java - 一维数组不在 for 循环中打印，始终等于 0

Question

我正在制作一个二十一点程序。在 cardDraw 方法中，我在返回之前的末尾有一个 for 循环，应该 println 每个数组值，但是当我运行程序时没有显示任何内容。此外，当我在 main 方法中打印数组时，即使我在方法中设置值，每个值都是 0。有人可以解释一下为什么会发生这些事情吗？这可能是一个逻辑错误，但我在程序中的其他方法中遇到了这个问题。我们只允许使用一维数组。提前致谢。

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public class blackjack {

    public static int [] drawCard(int [] cardValues, int [] otherUserCardValues) {

        int duplicates = 0;

        //fills array with cards    
        for (int count = 0; count == cardValues.length; count++) {

            duplicates = 0;
            cardValues [count] = (int)(Math.random() * 12) + 1;

            //Checks for duplicate cards in one of the hands
            for (int count2 = 0; count2 == cardValues.length; count2++) {

                if (cardValues [count] == cardValues [count2]) {
                    duplicates++;
                } //end of  if (cardValues [count] == cardValues [count2])

            } //end of  for (int count2 = 0; count != 7; count++)

            //Checks for duplicate cards in the other hand
            for (int count2 = 0; count2 == cardValues.length; count2++) {

                if (cardValues [count] == otherUserCardValues [count2]) {
                    duplicates++;
                } //end of  if (cardValues [count] == cardValues [count2])

            } //end of  for (int count2 = 0; count != 7; count++)

            //makes it loop again if there are duplicates
            if (duplicates > 4) {
                count--;
            } //end of  if (duplicates > 4)

        } //end of  for (int count = 0; count != 7; count++)

        for (int count = 0; count == cardValues.length; count++) {
            System.out.println(cardValues[count]);
        }


        return cardValues;

    } //end of  cardDraw


    public static void main(String[] args) {

        //user variables
        double money = 0;
        int userCardTotal = 0;
        int userCardCount = 0;

        int [] lowerUserCards = {0, 0, 0, 0, 0, 0};
        int [] higherUserCards = {0, 0, 0, 0, 0, 0};
        int [] userCardValues = {0, 0, 0, 0, 0, 0};
        String [] userCardNames = {"a", "a", "a", "a", "a", "a"};
        String [] userCardSuits = {"a", "a", "a", "a", "a", "a"};

        //dealer variables
        int dealerCardTotal = 0;
        int dealerCardCount = 0;

        int [] lowerDealerCards = {0, 0, 0, 0, 0, 0};
        int [] higherDealerCards = {0, 0, 0, 0, 0, 0};
        int [] dealerCardValues = {0, 0, 0, 0, 0, 0};
        String [] dealerCardNames = {"a", "a", "a", "a", "a", "a"};
        String [] dealerCardSuits = {"a", "a", "a", "a", "a", "a"};

///////////////////////////////////////////////////////////////////////

        //methods
        userCardValues = drawCard(userCardValues, dealerCardValues);
        dealerCardValues = drawCard(dealerCardValues, userCardValues);

    } //end of main

} //end of class

Answer 1

for 循环只是一个稍微修饰过的 while 循环。

循环:

for (initial; condition; increment) {
   // do something
}

相当于:

initial;
while(condition) {
    // do something

    increment;
}

有一点异常(exception)，初始语句中描述的变量仅具有循环范围。

当你写下:

for (int i = 0; i == array.length; i++) {
    doSomething(array[i]);
}

程序首先声明一个名为i的变量并将其设置为0。然后，它进入 while 循环，条件为:i == array.length，该循环立即返回 false，因此循环在完成第一次迭代之前退出。

迭代循环的标准语法是:

for (int i = 0; i < array.length; i++) {
    doSomething(array[i]);
}

(可以说)更易读的方法是使用“for-each”循环:

for (int value : array) {
    doSomething(value);  // loops over all values in the array, creating a variable value in each iteration
}

更好的是，使用 Java 8 函数样式/流:

Arrays.asList(array).forEach(blackjack::doSomething);

// or using streams
Arrays.stream(array).forEach(blackjack::doSomething);