int i : arr) { // if arr is null, then this loop would throw NPE. So no need to make an exclicit check for null. 
     if (i < 0) throw new IllegalArgumentException("No integer should be negative."); 
    } 
    final List<Pair> list = new ArrayList<Pair>(); 
    getPair(arr, x, list); 
    return list; 
} 

private static void getPair(int[] arr, int x, List<Pair> list) { 
    // QUESTION 1: Should check of "all positive integers" be done here too ? 

    /* 
    * QUESTION 2: 
    * list is data structure which we created internally (user did not provide it) 
    * Does anyone suggest, it throw an NPE or do an explicit assert check for list != null ? 
    */ 
    assert list != null; // form my understanding of e effective java. 
    assert arr != null; // form my understanding of e effective java. 

    final Set<Integer> set = new HashSet<Integer>(); 
    /* 
    * QUESTION 3: 
    * arr is a data structure which was input by the user. 
    * Should we check for assert arr != null or let loop throw a NPE ? 
    */ 
    for (int i : arr) { 
     if (set.contains(i)) { 
      System.out.println(i + " : "); 
      list.add(new Pair(i, x - i)); 
     } else { 
      set.add(x - i); 
     } 
    } 
} 

Answer 1

問題1：我會在for()循環中執行它，否則您必須循環兩次。但是......你的電話程序在這種情況下期待什麼？

問題2：如果列表是null爲什麼不初始化呢？如果arr是null，那麼是的有一個問題。在這種情況下你又會期待什麼？

問題3：您檢查arr == null每個問題。

通常良好的編程是防禦性編程。始終假定提供了錯誤或錯誤的輸入。另一方面，對於一個合理簡單的方法，你不需要過於複雜的事情。

Answer 2

問題1：在這裏也應該檢查「所有正整數」嗎？

Ans：Nope;因爲你將調用getPairsFromPositiveArray()getPair()之前獲取列表

問題2： *名單是我們內部創建（用戶沒有提供它）
*有誰表明，它拋出一個NPE數據結構或做一個明確的斷言檢查列表！= null？

答案：斷言

問題3： * ARR是一種數據結構，其是由用戶輸入。 *我們應該檢查斷言ARR = null或讓環拋出NPE

答：！

• ，一定要進行全面的檢查....所以，是的，做檢查的ARR = NULL

• 總是喜歡斷言對拋NPE

Answer 3

的答案是真的直線前進，

public static List<Pair> getPairsFromPositiveArray(int[] arr, int x) 
{  
    // if arr is null, then this loop would throw NPE. So no need to make an explicit check for null. 

    //  for (int i : arr) //No need we can check downward 
    //  { 
    //  } 
    final List<Pair> list = new ArrayList<Pair>(); 
    getPair(arr, x, list); 
    return list; 
} 

private static void getPair(int[] arr, int x, List<Pair> list) throws NullPointerException //TELLS THIS WILL THROW NPE 
{ 
    // QUESTION 1: Should check of "all positive integers" be done here too ? 

    /* 
    * QUESTION 2: 
    * list is data structure which we created internally (user did not provide it) 
    * Does anyone suggest, it throw an NPE or do an explicit assert check for list != null ? 
    */ 
    //NO CHECK ARE REQUIRED HERE AS List<Pair> list IS NULL THEN IF WE REASSIGN IT ALSO THEN IT WILL NOT BE REFLECTED BACK TO ORIGINAL, YOU CAN THROW A CUSTOM EXCPETION OR NPE AND DOCUMENT IT (ADD TO METHOD THROWS NPE) 


    final Set<Integer> set = new HashSet<Integer>(); 
    /* 
    * QUESTION 3: 
    * arr is a data structure which was input by the user. 
    * Should we check for assert arr != null or let loop throw a NPE ? 
    //NO CHECK ARE REQUIRED HERE AS int[] arr IS NULL THEN IF WE REASSIGN IT ALSO THEN IT WILL NOT BE REFLECTED BACK TO ORIGINAL, YOU CAN THROW A CUSTOM EXCPETION OR NPE AND DOCUMENT IT (ADD TO METHOD THROWS NPE) 
    */ 
    for (int i : arr) 
    { 
     if (i < 0) // ANSWER TO QUESTION 1 
      throw new IllegalArgumentException("No integer should be negative."); 

     if (set.contains(i)) 
     { 
      System.out.println(i + " : "); 
      list.add(new Pair(i, x - i)); 
     } 
     else 
     { 
      set.add(x - i); 
     } 
    } 
}