可以帮忙看看是哪里出错了吗

nimifur 2018-12-19 10:03:24

package cn.itcast.swing.demo;



import java.awt.BorderLayout;

import java.awt.EventQueue;



import javax.swing.JFrame;

import javax.swing.JPanel;

import javax.swing.border.EmptyBorder;

import javax.swing.JTextField;

import javax.swing.JButton;

import javax.swing.JTextArea;

import java.awt.event.ActionListener;

import java.io.File;

import java.awt.event.ActionEvent;



public class MyWindow extends JFrame {



	private static final String LINE_SEPARATOR = System.getProperty("line.separator");

	private JPanel contentPane;

	private JTextField textField;

	private JButton button;

	private JTextArea textArea;



	/**

	 * Launch the application.

	 */

	public static void main(String[] args) {

		EventQueue.invokeLater(new Runnable() {

			public void run() {

				try {

					MyWindow frame = new MyWindow();

					frame.setVisible(true);

				} catch (Exception e) {

					e.printStackTrace();

				}

			}

		});

	}



	/**

	 * Create the frame.

	 */

	public MyWindow() {

		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

		setBounds(100, 100, 450, 300);

		contentPane = new JPanel();

		contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));

		setContentPane(contentPane);

		contentPane.setLayout(null);

		

		textField = new JTextField();

		textField.setBounds(10, 10, 254, 30);

		contentPane.add(textField);

		textField.setColumns(10);

		

		JButton btnNewButton = new JButton("New button");

		btnNewButton.addActionListener(new ActionListener() {

			public void actionPerformed(ActionEvent e) {

				buttonActionPerformed(e);

			}

		});

		btnNewButton.setBounds(302, 10, 93, 30);

		contentPane.add(btnNewButton);

		

		JTextArea textArea = new JTextArea();

		textArea.setBounds(10, 53, 383, 198);

		contentPane.add(textArea);

	}



	private void buttonActionPerformed(ActionEvent e) {

		showDir();

	}



	private void showDir() {

		

		/*

		 * 通过点击按钮获取文本框中目录，

		 * 将目录中的内容显示在文本区域中。

		 */

		

		String dir_str = textField.getText();

		File dir = new File(dir_str);

		

		if(dir.exists() && dir.isDirectory()){

			textArea.setText("");

			String[] names = dir.list();

			

			for(String  name : names){

				textArea.append(name+LINE_SEPARATOR);

			}

		}

	}

			

}

一直提示这个错误：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at cn.itcast.swing.demo.MyWindow.showDir(MyWindow.java:85)
at cn.itcast.swing.demo.MyWindow.buttonActionPerformed(MyWindow.java:71)
at cn.itcast.swing.demo.MyWindow.access$0(MyWindow.java:70)
at cn.itcast.swing.demo.MyWindow$2.actionPerformed(MyWindow.java:59)

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