java 判断null

来源：百度知道 编辑：UC知道 时间：2024/06/07 17:55:06
info1 = JOptionPane.showInputDialog(null,msg,text);当我点击取消时，返回值为空，出现了以下错误，请问这是为什么啊。
--------------------Configuration: <Default>--------------------
Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: null

at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispat

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

class Mdialog extends JFrame implements ActionListener {
JLabel jlb = new JLabel("计算 1+2+3+......+n的和");

int number, result;

Mdialog()

{
super("演示输入对话框");
setSize(150, 150);

Container con = getContentPane();
con.setLayout(new BorderLayout());
JButton jbtn = new JButton("从对话框输入数n");
con.add(jbtn, BorderLayout.NORTH);
con.add(jlb, BorderLayout.CENTER);
jbtn.addActionListener(this);
validate();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
}

public void actionPerformed(ActionEvent e) {
String msg = " 请输入n的值：";
String text = "100";
try{
String temp = JOptionPane.showInputDialog(null,msg,text);
number = Integer.parseInt(temp);
}catch(Exception e1)