if-else 不应该有 break 吗？

Question

所以我的教授提到 if/if-else 语句中的中断是 "bad" 代码。她到底是什么意思？另外，我怎样才能修复我目前编写的代码，因为它确实按照我想要的方式工作，现在我需要摆脱 break 语句。

    int sumOne = 1;
    int sumTwo = 1;
    int sumOneTotal = 0;
    int sumTwoTotal = 0;
    while(sumOne > 0 || sumTwo > 0){
        System.out.print("Enter a number to add to first sum: ");
        //The user enters in a value for the first sum.
        sumOne = input.nextInt();

        /**
         * We use an if-else statment to ensure sumOne is never less than or equal to 0.
         * If it does it ends the program immediately and totals the sums.
         * This is because we only want the user to enter in positive numbers.
         */
        if (sumOne <= 0){
            break;
        }else{
            sumOneTotal = sumOneTotal + sumOne;
        }

        System.out.print("Enter a number to add to second sum: ");
        //The user enters in a value for the second sum.
        sumTwo = input.nextInt();

        /**
         * We use an if-else statment to ensure sumTwo is never less than or equal to 0. 
         * If it does it ends the program immediately and totals the sums.
         * This is because we only want the user to enter in positive numbers.
         */
        if (sumTwo <= 0){
            break;
        }else{
            sumTwoTotal = sumTwoTotal + sumTwo;
        }
    }
    //We print out the total of sumOneTotal and sumTwoTotal.
    System.out.printf("%1s%1d%12s%1s%1d", "First sum: ", sumOneTotal, " ", "Second sum: ", sumTwoTotal);

本质上，我希望用户输入任何正数，然后将该数字添加到第一个或第二个总和中。一旦用户输入任何数字 <= 0 我希望程序立即停止。当我修改代码时，我一直遇到的问题是代码保持运行通过。这意味着如果我让用户输入 0 以添加到第一个总和中，代码仍然要求用户为第二个总和输入一个数字。我需要它立即停止而不是继续。任何帮助都会有很大的帮助！我正在使用 Java.

编辑！！！所以假设我想制作一个程序来做我现在正在做的完全相同的事情，只是没有 break 语句。我该怎么做？一些规则。最外面的语句必须是 "while" 循环。它的内部运作可以是任何东西。我还需要机器交替打印出 "Enter a number to add to first sum:" 和 "Enter a number to add to second sum:"。因此，如果我输入 1、2、3、4。第一个和是 4，第二个和是 6。最后的规则是它不能包含任何 break 语句！

Answer 1

有时候避免中断比使用它更糟糕。我会这样写，少一个休息。

int sumOneTotal = 0;
int sumTwoTotal = 0;
while (true) {
    System.out.print("Enter a number to add to first sum: ");
    //The user enters in a value for the first sum.
    int sumOne = input.nextInt();

    if (sumOne <= 0) 
        break;

    sumOneTotal += sumOne;

    System.out.print("Enter a number to add to second sum: ");
    //The user enters in a value for the second sum.
    int sumTwo = input.nextInt();

    if (sumTwo <= 0)
        break;
    sumTwoTotal += sumTwo;
}

您可以避免中断，但这不会生成代码 clearer/simpler 恕我直言。

int sumOneTotal = 0;
int sumTwoTotal = 0;
boolean okay = true;
do {
    System.out.print("Enter a number to add to first sum: ");
    //The user enters in a value for the first sum.
    int sumOne = input.nextInt();

    if (sumOne <= 0) {
        okay = false;
    } else {
        sumOneTotal += sumOne;

        System.out.print("Enter a number to add to second sum: ");
        //The user enters in a value for the second sum.
        int sumTwo = input.nextInt();

        if (sumTwo <= 0) {
            okay = false;
        } else {
            sumTwoTotal += sumTwo;
        }
} while (okay);

同样的建议也适用于使用标签。尽可能避免它们，除非避免它们意味着做更糟糕的事情。

Answer 2

我不一定同意在 if 中使用 break 总是不好的做法。然而，这更多的是见仁见智，并不是真正的主题。我将回答您问题中与主题相关的部分，即：如何修复我的代码以不在 if.

中使用 break

下面的代码将继续循环，要求用户输入，直到他们输入有效数字。这避免了您原来的问题，并且有一个额外的好处，即允许用户在犯错时有机会输入新数字，而不是退出循环并重新开始。

int sumOne = 1;
int sumTwo = 1;
int sumOneTotal = 0;
int sumTwoTotal = 0;
while(sumOne > 0 || sumTwo > 0){
    do {
        System.out.print("Enter a number to add to first sum: ");
        //The user enters in a value for the first sum.
        sumOne = input.nextInt();

        System.out.print("Enter a number to add to second sum: ");
        //The user enters in a value for the second sum.
        sumTwo = input.nextInt();
    }while(sumTwo <= 0 || sumOne <= 0);

    sumOneTotal = sumOneTotal + sumOne;
    sumTwoTotal = sumTwoTotal + sumTwo;
}
//We print out the total of sumOneTotal and sumTwoTotal.
System.out.printf("%1s%1d%12s%1s%1d", "First sum: ", sumOneTotal, " ", "Second sum: ", sumTwoTotal);

Answer 3

这是对结构化编程还是新事物的倒退，回到 goto 语句等无处不在的时代。理论上，理想情况下，应该永远不用breaks/continues，只有return的单点。实际上，这样做可以通过使程序更难编写、更难阅读并占用更多计算资源，从而使您的工作变得更加困难。多个 returns、continues 和 breaks 是真正结构化编程和意大利面条代码之间的中间人。使用得当，没毛病。

一般来说，我发现如果您已经在使用使代码难以阅读的不良做法（例如，编写大量逻辑块而不分解它，紧密耦合对象），它们只会使您的代码模糊不清等）。

如果您有兴趣，here is a link to an interesting perspective on why NOT to use them. And here 是关于它们为何有益的观点。

许多其他人已经用代码回答了，但这是我的镜头:)

public class Main {
    public static void main(String args[]) {
        int sumOne = 1;
        int sumTwo = 1;
        int sumOneTotal = 0;
        int sumTwoTotal = 0;
        Scanner input = new Scanner(System.in);
        while(sumOne > 0 || sumTwo > 0){
            System.out.print("Enter a number to add to first sum: ");
            sumOne = input.nextInt();
            if (is_positive(sumOne)){
                sumOneTotal = sum_numbers(sumOneTotal, sumOne);
                System.out.print("Enter a number to add to second sum: ");
                sumTwo = input.nextInt();
                if(is_positive(sumTwo)){
                    sumTwoTotal = sum_numbers(sumTwoTotal, sumTwo);
                }
            }
        }
        System.out.printf("%1s%1d%12s%1s%1d", "First sum: ", sumOneTotal, " ", "Second sum: ", sumTwoTotal);
        return;
    }
    public static int sum_numbers(int x, int y){
        int total = x + y;
        return total;
    }
    public static boolean is_positive(int x){
        boolean is_pos = true;
        if(x < 0){
            is_pos = false;
        }
        return is_pos;
    }
}

我会说它现在更难阅读了。我的代码越靠右，我就越为需要维护它的人感到难过。当然，我可以通过在方法中包装（更多）位来删除一两个级别的缩进。然后它变得更容易阅读，但有一点黑盒化每一点逻辑似乎都是多余的......

Answer 4

    while (sumOne > 0 && sumTwo > 0) {
        System.out.print("Enter a number to add to first sum: ");
        sumOne = input.nextInt();
        if (sumOne > 0) {
            sumOneTotal = sumOneTotal + sumOne;
            System.out.print("Enter a number to add to second sum: ");
            sumTwo = input.nextInt();
            if (sumTwo > 0)
                sumTwoTotal = sumTwoTotal + sumTwo;
        }
    }

但我同意其他人的看法 - 没有任何意义可以避免 "break"

Answer 5

更干净，没有中断。

int candidate  = 0;
int [] sums = {0,0};
int index = 1;

System.out.print("Enter a number to add to first sum: ");

while((candidate = input.nextInt()) > 0){
    sums[index] = sums[index] + candidate;
    index = (index + 1)%2;

    System.out.print("Enter a number to add to " + ((index == 0) ? "first":"second" ) + " sum: ");
    }
//We print out the totals.
System.out.printf("%1s%1d%12s%1s%1d", "First sum: ", sums[0], " ", "Second sum: ", sums[1]);

这并不是说您应该始终避免中断，但在这种情况下您可以避免中断以使您的代码更短、冗余更少。

Answer 6

如果你把你的代码流程图画出来你可以看到它中间有一个bucle退出，这是不对的，正确的方法是在评估时退出，也有人在评估时退出阅读您的代码，他们应该期望在 while 块内评估为 false 而不是随机的时，bucle 会留下，我获取了您的代码并进行了一些修复以使其按预期工作，但我不确定这是否是您的原因老师期待

    int sumOne = 1;
    int sumTwo = 1;
    int sumOneTotal = 0;
    int sumTwoTotal = 0;
    while (sumOne > 0 && sumTwo > 0) {
        System.out.print("Enter a number to add to first sum: ");
        // The user enters in a value for the first sum.
        sumOne = input.nextInt();

        /**
         * We use an if-else statment to ensure sumOne is never less than or
         * equal to 0. If it does it ends the program immediately and totals
         * the sums. This is because we only want the user to enter in
         * positive numbers.
         */
        if (sumOne > 0) {
            sumOneTotal = sumOneTotal + sumOne;
            System.out.print("Enter a number to add to second sum: ");
            // The user enters in a value for the second sum.
            sumTwo = input.nextInt();

            /**
             * We use an if-else statment to ensure sumTwo is never less
             * than or equal to 0. If it does it ends the program
             * immediately and totals the sums. This is because we only want
             * the user to enter in positive numbers.
             */
            if (sumTwo > 0) {
                sumTwoTotal = sumTwoTotal + sumTwo;
            }
        }
    }

if-else 不应该有 break 吗？

If-else should not have break?

java

break

while-loop