Java在If/Else語句中的遞歸

Question

我想知道爲什麼代碼的頂層代碼執行但代碼的底部代碼塊沒有。我所做的一切讓對方執行了切換在我的if/else語句的條件位置

public static void onTheWall(int bottles){ 
    if (bottles == 0){ 
     System.out.println("No bottles of beer on the wall," 
          + " no bottles of beer, ya’ can’t take one down, ya’ can’t pass it around," 
          + "cause there are no more bottles of beer on the wall!"); 
    } else if (bottles <= 99){ 
     System.out.println(bottles + " bottles of beer on the wall, " 
          + bottles + " bottles of beer, ya’ take one" 
          + " down, ya’ pass it around, " 
          + (bottles - 1) + " bottles of beer on the wall"); 
     onTheWall(bottles-1); 
    } 
} 

public static void onTheWall(int bottles){ 
    if (bottles <= 99){ 
     System.out.println(bottles + " bottles of beer on the wall, " 
          + bottles + " bottles of beer, ya’ take one" 
          + " down, ya’ pass it around, " + (bottles - 1) 
          + " bottles of beer on the wall"); 
     onTheWall(bottles-1); 
    } else if (bottles == 0){ 
     System.out.println("No bottles of beer on the wall," 
          + " no bottles of beer, ya’ can’t take one down, ya’ can’t pass it around," 
          + "cause there are no more bottles of beer on the wall!"); 
    } 
} 

Answer 1

你的切換條件if (bottles <= 99)和else if (bottles == 0)使第一塊來執行，因爲第一條件（瓶< = 99）是用於瓶子= 0真。

如果您希望在if聲明之前執行else if，那麼這絕不會發生。

也許你的情況應該是if (bottles > 0 && bottles <= 99)，在這種情況下，如果瓶子= 0，你的第二個區塊將按照你的預期執行。

Answer 2

public static void onTheWall(int bottles){ 
     if (bottles == 0){ 
       System.out.println("No bottles of beer on the wall," + " no bottles of beer, ya’ can’t take one down, ya’ can’t pass it around," + "cause there are no more bottles of beer on the wall!"); 
      } else if (bottles <= 99){ 
       System.out.println(bottles + " bottles of beer on the wall, " + bottles + " bottles of beer, ya’ take one" 
       + " down, ya’ pass it around, " + (bottles - 1) + " bottles of beer on the wall"); 
      onTheWall(bottles-1); 
      } 
    } 

你的遞歸調用不會發生，因爲在開始的瓶子爲0嘗試移動的位置，你的遞歸調用或將elseif更改爲if。

Answer 3

該問題與遞歸無關，但事實上「if」和「else」中的條件並不相互排斥。 只有只有安全地切換「if」和「else」的順序，如果條件是排他性的。請記住，在if/elseif鏈中，只會執行第一個匹配條件。如果條件不相互排斥，則訂單將很重要。

Answer 4

在第二種方法中，分支bottles == 0將永遠不會執行。

因爲當bottles == 0，bottles <= 99爲真。這是一個無限的遞歸循環。