更新：感谢有关保留代码 SSCCE 的建议。就像我说的，这是我第一次在这里发帖。下次我一定会花时间确保代码被充分精简，然后再在这里发布。
所以我正在为我的计算机科学课编写一个程序，并且遇到了一个我无法弄清楚的奇怪问题。我试图通过使用 try/catch 语句来阻止无效的数据类型输入，从而使我的程序变得健壮，以免它破坏并结束整个程序，但它似乎不起作用。当输入了无效的数据类型时，程序结束时不会在窗口中显示任何 Java 的标准错误消息。我不知道为什么会这样，但我认为我错误地使用了 try/catch 语句。这是我的程序的两个类：
/* The core class for the finance calculations to be done in the FinanceApp class. */
public class FinanceCore{
// Instance variables
int numYears;
double principal;
double interestRate;
double balance;
public FinanceCore(){
numYears = 0;
principal = 0;
interestRate = 0;
balance = 0;
}
// Mutator methods that return boolean values depending on whether the input was valid or not
public boolean setYears(int y){
if(y >= 0){
numYears = y;
return true;
}
else return false;
}
public boolean setPrincipal(double p){
if(p >= 0){
principal = p;
balance = principal;
return true;
}
else return false;
}
public boolean setInterestRate(double ir){
if(ir >= 0 && ir <= 1){
interestRate = ir;
return true;
}
else return false;
}
// Two accessors
public int getYears(){
return numYears;
}
public double getPrincipal(){
return principal;
}
// This method calculates and returns the balance at the end of each year
public double plusYear(){
balance = balance*(1+interestRate);
return balance;
}
}
/* This program recieves three pieces of data (interest rate, principal amount, number of years) and generates an output
* table that shows how much money will be in a fund with the given parameters at the end of every year. */
import java.util.Scanner;
public class FinanceApp{
public static void main(String[]args){
// First, we will declare our global variables, and set them to default values
Scanner reader = new Scanner(System.in);
FinanceCore account = new FinanceCore();
int menuItem = 0;
// Now, we'll greet the user (because we're friendly like that)
System.out.println("Welcome! Please select a menu option below.");
while(true){
/* Now, our first user interface: a menu system that displays four options to the user arranged in
* columns for aesthetic effect. This is accomplished using the printf method.
*/
System.out.printf("%n%-20s%-20s%n%-20s%-20s%n%-20s%n",
"Set Principal[1]","Set Interest Rate[2]","Set Timespan[3]","Calculate[4]","Quit[5]");
System.out.print(": ");
// Now we get the user input until it is valid, and catch and errors in input type
try {
menuItem = reader.nextInt();
}
catch(Exception e){
reader.nextLine(); // Clear the input stream to avoid an infinite loop
System.out.println("Please a valid number 1-5.");
}
// The code for setting the principal amount
if(menuItem == 1){
while(true){
System.out.print("Please enter the principal investment amount: ");
try{
if(account.setPrincipal(reader.nextDouble()));
break;
}
catch(Exception e){
reader.nextLine(); // Clear the input stream to avoid an infinite loop
System.out.println("Please enter a valid dollar amount.");
}
}
}
// The code for setting the interest rate
else if(menuItem == 2){
while(true){
System.out.print("Please enter the quarterly interest rate: ");
try{
if(account.setInterestRate(reader.nextDouble()));
break;
}
catch(Exception e){
reader.nextLine(); // Clear the input stream to avoid an infinite loop
System.out.println("Please enter a valid decimal number between 0 and 1 (inclusive).");
}
}
}
// The code for setting the number of years
else if(menuItem == 3){
while(true){
System.out.print("Please enter the number of years the account will exist: ");
try{
if(account.setYears(reader.nextInt()));
break;
}
catch(Exception e){
reader.nextLine(); // Clear the input stream to avoid an infinite loop
System.out.println("Please enter a valid integer value.");
}
}
}
// This part actually executes the calculation
else if(menuItem == 4){
System.out.printf("%-10s%-10s%n%-10d%-10.2f%n","YEAR","BALANCE",0,account.getPrincipal());
int count = 1;
for(int c = account.getYears(); c > 0; c--){
System.out.printf("%-10d%-10.2f%n",count,account.plusYear());
count++;
}
}
// If the user enters any other number, the program quits
else
break;
}
}
}
请注意，该程序存在一个我似乎无法修复的持久性问题。出于某种原因，每次用户在菜单选择提示符处输入无效的数据类型时，程序就会结束（尽管没有抛出任何错误）。