尝试将csv文件打印到JTextArea时出现NullPointerException

Question

我的项目是读取文件，显示其详细信息，并将这些细节压缩到每个团队的排名系统中。我目前只是将这些细节输出到我创建的JTextArea中。

import java.util.ArrayList;
import java.util.Scanner;
import java.io.*;

import javax.swing.JFileChooser;
import javax.swing.JOptionPane;

public class CollegeFootballPlayoffManager 
{
    private ArrayList<Team> rank;
    private File newFile;
    private JFileChooser fileChooser;
    private Scanner input;
    StringBuilder sb;

    public CollegeFootballPlayoffManager() 
    {
        rank = new ArrayList<>();
    }

    public void openFile() throws Exception
  {
      fileChooser = new JFileChooser();
      try
     {
        if(fileChooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION)
        {
            newFile = fileChooser.getSelectedFile();
            input = new Scanner(newFile);
        }

        else
        {
        JOptionPane.showMessageDialog(null, "No file was selected");
        }
    }
    catch(Exception e)
    {
        e.printStackTrace();
    }
    input.close();
  }
  public void readFile()
  {
    sb = new StringBuilder();

    while(input.hasNext())
    {
        sb.append(input.nextLine());
        sb.append("\n");
    }
    input.close();
}
}

这是我在文件中读取的内容，然后将文件内容输出到JTextArea。

import javax.swing.*;

import java.awt.*;  
import java.awt.event.ActionEvent;  
import java.awt.event.ActionListener;   


public class UI extends JFrame 
{

private static final long serialVersionUID = 1L;
private final int width = 650;      
private final int height = 400;
private JButton rVotes, rTeams, sDetails, exit;
private JPanel topPanel;
private JTextArea text;

public UI()
{
    JOptionPane.showMessageDialog(null, "Select 'Read Votes' to begin... ");

    setTitle("College Football Playoff Selection");
    setSize(width, height);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    buildTop();
    add(topPanel, BorderLayout.NORTH);

    text = new JTextArea();
    text.setFont(new Font("Monospaced", Font.PLAIN,10));
    text.setBackground(Color.LIGHT_GRAY);
    text.setForeground(Color.BLACK);
    text.setBounds(150,100,150,10);
    text.setEditable(false);
    add(text);
}

private void buildTop()
{
    topPanel = new JPanel(new FlowLayout());
    topPanel.setBackground(Color.LIGHT_GRAY);
    rVotes = new JButton("Read Votes");
    rVotes.setActionCommand("V");
    rVotes.addActionListener(new ButtonListener());
    rTeams = new JButton("Rank Teams");
    rTeams.setActionCommand("R");
    rTeams.addActionListener(new ButtonListener());
    sDetails = new JButton("Show Details");
    sDetails.setActionCommand("S");
    sDetails.addActionListener(new ButtonListener());
    exit = new JButton("Exit");
    exit.setActionCommand("E");
    exit.addActionListener(new ButtonListener());

    topPanel.add(rVotes);
    topPanel.add(rTeams);
    topPanel.add(sDetails);
    topPanel.add(exit);
}

private class ButtonListener implements ActionListener
{
      public void actionPerformed(ActionEvent e)
      {
         switch(e.getActionCommand())
         {

            /** Only occurs when "V" button is clicked */

            case "V":
            CollegeFootballPlayoffManager read = new CollegeFootballPlayoffManager();

            try {
                read.openFile();
            } catch (Exception e1) 
            {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }

                break;
            /** Only occurs when "R" button is clicked */
            case "R":

                break;
            /** Only occurs when "S" button is clicked */
            case "S":
            CollegeFootballPlayoffManager show = new   CollegeFootballPlayoffManager();
                text.setText(show.sb.toString());
                break;
            /** Only occurs when "E" button is clicked */
            case "E":   
            System.exit(0);
                break;
         }

       }
}
public static void main(String[] args)
 {
    UI frame = new UI();        /** declare and instantiate a new UI object  */
    frame.setVisible(true);     /** Makes window visible */
}
}

这是我的GUI窗口，我收到了这段代码的错误。

    text.setText(show.sb.toString());