Java在If/Else语句中的递归

Question

我想知道为什么代码的顶层代码执行但代码的底部代码块没有。我所做的一切让对方执行了切换在我的if/else语句的条件位置

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

你的切换条件if (bottles <= 99)和else if (bottles == 0)使第一块来执行，因为第一条件（瓶< = 99）是用于瓶子= 0真。

如果您希望在if声明之前执行else if，那么这绝不会发生。

也许你的情况应该是if (bottles > 0 && bottles <= 99)，在这种情况下，如果瓶子= 0，你的第二个区块将按照你的预期执行。

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); 
      } 
    } 

你的递归调用不会发生，因为在开始的瓶子为0尝试移动的位置，你的递归调用或将elseif更改为if。

Answer 3

该问题与递归无关，但事实上“if”和“else”中的条件并不相互排斥。 只有只有安全地切换“if”和“else”的顺序，如果条件是排他性的。请记住，在if/elseif链中，只会执行第一个匹配条件。如果条件不相互排斥，则订单将很重要。

Answer 4

在第二种方法中，分支bottles == 0将永远不会执行。

因为当bottles == 0，bottles <= 99为真。这是一个无限的递归循环。