1個錯誤！ “ Main.java:30：錯誤：找不到符號”

Question

我似乎無法讓他為我的Java編程類編寫的代碼起作用。

/*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);
   }
}

我收到此錯誤：

Errors: 1

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

Answer 1

在Java中，您必須指定要在哪里找到一個類。 在這里，該類是JOptionPane 。 它位於javax.swing包中。

您可以在此處閱讀有關使用軟件包的信息 。 基本上，您必須要么

• 使用完全限定的類名：

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

• 將類或整個包導入文件頂部：

   import javax.swing.JOptionPane; 

  要么

   import javax.swing.*; 

  導入整個軟件包的后一種方法通常被認為是不好的做法 ，因此我不建議您這樣做。

Answer 2

您必須導入 JOptionPane類。 在文件頂部添加以下內容：

import javax.swing.JOptionPane;