需要一个不满足的 if 语句来转到代码开头

Question

我正在尝试设置一些 if 语句，以确保用户输入不会超出我设置的范围（如果我希望 if 语句将它们返回到主代码的开头）。String animal = JOptionPane.showInputDialog("Enter In Animal Name"); // Asking for user to enter a animalString fruit = JOptionPane.showInputDialog("Enter In A Fruit Name"); // Asking user to enter a fruitint days = Integer.parseInt(JOptionPane.showInputDialog("Enter In How Many Days Between 1 And 10"));// Above integer is asking the user to enter the amount of days.// Below if statements are basically error checking to ensure the user stays between the// range asked for when they are asked to enter in days between 1 and 10.if (days <= 0) { // Ensures that negative numbers cannot be entered.    JOptionPane.showMessageDialog(null, "Error, Please enter a number between 1 and 10");    return;}if (days >= 10) { // Ensures nothing over 10 can be entered.    JOptionPane.showMessageDialog(null, "Error, Please enter a number between 1 and 10");    return;}如果 if 语句说它是一个错误，它应该返回要求他们重新输入天数

Answer 1

使用do-while至少执行一次的循环，如果days不满足条件则每次都循环回来。

public static void main(String[] args) 

{

    do {

        //Your other code

        String animal = JOptionPane.showInputDialog("Enter In Animal Name"); // Asking for user to enter a animal

        String fruit = JOptionPane.showInputDialog("Enter In A Fruit Name"); // Asking user to enter a fruit

        int days = askForInput();

        if (days <= 0 || days >= 10) { // Ensures that negative numbers cannot be entered.

            JOptionPane.showMessageDialog(null, "Error, Please enter a number between 1 and 10");

        }

    } while (days <= 0 || days >= 10);

}

//Pass whatever parameters you might need

public static int askForInput() {

    int days = Integer.parseInt(JOptionPane.showInputDialog("Enter In How Many Days Between 1 And 10"));

    //Any other code you want

    return days;

}

我还将它提取到一个方法中，这可能是不必要的，但如果需要，它可以让您添加更多功能。

如果您不想每次都被问到这个问题，您也可以移动animal或fruit离开。do

Answer 2

允许代码重新启动代码块（即返回到开头并重试）的一种方法是使用带有“永远”循环的continueand语句。break

for (;;) { // loop forever

    // some code here

    if (failure condition 1) {

        // handle failure here

        continue; // go back and try again

    }

    if (failure condition 2) {

        // handle failure here

        continue; // go back and try again

    }

    // more code and failure condition checks here

    break; // unconditional exit loop, since all is ok

}

如果“此处的某些代码”本身位于循环内，但需要返回到开头并重试，则可以为此使用标签：

TRYAGAIN: for (;;) { // loop forever

    // some code here

    for (some looping here) {

        // some code here

        try {

            if (failure condition) {

                // handle failure here

                continue TRYAGAIN; // go back and try again

            }

        } finally {

            // code here will execute, even if 'continue' is used

        }

    }

    // more code and failure condition checks here

    break; // unconditional exit loop, since all is ok

}

Answer 3

String animal;

String fruit;

int days = 0;

animal = JOptionPane.showInputDialog("Enter In Animal Name");

fruit = JOptionPane.showInputDialog("Enter In A Fruit Name");

while(days <= 0 || days > 10) {

    days = Integer.parseInt(JOptionPane.showInputDialog("Enter In How Many Days Between 1 And 10"));

    if (days <= 0 || days > 10) {

        JOptionPane.showMessageDialog(null, "Error, Please enter a number between 1 and 10");

    }

}

Answer 4

使用 while 循环

// Your user prompt for animal and fruit goes here

boolean exit = false;

while(!exit)

{

    // Your user prompt for days code goes here

    if (days <= 0 || days > 10) {

        JOptionPane.showMessageDialog(null, "Error, Please enter a number between 1 and 10");

        exit = false; // This is not necessary but nice for readability's sake

    }

    else {

        exit = true;

    }

}