为什么我的代码在 else 语句后出现编译错误？答案

【问题标题】：Why does my code have a compilation error after the else statement?为什么我的代码在 else 语句后出现编译错误？
【发布时间】：2019-02-09 17:39:48
【问题描述】：

忍受我。

创建 if-else 语句后，每次我检查 else 语句时，如果字符串不正确，它是否可以返回菜单，它总是以错误结束，例如：线程“main”中的异常java.lang.NumberFormatException：对于输入字符串：“”

public class geo {
public static void main(String[] args){
byte choice = 0;
int num1 = 0;
int num2 = 0;
int num3  = 0;
float num4 ;
double result1 = 0;
boolean quit;
String UnitofMeasurement;
String feet = "feet";
String inches = "inches";
DecimalFormat format = new DecimalFormat("0.00");
Scanner key = new Scanner(System.in);
while (choice != 1) {
System.out.println("\t1. Determine the perimeter of a square");
switch (choice){
  case 1:
  System.out.println("The perimeter of a square is computed 
  by multiplying the measure of one side by 4.");
            System.out.println("Enter the unit of measurement(i.e. inches/feet):");
            UnitofMeasurement = key.next();// gets the unit of measurement
            if(UnitofMeasurement.equals(feet)||UnitofMeasurement.equals(inches)){
            System.out.println("You have chosen " + UnitofMeasurement + " as the unit of measurement.");
            System.out.println("Enter the measurement of one side: ");
            num1 = key.nextInt();
            System.out.println("Side of the square: "+ format.format(num1));
            key.nextLine();
            result1 = num1 * 4;
            System.out.println("Perimeter of the square = "+ format.format(result1) +" "+  UnitofMeasurement);
            }
            else
                {
                    System.out.println("Please only enter feet/inches");

                }
            enter();
            break;

默认；

【问题讨论】：

异常消息不是编译错误。另外，这个异常发生在哪一行？
java.lang.NumberFormatException: For input string: "" 告诉你，你试图将字符串转换为数字，而字符串是""，所以当然不能转换为数字。
@rgettman 它发生在 else 语句之后

标签： java if-statement

【解决方案1】：

如果这是您编写的所有代码，则编译错误在enter(); 和default; 中

我认为你必须在你的类中实现enter()方法，并将最后一个错误更改为default:

请看下面这段代码，没有编译错误：

public class geo {
    public static void main(String[] args) {
        byte choice = 0;
        int num1 = 0;
        int num2 = 0;
        int num3 = 0;
        float num4;
        double result1 = 0;
        boolean quit;
        String UnitofMeasurement;
        String feet = "feet";
        String inches = "inches";
        DecimalFormat format = new DecimalFormat("0.00");
        Scanner key = new Scanner(System.in);
        while (choice != 1) {
            System.out.println("\t1. Determine the perimeter of a square");
            switch (choice) {
            case 1:
                System.out.println("The perimeter of a square is computed by multiplying the measure of one side by 4.");
                System.out.println("Enter the unit of measurement(i.e. inches/feet):");
                UnitofMeasurement = key.next();// gets the unit of measurement
                if (UnitofMeasurement.equals(feet) || UnitofMeasurement.equals(inches)) {
                    System.out.println("You have chosen " + UnitofMeasurement + " as the unit of measurement.");
                    System.out.println("Enter the measurement of one side: ");
                    num1 = key.nextInt();
                    System.out.println("Side of the square: " + format.format(num1));
                    key.nextLine();
                    result1 = num1 * 4;
                    System.out.println("Perimeter of the square = " + format.format(result1) + " " + UnitofMeasurement);
                } else {
                    System.out.println("Please only enter feet/inches");

                }
                break;
            default:
            }
        }
    }
}

【讨论】：