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，直到输入正值，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);
}
}
最佳答案
根据第一个长度是负数还是正数，您需要两个不同的代码块，这使您自己变得太复杂了。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过程在代码中发生了两次，这使代码不必要地变得复杂，并使它更容易出错，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。）
关于java - 如何获得此循环以接受两个条目的正整数？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/40012786/