java.lang.NumberFormatException - 找不到错误所在

Question

我收到此消息:

Exception in thread "main" java.lang.NumberFormatException: null
    at java.lang.Integer.parseInt(Integer.java:454)
    at java.lang.Integer.parseInt(Integer.java:527)
    at fdc.programming.VendingMachine.InsertMoney(VendingMachine.java:70)
    at fdc.programming.VendingMachineDriver.main(VendingMachineDriver.java:30)
Java Result: 1

我一直在尝试解决如何进行验证循环，以便只接受正整数，但我暂时放弃了，但我没有更改任何内容，并将所有内容恢复为乱七八糟之前的样子。现在，当我尝试输入数字时，它会出现上述错误，但 Netbeans 中没有错误，我可以用它来找出问题所在!请注意，我在大学只完成了一个 Java 基本模块；)

我的代码是:

public class VendingMachine
{
String sinsertMoney, sinsertMoney2; // Money inserted value for parsing into int
String productName;     // Name of product

int insertMoney, insertMoney2;  // Money inserted by customer (int = pence)
int price;                  // Price of products on sale
int changeLeft;         // Change left from inserted money after selection

int again;          // variable for deciding program repeat

DecimalFormat pence = new DecimalFormat("#p");  // Format display output for pence

public void InsertMoney() {
    String soption;             // Variable for machine operation
    productName = " Nothing";
    insertMoney = 0;        // Default inserted money initialised to zero
    insertMoney2 = 0;   // Default additional inserted money initialised to zero
    price = 0;          // Initialising money variables

    // Vending machine welcome dialog

    soption = JOptionPane.showInputDialog(
            "============================================"
            + "\nWelcome to the College Vending Machine!" 
            + "\n============================================"
            + "\n\nOptions: i for insert money, s for select item, q for quit."
            + "\n\n============================================");

    if ("q".equals(soption)) {   // If user chooses q: quit 
        JOptionPane.showMessageDialog(null, "Have a Nice Day!");
        System.exit(0);     // terminate application
    }
    if ("i".equals(soption)) {   // if user chooses i: insert money
        JOptionPane.showInputDialog(
                "=============================" 
                + "\nPlease enter some money (in pence)" 
                + "\n=============================");   // Inserting money
        insertMoney = Integer.parseInt(sinsertMoney);   // Parsing for calculations
    }
    if ("s".equals(soption)) {    // if user chooses s: select item
    }
}

Answer 1

我看不到您在何处声明了 sinsertMoney，但您似乎忘记将调用 JOptionPane.showInputDialog 的结果分配给某些内容，因此，当您尝试解析该值时，该值仍然为空。

试试这个:

sinsertMoney = JOptionPane.showInputDialog(
    "=============================" 
    + "\nPlease enter some money (in pence)" 
    + "\n=============================");   // Inserting money
insertMoney = Integer.parseInt(sinsertMoney);