此问题在此处已有答案：

What is 'scope' in Java?（2个答案）
上个月关门了。
我是Java的新手，正在尝试写一个程序，询问你的姓名、收入、联邦和州的税率，然后计算出你应该缴纳多少税。它应该包括对话框。我的问题是：我已经完成了所有的代码并放入parseDouble（）方法，但是当我去计算时，Eclipse给了我一个错误（stateTaxRate不能解析为变量，它对fedTaxRate变量也做了同样的事情！我被卡住了。

import javax.swing.JOptionPane;
public class FedAndStateTaxes {

  public static void main(String[] args) {
    
    String yourName= JOptionPane.showInputDialog("What is your name?");
    JOptionPane.showMessageDialog(null, "Name: " + yourName);
    
    
    String yearlyIncome = JOptionPane.showInputDialog("What is your yearly income?");

    
    try {double num = Double.parseDouble(yearlyIncome); 
    JOptionPane.showMessageDialog(null, "Yearly Income: "+ num);
    
    }
    catch(NumberFormatException e){
    JOptionPane.showMessageDialog(null,"Error. Number input only please.");
    }
    
    
    String fTaxRate = JOptionPane.showInputDialog("Please enter your federal tax rate");
    
    
    try { double fedTaxRate = Double.parseDouble(fTaxRate);
    JOptionPane.showMessageDialog(null, "Federal Tax Rate: " + fedTaxRate +"%");
        
    }
    catch(NumberFormatException e){
        JOptionPane.showMessageDialog(null, "Error. Number input only please.");
    }
    
    String sTaxRate = JOptionPane.showInputDialog("Pleae enter your state tax rate");
    
    try { 
        double stateTaxRate = Double.parseDouble(sTaxRate);
        JOptionPane.showMessageDialog(null, "State Tax Rate: " + stateTaxRate + "%");
    }
    catch(NumberFormatException e) {
        JOptionPane.showMessageDialog(null,"Error. Number input only please");
    }
    

    double calculateIncome = (stateTaxRate);

字符串
我尝试在parseDouble（）方法中更改参数/变量名。我希望它能调用我转换成double的字符串变量，但它就是无法解析。