如何在Java中解决"令牌上的语法错误"否则""？

Question

我是新来的,但让我们直接回答这个问题:当我为类项目计算器编写以下代码时,我遇到了"令牌错误".这是完整的错误消息:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
Syntax error on token "else", delete this token

at calculatorApplet.main(calculatorApplet.java:42)

我写了这段代码:

import java.util.Scanner;
import javax.swing.JOptionPane;
public class calculatorApplet
{
    Scanner sc = new Scanner(System.in);
    public static void main(String[] args)
    {
        JOptionPane.showMessageDialog(null, "Welcome to the Calculator!");
        String option = JOptionPane.showInputDialog(null, "Which calculator mode do you want?");
        if (option.equals("Addition"))
        {
            Double add1 = Double.parseDouble(JOptionPane.showInputDialog(null, "Okay type the first number(s) of your addition problem."));
            Double add2 = Double.parseDouble(JOptionPane.showInputDialog(null, "Now type the second number(s) of your addition problem."));
            Double preAdd = add1+add2;
            Double Add = preAdd;
            JOptionPane.showMessageDialog(null, "The sum is " + Add + ".");
        }
        else
        {
            JOptionPane.showMessageDialog(null, "Huh?");
        }
        if (option.equals("Subtraction"))
        {
            Double sub1 = Double.parseDouble(JOptionPane.showInputDialog(null, "Okay type the first number(s) of your subtraction problem."));
            Double sub2 = Double.parseDouble(JOptionPane.showInputDialog(null, "Now type the second number(s) of your subtraction problem."));
            Double preSub = sub1-sub2;
            Double Sub = preSub;
            JOptionPane.showMessageDialog(null, "The difference is " + Sub + ".");
        }
        else
        {
            JOptionPane.showMessageDialog(null, "Huh?");
        }
        if (option.equals("Multiplication"));
        {
            Double mult1 = Double.parseDouble(JOptionPane.showInputDialog(null, "Okay type the first number(s) of your multiplication problem."));
            Double mult2 = Double.parseDouble(JOptionPane.showInputDialog(null, "Now type the second number(s) of your multiplication problem."));
            Double preMult = mult1*mult2;
            Double Mult = preMult;
            JOptionPane.showMessageDialog(null, "The product is " + Mult + ".");
        }
        else //Here is the error.
        {
            JOptionPane.showMessageDialog(null, "Huh?");
        } //Here ends the error.
        if (option.equals("Division"))
        {
            Double div1 = Double.parseDouble(JOptionPane.showInputDialog(null, "Okay type the first number(s) of your division problem."));
            Double div2 = Double.parseDouble(JOptionPane.showInputDialog(null, "Now type the second number(s) of your division problem."));
            Double preDiv = div1/div2;
            Double Div = preDiv;
            JOptionPane.showMessageDialog(null, "The quotient is " + Div + ".");
        }
        else
        {
            JOptionPane.showMessageDialog(null, "Huh?");
        }
        //End of if statements.
    } 

}

这是代码,我评论了令牌错误的区域.也许解决方案在我脸上.我希望我的代码是一个计算器,所以如果你们可以修复我的代码而不与数学运算冲突.谢谢,我感谢任何帮助.

Answer 1

;从这里删除行尾:

if (option.equals("Multiplication"));

Answer 2

问题是之后的分号if.

语法是if ( 条件 ) 表达式或块式 { else 表达式或块式 }

因为;是一个空表达式,所以这适用于if子句,并且在then子句中没有任何反应 - 在你的情况下,语法上没有else子句,因为你的if语句语句以分号结尾,后跟一个简单的块.然后,标记器检测到悬空else标记并进行投诉.

Answer 3

在错误发生之前的If语句末尾有一个分号.

if (option.equals("Multiplication"));