java - 我使用解析正确吗？

Question

据我所知，我做得对(但显然不是)我正在尝试将字符串更改为 double ，因为我无法从 JPane 获得 double 。它给了我一个对象未​​初始化错误。我该如何修复它？

import javax.swing.JOptionPane;

    public class jwindows {
    public static void main (String args[]) {

        double a, b, c;
        double sum = a + b + c;
        double product = a * b * c ;
        double avarge = a * b * c / 3;

    String stringA = JOptionPane.showInputDialog
            (null, "Please enter first number");
        a = Double.parseDouble(stringA);

    String stringB = JOptionPane.showInputDialog
            (null, "Please enter second number: ");
        b = Double.parseDouble(stringB);

    String stringC = JOptionPane.showInputDialog
            (null, "Please enter third number: ");  
        c = Double.parseDouble(stringC);

        JOptionPane.showInternalMessageDialog
        (null, "The sum of the 3 numbers is " + sum);

        JOptionPane.showInternalMessageDialog
        (null, "The avarge of the 3 numbers is " + avarge);

        JOptionPane.showInternalMessageDialog
        (null, "The sum of the 3 numbers is " + product);
    }
}

Answer 1

double a, b, c;
double sum = a + b + c;
double product = a * b * c ;
double avarge = a * b * c / 3;

您刚刚定义了变量，但没有初始化它们。获取所有 a、b、c 值后将它们移至右下方。

还有一件事:将 showInternalMessageDialog 更改为 showMessageDialog，因为您根本没有父组件。