java - 为什么我的 JOptionPane.showMessageDialog 不工作？

Question

我是一名初级程序员，我为我的学校类(class)写了这篇文章。但不知何故，即使是我在 displaypay() 下的 JOptionPane.showMessageDialog 也无法正常工作!!!我预计会弹出一个消息框，但在我输入每天的小时数后，没有任何反应!它甚至没有跳过该部分，整个程序只是暂停!我感到很困惑!相反，如果我使用 System.out.println()，它工作正常。

我也不想为 displaypay() 做 System.out.println，我必须使用 showMessageDialog。

 package payroll.program;

 import java.util.Scanner;
 import javax.swing.JOptionPane; //imports

 class Employee
{
int hourlypay;
int totalhours = 0;
String name; //variables

void getname()
{
    Scanner scan = new Scanner(System.in);

    System.out.println("What is this employee's name?");
    name = scan.next(); //gets name
}

void calculatepay()
{
    int[] hours = new int[5]; //creates array for hours

    Scanner scan = new Scanner(System.in);

    System.out.println("How much is " + name + " paid per hour?");
    hourlypay = scan.nextInt(); //gets hourly pay

    for (int i = 0; i < 5; i++)
    {
        System.out.println("How many hours did " + name + " work on day " + (i + 1) + "?");
        hours[i] = scan.nextInt(); //gets hour on each day

        totalhours = totalhours + hours[i]; //adds hours up
    }
}
void displaypay()
{
    JOptionPane.showMessageDialog(null, "You have to pay " + " $" + totalhours * hourlypay + " to " + name + "!"); //displays total pay
}
 }

 public class PayrollProgram {

    public static void main(String[] args) {

    int numberofemployees; //variable for # of employees

    System.out.println("Welcome to the Payroll Program!"); //welcomes user

    Scanner scan = new Scanner(System.in);
    System.out.println("How many employees do you have?");
    numberofemployees = scan.nextInt(); //gets input for # of employees

    Employee[] ArrayofEmployees = new Employee[numberofemployees]; //creates array of employees with the same size as the number of employees

    for (int i = 0; i < numberofemployees; i++)
    {
        ArrayofEmployees[i] = new Employee(); //creates an Employee for each space in the array
    }

    for (int i = 0; i < numberofemployees; i++)
    {
        ArrayofEmployees[i].getname();
        ArrayofEmployees[i].calculatepay();
        ArrayofEmployees[i].displaypay(); //runs functions in class Employee for each employee
    }
}

这是我的程序，JOptionPane.showMessageDialog 不工作。

请帮忙!

Answer 1

当您尝试显示 swing 组件时，您应该从事件分派(dispatch)线程执行此操作。否则，您将无法获得可靠的结果。因此，在这种情况下，将所有代码包装在 main 中，调用 SwingUtilities.invokeLater。 :

public static void main(String[] args) {
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            int numberofemployees; //variable for # of employees

            System.out.println("Welcome to the Payroll Program!"); //welcomes user

            Scanner scan = new Scanner(System.in);
            System.out.println("How many employees do you have?");
            numberofemployees = scan.nextInt(); //gets input for # of employees

            Employee[] ArrayofEmployees = new Employee[numberofemployees]; //creates array of employees with the same size as the number of employees

            for (int i = 0; i < numberofemployees; i++) {
                ArrayofEmployees[i] = new Employee(); //creates an Employee for each space in the array
            }

            for (int i = 0; i < numberofemployees; i++) {
                ArrayofEmployees[i].getname();
                ArrayofEmployees[i].calculatepay();
                ArrayofEmployees[i].displaypay(); //runs functions in class Employee for each employee
            }
        }
    });
}

可在此处找到更多信息:The Event Dispatch Thread .

特别注意，如果您无法从事件调度程序线程运行 Swing 组件，会发生什么情况:

Programs that ignore this rule may function correctly most of the time, but are subject to unpredictable errors that are difficult to reproduce.