Java 为什么我的代码在else语句之后有编译错误？

请容忍我

创建if-else语句后，每次我检查else语句是否可以返回菜单，如果字符串不正确，它总是以错误结束，如：线程“main”java.lang.NumberFormatException:For input string:“

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违约

如果这是您编写的所有代码，那么编译错误都在

enter（）中和
默认值

我认为您必须在类中实现
enter（）
方法，并将最后一个错误更改为
default:

请参阅下面的代码，无编译错误：

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:
            }
        }
    }
}  

异常消息不是编译错误。另外，此异常发生在哪一行？
java.lang.NumberFormatException:对于输入字符串：“
告诉您试图将字符串转换为数字，而字符串是
”
，因此当然，它无法转换为数字。@rgetman它发生在else语句之后
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:
            }
        }
    }
}