如何获得此循环以接受两个条目的正整数？

Question

为了更清楚，请通过menuChoice == 2帮助我。

我已经到了要输入负值的地步，它会提示您再次输入，直到它为正，然后计算就可以了。 但是，当我现在只输入正值时，它什么也不会计算。 我已经尝试了一段时间，但我无法弄清楚。

我需要做什么？

package finalExam;

//this is required for JOptionPane to work
import javax.swing.JOptionPane; 

public class Geometry {

    public static void main(String[] args) {


boolean valid = false;

int menuChoice;

do {
        // create a menu and display it to the user
        // then ask the user to choose an option
        String menu = "1) Calculate the area of a circle\n"
                    + "2) Calculate the area of a rectangle\n"
                    + "3) Calculate the area of a triangle\n"
                    + "4) Quit\n"
                    + "Please enter your choice: (1, 2, 3, or 4)";

        menuChoice = Integer.parseInt(JOptionPane.showInputDialog(menu));

        if(menuChoice == 1)
        {
            String unknownRadius = JOptionPane.showInputDialog("What is the radius of the circle?");
            if(Double.parseDouble(unknownRadius) < 0){
                do{
                JOptionPane.showMessageDialog(null, "Please enter positive numbers only.");
                unknownRadius = JOptionPane.showInputDialog("What is the radius of the circle?");
                }
                while(Double.parseDouble(unknownRadius) < 0);
                double knownRadius = Double.parseDouble(unknownRadius);
                double circleArea = Math.pow(knownRadius, 2) * 3.14159;
                JOptionPane.showMessageDialog(null, "The area of the circle is " + circleArea);
            }
            else if(Double.parseDouble(unknownRadius) > 0) {
            double knownRadius = Double.parseDouble(unknownRadius);
            double circleArea = Math.pow(knownRadius, 2) * 3.14159;
            JOptionPane.showMessageDialog(null, "The area of the circle is " + circleArea);
            valid = true;
            }

        } else if(menuChoice == 2){
            String unknownLength = JOptionPane.showInputDialog("What is the length of the rectangle?");
            if(Double.parseDouble(unknownLength) < 0){
                do{
                    JOptionPane.showMessageDialog(null, "Please enter positive numbers only.");
                    unknownLength = JOptionPane.showInputDialog("What is the length of the rectangle?");
                }
                while(Double.parseDouble(unknownLength) < 0);
                double knownLength = Double.parseDouble(unknownLength);
                String unknownWidth = JOptionPane.showInputDialog("What is the width of the rectangle?");
                if(Double.parseDouble(unknownWidth) < 0){
                    do{
                        JOptionPane.showMessageDialog(null, "Please enter positive numbers only.");
                        unknownWidth = JOptionPane.showInputDialog("What is the width of the rectangle?");
                    }
                    while(Double.parseDouble(unknownWidth) < 0);
                    double knownWidth = Double.parseDouble(unknownWidth);
                    double rectangleArea = knownLength * knownWidth;
                    JOptionPane.showMessageDialog(null, "The area of the rectangle is " + rectangleArea);
            }
            else if(Double.parseDouble(unknownLength) > 0){
            knownLength = Double.parseDouble(unknownLength);
            unknownWidth = JOptionPane.showInputDialog("What is the width of the rectangle?");
            if(Double.parseDouble(unknownWidth) > 0) {
                double knownWidth = Double.parseDouble(unknownWidth);
                double rectangleArea = knownLength * knownWidth;
                JOptionPane.showMessageDialog(null, "The area of the rectangle is " + rectangleArea);
                valid = true;
            }
            }
            }

        } else if(menuChoice == 3){
            String unknownBase = JOptionPane.showInputDialog("What is the base length of the triangle?");
            if(Double.parseDouble(unknownBase) > 0){
            double knownBase = Double.parseDouble(unknownBase);
            String unknownHeight = JOptionPane.showInputDialog("What is the height of the triangle?");
            if(Double.parseDouble(unknownHeight) > 0){
            double knownHeight = Double.parseDouble(unknownHeight);
            double triangleArea = (knownBase / 2) * knownHeight;
            JOptionPane.showMessageDialog(null, "The area of the triangle is " + triangleArea);
            valid = true;
            }
            else { JOptionPane.showMessageDialog(null, "Please enter a positive number");
                   JOptionPane.showInputDialog("What is the base length of the triangle?");
            }
            }
            else { JOptionPane.showMessageDialog(null, "Please enter a positive number");
                   JOptionPane.showInputDialog("What is the height of the triangle?");
            }

        }else if(menuChoice == 4){
            System.exit(0);

        } else
            JOptionPane.showMessageDialog(null, "Please select from the options given (1-4)!");
}

while(!valid || menuChoice != 4);

}
}

Answer 1

在第48行，您的语句if(Double.parseDouble(unknownLength) < 0){具有匹配的if(Double.parseDouble(unknownLength) < 0){括号在第76行，就在} else if(menuChoice == 3){ 。

因此，从逻辑menuChoice == 2当输入负数时，您的代码仅运行menuChoice == 2部分。 相反，您应该在第一个do-while循环完成后关闭if，因为此时该数字已被（校正为）正数。

您还应该尝试格式化代码。 它将使它更具可读性，并且在使用美化工具（例如Tutorial Point Online Java Formatter）之后，您可以轻松地看到花括号没有对齐在应有的位置。

Answer 2

根据第一个长度是负数还是正数，使用两个不同的代码块，对您来说，事情变得太复杂了。 基本上，您的代码如下所示：

If the length is negative then {
    Ask for a new length until it's positive
    Now input the width, reject negative values, do the computation,
    and output it
} else { // the length is positive
    Input the width, reject negative values, do the computation,
    and output it
}

有关处理宽度的整个部分在代码中发生了两次，这使代码不必要地变得复杂，并使其更容易出错，例如将花括号放在错误的位置（我认为这是代码不起作用的原因） 。 通过重新组织如下代码，您可以使自己的生活简单得多：

If the length is negative then {
    Ask for a new length until it's positive
}
// When we get here, the length will be positive.  It doesn't matter 
// whether we got here because the original length was positive, or whether
// it was negative and the user entered a new value.  We're going to 
// continue in the same way, either way.
Input the width, reject negative values, do the computation,
and output it

（顺便说一句，如果用户输入0，我不知道要做什么。您确实没有处理这种情况。）

Answer 3

据我了解，如果我只想实现您在问题中的要求，我可以简单地做到。

（我在JAVA中仅提供了备用代码，您可以相应地修改Japplet ）

int a=-1,b=-1;
a=sc.nextInt();
b=sc.nextInt();

if(a>=0 && b>=0){
  ...
  //do the task
}

else{
   while(a<0 || b<0){

      System.out.println("negative value not allowed, enter +ve value ");
      a=sc.nextInt();
      b=sc.nextInt();
   }

  // while exited only if value both a and b are positive
  //+ve value
  //perform task       
}