添加 ScrollPane 使我的 JTextArea 消失

Question

If I have the scrollbar, the JTextArea just vanishes. Without it, everything is fine. Can someone please explain this to me? And how to fix it!

Also, as an aside, is it possible to change the color or set a border on the scrollpane?

Here is the relevant code:

        //Text Container
    JPanel textCon = new JPanel();
    textCon.setOpaque(false);
    textCon.setLayout(new GridLayout(1,3));
    add(textCon);

    //Left Filler
    JPanel left = new JPanel();
    left.setOpaque(false);
    textCon.add(left);

    //Text area
    mainText = new JTextArea("SAMPLE");
    mainText.setOpaque(true);
    mainText.setSize(50,30);
    mainText.setLineWrap(true);
    mainText.setWrapStyleWord(true);
    textCon.add(mainText);

    //Set textAre fonts, colors, border/padding
    mainText.setBorder(BorderFactory.createCompoundBorder(BorderFactory.createLineBorder(Color.GREEN), BorderFactory.createEmptyBorder(10, 10, 10, 10)));
    mainText.setFont(new Font("sansserif", Font.BOLD, 10));
    mainText.setForeground(Color.GREEN);
    mainText.setBackground(Color.BLACK);

    //Scroll Bar
    scroller = new JScrollPane(mainText);
    scroller.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
    mainText.add(scroller);

And here is the rest of it, just in case!

import java.awt.*;
import java.awt.event.*;
import java.awt.Toolkit.*;
import javax.swing.*;
import java.io.*;
import javax.swing.border.*;
import java.util.*;

class ProjectMain extends JFrame
{
//Declare String/Array for mainText
String output = "";
String [] hero;
int page = 0;
JTextArea mainText;
JScrollPane scroller;

public ProjectMain()
{
    //Set Background
    setTitle("JLA Viewer");
    setSize(1920,1080);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);
    setContentPane(new JLabel(new ImageIcon("bg.png")));
    setLayout(new GridLayout(3,1));

    //Refresh Background
    setSize(1919,1079);
    setSize(1920,1080);

    //Label Container
    JPanel labelCon = new JPanel();
    labelCon.setOpaque(false);
    labelCon.setLayout(new BorderLayout());
    add(labelCon);

    //Top Label
    JLabel topLabel = new JLabel("JLA Profile Viewer");
    topLabel.setHorizontalAlignment(SwingConstants.CENTER);
    topLabel.setForeground(Color.GREEN);
    topLabel.setOpaque(false);
    topLabel.setFont(new Font("sansserif", Font.BOLD, 30));
    labelCon.add(BorderLayout.NORTH,topLabel);

    //Logo
    ImageIcon logo = new ImageIcon("logo.jpg");
    JLabel logoLabel = new JLabel();
    logoLabel.setHorizontalAlignment(SwingConstants.CENTER);
    logoLabel.setIcon(logo);
    labelCon.add(BorderLayout.SOUTH,logoLabel);

    //Text Container
    JPanel textCon = new JPanel();
    textCon.setOpaque(false);
    textCon.setLayout(new GridLayout(1,3));
    add(textCon);

    //Left Filler
    JPanel left = new JPanel();
    left.setOpaque(false);
    textCon.add(left);

    //Text area
    mainText = new JTextArea("SAMPLE");
    mainText.setOpaque(true);
    mainText.setSize(50,30);
    mainText.setLineWrap(true);
    mainText.setWrapStyleWord(true);
    textCon.add(mainText);

    //Set textAre fonts, colors, border/padding
    mainText.setBorder(BorderFactory.createCompoundBorder(BorderFactory.createLineBorder(Color.GREEN), BorderFactory.createEmptyBorder(10, 10, 10, 10)));
    mainText.setFont(new Font("sansserif", Font.BOLD, 10));
    mainText.setForeground(Color.GREEN);
    mainText.setBackground(Color.BLACK);

    //Scroll Bar
    scroller = new JScrollPane(mainText);
    scroller.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
    mainText.add(scroller);

    //Right Filler
    JPanel right = new JPanel();
    right.setOpaque(false);
    textCon.add(right);

    //Button Container
    JPanel buttonContainer = new JPanel();
    buttonContainer.setOpaque(false);
    add(BorderLayout.SOUTH,buttonContainer);

    //PREV Button
    JButton prev = new JButton("PREV");
    prev.setOpaque(false);
    ActionListener PrevList = new PrevButton(); //Call Button Listener
    prev.addActionListener(PrevList);
    buttonContainer.add(prev);

    //EXIT Button
    JButton exit = new JButton("EXIT");
    exit.setOpaque(false);
    ActionListener ExitList = new ExitButton(); //Call Button Listener
    exit.addActionListener(ExitList);
    buttonContainer.add(exit);

    //NEXT Button
    JButton next = new JButton("NEXT");
    next.setOpaque(false);
    ActionListener NextList = new NextButton(); //Call Button Listener
    next.addActionListener(NextList);
    buttonContainer.add(next);

    //File Handling
    try
    {
        File inputFile = new File ("ProjectInputFile.txt");
        Scanner scanner = new Scanner(inputFile);

        while(scanner.hasNextLine())
        {
            output = output + (scanner.nextLine() + "\n");
        }
    }
    catch(IOException ioe)
    {

    }

    //Add split strings to array
    hero = output.split("@");
}

//Prev button event listener
public class PrevButton implements ActionListener
{
    public void actionPerformed(ActionEvent e)
    {
        page = page - 1;
        if(page < 0)
        {
            page = hero.length;
        }
        mainText.setText(hero[page]);
    }
}

//Exit button event listener
public class ExitButton implements ActionListener
{
    public void actionPerformed(ActionEvent e)
    {
        setVisible(false);
        dispose();
        System.exit(0);
    }
}

//Next button event listener
public class NextButton implements ActionListener
{
    public void actionPerformed(ActionEvent e)
    {
        page++;
        if(page > (hero.length))
        {
            page = 0;
        }
        mainText.setText(hero[page]);
    }
}

public static void main(String args[])
{
    new ProjectMain();
}

}

Answer 1

This line

mainText.add(scroller);

attempts to add a JScrollPane to a JTextArea . You have already set the ViewPortView of the JScrollPane so this line is unnecessary.

You will still need to add the JSrolllPane :

textCon.add(scroller);

Also make sure to call JFrame#setVisible after all components have been added.

setVisible(true);

is it possible to change the color or set a border on the scrollpane?

Sure. Instead of setting the border on the JTextArea mainText , set it on the JScrollPane .

Side notes:

• Don't silently catch IOException without showing the exception content
• JFrames are typically used directly rather than extending

Answer 2

You just need to setBounds(x,y,z,w) to your JScrollPane and not your JTextArea . Then add your JSrcollPane to your JFrame of your JPanel .