java JScrollBar不工作

Question

我正在尝试将JScrollPane添加到JTextArea，但是当我添加它时，JPane不再显示我的textarea。如果没有JScrollPane，它会显示它，但是我无法显示从文件检索到的所有信息

这是我想用JScrollPane包装的textArea之一的代码

   public GUI_CWK()
{
    //frame details
    setSize(450,400);

    setLayout(null);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setTitle("H.o. | Location Database");
    setExtendedState(JFrame.MAXIMIZED_BOTH); 
    getContentPane().setBackground(Color.YELLOW);
    // Useing Lable to set a title for multiple buttons
    lbl2 = new JLabel();
    lbl2.setSize(420,85);
    lbl2.setLocation(15,0);
    lbl2.setEnabled(false);
    lbl2.setFont(new Font ("arial",5,17));
    lbl2.setText("Options to Manipulate with Data");
    add(lbl2);

    // Adding buttons to JFrame
    btn1 = new JButton("Add new entry");
    btn1.setSize(120,20);
    btn1.setLocation(7,80);
    btn1.addActionListener(this);
    add(btn1);

    btn2 = new JButton("Search");
    btn2.setSize(120,20);
    btn2.setLocation(7,110);
    btn2.addActionListener(this);
    add(btn2);

    btn3 = new JButton("Update Entry");
    btn3.setSize(120,20);
    btn3.setLocation(150,110);
    btn3.addActionListener(this);
    add(btn3);

    btn4 = new JButton("Print All");
    btn4.setSize(120,20);
    btn4.setLocation(150,80);
    btn4.addActionListener(this);
    add(btn4);

    btn5 = new JButton("Print Arrays");
    btn5.setSize(120,20);
    btn5.setLocation(7,140);
    btn5.addActionListener(this);
    add(btn5);

    btn6 = new JButton("Delete Entry");
    btn6.setSize(120,20);
    btn6.setLocation(300,80);
    btn6.addActionListener(this);
    add(btn6);

    btn7 = new JButton("Delete ALL");
    btn7.setSize(120,20);
    btn7.setLocation(300,110);
    btn7.addActionListener(this);
    add(btn7);

    lbl1 = new JLabel();
    lbl1.setSize(420,85);
    lbl1.setLocation(15,190);
    lbl1.setEnabled(false);
    lbl1.setFont(new Font ("arial",5,17));
    lbl1.setText("Extra Options");
    add(lbl1);

    btn8 = new JButton("Sort Data");
    btn8.setSize(160,20);
    btn8.setLocation(7,265);
    btn8.addActionListener(this);
    add(btn8);

    btn9 = new JButton("Open Text file");
    btn9.setSize(160,20);
    btn9.setLocation(7,300);
    btn9.addActionListener(this);
    add(btn9);

    btn11 = new JButton("Retrieve from text file");
    btn11.setSize(160,20);
    btn11.setLocation(240,265);
    btn11.addActionListener(this);
    add(btn11);

    btn12 = new JButton("Exit Program");
    btn12.setSize(160,20);
    btn12.setLocation(240,300);
    btn12.addActionListener(this);
    add(btn12);

    lbl3 = new JLabel();
    lbl3.setSize(420,85);
    lbl3.setLocation(15,340);
    lbl3.setEnabled(false);
    lbl3.setFont(new Font ("arial",5,17));
    lbl3.setText("Terminal Window");
    add(lbl3);
    // Adding textArea to display each user entered value
    textArea2 = new JTextArea(5, 20);
    textArea2.setEditable(false);
    textArea2.setSize(440,300);
    textArea2.setLocation(7,400);
    textArea2.setDisabledTextColor(Color.black);
    textArea2.setFont(new Font("arial",5,14));
    sp2 = new JScrollPane(textArea2);
    sp2.setVerticalScrollBarPolicy ( ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS );
    add(sp2);

    lbl4 = new JLabel();
    lbl4.setSize(420,40);
    lbl4.setLocation(570,10);
    lbl4.setEnabled(false);
    lbl4.setFont(new Font ("arial",5,17));
    lbl4.setText("Data Display");
    add(lbl4);

    textArea = new JTextArea(55, 50);
    textArea.setEditable(false);
    textArea.setSize(800,640);
    textArea.setLocation(560,60);
    textArea.setFont(new Font("arial",5,19));
    textArea.setDisabledTextColor(Color.black);
    sp = new JScrollPane(textArea);
    sp.setVerticalScrollBarPolicy ( ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS );
    add(sp);

    setVisible(true);
}

Answer 1

谢谢你们的帮助，我找到了答案。正如@matt告诉我的，我应该将大小和位置添加到JScrollPane而不是textArea。所以我做了，现在对我来说很有效

代码如下

---

 textArea2 = new JTextArea(5,20);
    textArea2.setEditable(false);
    textArea2.setDisabledTextColor(Color.black);
    textArea2.setFont(new Font("arial",5,14));
    sp2 = new JScrollPane(textArea2);
    sp2.setSize(440,300);
    sp2.setLocation(7,400);
    sp2.setVerticalScrollBarPolicy ( ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS );
    add(sp2);

Answer 2

我认为这应该解决你的问题

您会注意到，我删除了addActionListener()方法之间的this，因为您必须指定ActionListener要做什么

StartingPoint（主）类：

public class StartingPoint{
public static void main(String[] args){

    GUI_CWK gui_cwk = new GUI_CWK(); //Creates a new instance of "GUI_CWK".
    gui_cwk.setVisible(true); //You set the gui_cwk to visible.

}
}

GUI_CWK类：

import java.awt.Color;
import java.awt.Font;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.ScrollPaneConstants;

public class GUI_CWK extends JFrame{ 
private static final long serialVersionUID = 1L;

public GUI_CWK() {

    // frame details
    this.setSize(450, 400);

    JPanel panel = new JPanel();

    this.setLayout(null); /* Each time that you want to refer to the classyou are in, you say "this" */
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    this.setTitle("H.o. | Location Database");
    this.setExtendedState(JFrame.MAXIMIZED_BOTH);
    this.getContentPane().setBackground(Color.YELLOW);

    // Using labels to set a title for multiple buttons
    JLabel lbl2 = new JLabel(); /*Remember that you have to create the instances of an object by naming the class before the name of the instance */
    lbl2.setSize(420, 85);
    lbl2.setLocation(15, 0);
    lbl2.setEnabled(false);
    lbl2.setFont(new Font("arial", 5, 17));
    lbl2.setText("Options to Manipulate with Data");
    panel.add(lbl2);

    // Adding buttons to JFrame
    JButton btn1 = new JButton("Add new entry");
    btn1.setSize(120, 20);
    btn1.setLocation(7, 80);
    btn1.addActionListener(/* Insert ActionListener */);
    panel.add(btn1); //The button is added to the panel, so then the last one can be added to the JFrame at the end.

    JButton btn2 = new JButton("Search");
    btn2.setSize(120, 20);
    btn2.setLocation(7, 110);
    btn2.addActionListener(/* Insert ActionListener */);
    panel.add(btn2);

    JButton btn3 = new JButton("Update Entry");
    btn3.setSize(120, 20);
    btn3.setLocation(150, 110);
    btn3.addActionListener(/* Insert ActionListener */);
    panel.add(btn3);

    JButton btn4 = new JButton("Print All");
    btn4.setSize(120, 20);
    btn4.setLocation(150, 80);
    btn4.addActionListener(/* Insert ActionListener */);
    panel.add(btn4);

    JButton btn5 = new JButton("Print Arrays");
    btn5.setSize(120, 20);
    btn5.setLocation(7, 140);
    btn5.addActionListener(/* Insert ActionListener */);
    panel.add(btn5);

    JButton btn6 = new JButton("Delete Entry");
    btn6.setSize(120, 20);
    btn6.setLocation(300, 80);
    btn6.addActionListener(/* Insert ActionListener */);
    panel.add(btn6);

    JButton btn7 = new JButton("Delete ALL");
    btn7.setSize(120, 20);
    btn7.setLocation(300, 110);
    btn7.addActionListener(/* Insert ActionListener */);
    panel.add(btn7);

    JLabel lbl1 = new JLabel();
    lbl1.setSize(420, 85);
    lbl1.setLocation(15, 190);
    lbl1.setEnabled(false);
    lbl1.setFont(new Font("arial", 5, 17));
    lbl1.setText("Extra Options");
    panel.add(lbl1);

    JButton btn8 = new JButton("Sort Data");
    btn8.setSize(160, 20);
    btn8.setLocation(7, 265);
    btn8.addActionListener(/* Insert ActionListener */);
    panel.add(btn8);

    JButton btn9 = new JButton("Open Text file");
    btn9.setSize(160, 20);
    btn9.setLocation(7, 300);
    btn9.addActionListener(/* Insert ActionListener */);
    panel.add(btn9);

    JButton btn11 = new JButton("Retrieve from text file");
    btn11.setSize(160, 20);
    btn11.setLocation(240, 265);
    btn11.addActionListener(/* Insert ActionListener */);
    panel.add(btn11);

    JButton btn12 = new JButton("Exit Program");
    btn12.setSize(160, 20);
    btn12.setLocation(240, 300);
    btn12.addActionListener(/* Insert ActionListener */);
    panel.add(btn12);

    JLabel lbl3 = new JLabel();
    lbl3.setSize(420, 85);
    lbl3.setLocation(15, 340);
    lbl3.setEnabled(false);
    lbl3.setFont(new Font("arial", 5, 17));
    lbl3.setText("Terminal Window");
    panel.add(lbl3);

    // Adding textArea to display each user entered value
    JTextArea textArea2 = new JTextArea(5, 20);
    textArea2.setEditable(false);
    textArea2.setSize(440, 300);
    textArea2.setLocation(7, 400);
    textArea2.setDisabledTextColor(Color.black);
    textArea2.setFont(new Font("arial", 5, 14));

    JScrollPane sp2 = new JScrollPane(textArea2);
    sp2.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
    textArea2.add(sp2); //Here you add the scrollPanel to the textArea,
                        //in the original code you were adding it to the frame
    panel.add(textArea2);

    JLabel lbl4 = new JLabel();
    lbl4.setSize(420, 40);
    lbl4.setLocation(570, 10);
    lbl4.setEnabled(false);
    lbl4.setFont(new Font("arial", 5, 17));
    lbl4.setText("Data Display");
    panel.add(lbl4);

    JTextArea textArea = new JTextArea(55, 50);
    textArea.setEditable(false);
    textArea.setSize(800, 640);
    textArea.setLocation(560, 60);
    textArea.setFont(new Font("arial", 5, 19));
    textArea.setDisabledTextColor(Color.black);
    JScrollPane sp1 = new JScrollPane(textArea);
    sp1.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
    textArea.setVisible(true);
    textArea.add(sp1);
    panel.add(textArea);

    this.add(panel); //Everything which was added to the panel now is added to the frame.
    this.setDefaultCloseOperation(EXIT_ON_CLOSE);
}
}

Answer 3

下面是使用滚动窗格的示例

import javax.swing.*;
import java.awt.*;
public class ScrollPaneExample{
    public void buildGui(){
        JFrame frame = new JFrame("button and scrollpane");

        JButton button = new JButton("example");
        JTextArea area = new JTextArea(20, 20);
        //this is where we will place our components.
        //It has a flow layout by default.
        JPanel content = new JPanel(); 

        JScrollPane sp = new JScrollPane(area);
        content.add(button);
        content.add(sp);

        //this line limits the size of the scroll pane.
        sp.setPreferredSize(new Dimension(400, 60));

        //The frame will use our panel instead of the default one.
        frame.setContentPane(content);

        //sizes the frame to the content area.
        frame.pack();        

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
    public static void main(String[] args){
        EventQueue.invokeLater(()->{new ScrollPaneExample().buildGui();});
    }

}

主要区别在于我设置了内容窗格，以便了解其布局管理器。您似乎在手动设置所有尺寸，我很惊讶它能正常工作。你应该选择一个好的布局管理器pick one你想做什么就做什么

还要注意，这是一个将编译的最小示例