Question

据我所知，我做得对（显然不是这样）我正在尝试将字符串更改为双打，因为我无法从JPane获得双倍。它给了我一个没有初始化错误的对象。我该如何解决？

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。在获得a，b，c的所有值后，将它们向右移动。

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

Answer 2

变量a，b，c尚未初始化（且不包含任何值），因此sum，product和{{ 1}}无法计算。要解决此问题，请在解析avarage，sum，product之后移动avarge，a和b。像这样：

Answer 3

你不会得到变量 sum，averge和product的预期值。你在开头计算它的值：

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

你必须在这里得到编译错误，因为a，b和c是在使用之前未初始化的局部变量。因此编译器会在这种情况下抛出错误。即使将其初始化为某个值，也必须在从showInputDialog为这些变量赋值后计算sum，averge和prodcut的值。

尝试使用：

sum = a+b+c;

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

     averge = (a+b+c)/3;
    JOptionPane.showInternalMessageDialog
    (null, "The avarge of the 3 numbers is " + avarge);
    product = a*b*c;
    JOptionPane.showInternalMessageDialog
    (null, "The sum of the 3 numbers is " + product);

我使用解析权吗？

3 个答案: