java - 1 个错误! "Main.java:30: error: cannot find symbol"

Question

我似乎无法让我为 Java 编程类(class)编写的代码正常工作。

/*Coby Bushong
Java Programming
Professor Lehman
August 9th 2014*/

import java.util.Scanner; // Needed for the Scanner class

/*This program will calculate the commission of a stock broker
at a 2% commission given the number of shares at a contant rate.*/

public class StockCommission 
{
   public static void main(String[] args)
   {
      //Constants
      final double STOCK_VALUE = 21.77;       //price per share
      final double BROKER_COMMISSION = 0.02;  //broker commission rate

      //variables
      double shares;     //To hold share amount
      double shareValue; //To hold total price of shares
      double commission; //To hold commission
      double total;      //To hold total cost

      //create scanner for keyboard input
      Scanner Keyboard = new Scanner(System.in);

      //creates dialog box for user input
      String inputShares;
      inputShares = JOptionPane.showInputDialog(null, "How many stocks do you own?");
      shares = Integer.parseInt(inputShares);

      //calculate total
      shareValue = shares * STOCK_VALUE;

      //calculate commission
      commission = shareValue * BROKER_COMMISSION;

      //calculate total
      total = commission + shareValue;

      //display results
      System.out.println("Shares Owned:" + shares);
      System.out.println("Value of Shares:         $" + shareValue);
      System.out.println("Comission:         $" + commission);
      System.out.println("Total:       $" + total);
   }
}

我收到此错误:

Errors: 1

StockCommission.java:30: error: cannot find symbol
  inputShares = JOptionPane.showInputDialog(null, "How many stocks do you own?");
                ^

Answer 1

在 Java 中，您必须指定要在哪里查找类。在这里，该类是JOptionPane。它位于 javax.swing 包中。

您可以在here中阅读有关使用包的信息。 。基本上，你必须要么

• 使用完全限定的类名:

  inputShares = javax.swing.JOptionPane.showInputDialog(null, "How many stocks do you own?");
  

• 在文件顶部导入类或整个包:

  import javax.swing.JOptionPane;
  

  或

  import javax.swing.*;
  

  一般考虑后一种导入整个包的方法bad practice ，所以我不建议这样做。