Question

每当我运行程序而不传入usDollarAmount或取消程序时，我都会收到异常...我使用swing组件来接受用户输入。该程序工作正常。

请告诉我如何处理这个......谢谢

THE Currency CALCULATOR
Exception in thread "main" java.lang.NullPointerException
at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
at sun.misc.FloatingDecimal.parseDouble(Unknown Source)
at java.lang.Double.parseDouble(Unknown Source)
at Currency.main(Currency.java:28)

import java.text.DecimalFormat;

import javax.swing.JOptionPane;

 public class Currency{

public static void main(String[] args)
{
    // declare and construct variables


    double usDollarAmount, poundsAmount,eurosAmount,rublesAmount;

    DecimalFormat twoDigits = new DecimalFormat("####.00");

    //print prompts and get input
    System.out.println("\tTHE Currency CALCULATOR");

    //print prompts and get input
    usDollarAmount = Double.parseDouble(JOptionPane.showInputDialog(null, "Enter your dollar amount:"));


     // calculations

    poundsAmount = 0.64 * usDollarAmount;
    eurosAmount = 0.91 * usDollarAmount ;
    rublesAmount = 61.73 * usDollarAmount ;

     // output
  JOptionPane.showMessageDialog(null, "YOUR DOLLAR AMOUNT OF  " + twoDigits.format(usDollarAmount) + " is equal to  " + twoDigits.format(eurosAmount)  + " euros"  + " ," + twoDigits.format(poundsAmount)  + " pounds"  + " " + " and " + twoDigits.format(rublesAmount) + " rubles"  );


System.exit(0);

}

}

Answer 1

首先将输入分配给变量，然后进行空检查。如果不为null则执行解析

String input = JOptionPane.showInputDialog(null, "Enter your dollar amount:");
if(input != null && !input.trim().isEmpty())
    usDollarAmount = Double.parseDouble();

有人可以告诉我如何在我的代码中处理java.lang.NullPointerException

1 个答案: