Question

我正在试图弄清楚为什么Code的顶部块会执行但底部的代码块却没有。我所做的就是让对方执行是在if / else语句中切换条件位置

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

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);
            }
    }

您的递归调用不会发生，因为在开始时瓶子是0.尝试移动递归调用的位置或将elseif更改为if。

Answer 2

问题与递归无关，但事实上＆＃34; if＆＃34;和＃34;其他＆＃34;不是相互排斥的。您只能安全地切换＆＃34;的顺序，如果＆＃34;和＃34;其他＆＃34;如果条件是独家的。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 3

您切换条件if (bottles <= 99)和else if (bottles == 0)会导致第一个块执行，因为瓶子= 0时第一个条件（瓶子<= 99）为真。

如果您希望else if在if语句之前执行，那么这种情况永远不会发生。

也许你的情况应该是类似if (bottles > 0 && bottles <= 99)的情况，在这种情况下，如果瓶子= 0，你的第二个区块将会执行。

Answer 4

在第二种方法中，分支bottles == 0将永远不会执行。

因为bottles == 0时bottles <= 99为真。它是一个无限的递归循环。

If / Else语句中的Java递归

4 个答案: