如何在mouseListener中删除和创建对象？

Question

I want to make a mouse event that calls my delete method, which will delete an object, a JScrollPane and all its components and then with another method call create another JScrollPane.

I did that. If I run it outside my mouse event like get_more() and make_it() it works, but if I do it in a mouseListener it doesn't work. I've ve tried revalidate and repaint() , but nothing. So what is the problem?

    import javax.swing.JTextArea;
    import javax.swing.JLabel;
    import javax.swing.SwingConstants;

    import java.io.FileReader;
    import javax.swing.JFrame;
    import javax.swing.JPanel;
    import java.awt.Graphics;
    import javax.swing.JTextArea;
    import javax.swing.JButton;
    import java.awt.BorderLayout;
    import java.awt.Font;
    import java.awt.event.*;
    import java.awt.GridLayout;
    import java.awt.Color;
    import java.awt.FlowLayout;
    import javax.swing.JScrollPane;
    import java.io.File;
    import java.util.Scanner;
    import java.awt.Dimension;
    import java.io.LineNumberReader;
    public class getmessage 
    extends JFrame
    {
        getter g1;
        getmessage()
        {

            try{
                g1 = new getter("Ionescu Gabriel","Vladimir Alexandru");

                add(g1.scrollpane);
            }
            catch(Exception eos)
            {
                System.out.println("File not found");

            }

        }
        public static void main(String[] args)
        {
            getmessage rama = new getmessage();
            rama.setTitle("A Good Title");
            rama.setLocationRelativeTo(null);
            rama.setSize(400,400);
            rama.setVisible(true);
        }
    }
    class
    getter
    {
        StringBuilder text;
        String sir;
        JPanel panou_1;
        JTextArea[] text_fragmet;
        JPanel panou;
        JScrollPane scrollpane;
        JPanel[] panou_set;
        int  number_message = 20;
        Scanner scan;
        File message;
        String name;
        JLabel  more;
        String name_messager;
        JPanel panou2; 

        getter(String name,String name_messager)
        throws Exception
        {
            this.name = name;
            this.name_messager = name_messager;
            message = new File(""+name+"/"+name_messager);

            scan = new Scanner(message);
            text = new StringBuilder();
            panou = new JPanel();
            text_fragmet = new JTextArea[5000];
            panou_set = new JPanel[5000];
            sir = new String();

            panou2 = new JPanel();
            panou2.setLayout(new FlowLayout(FlowLayout.CENTER,20,10));
            more = new JLabel("Show More Messages");

            more.setBackground(Color.white);
            panou2.add(more);

            make_it();

            more.addMouseListener(new MouseListener(){
                public void mousePressed(MouseEvent moe)
                {

                }
                public void mouseExited(MouseEvent moe)
                {

                }
                public void mouseEntered(MouseEvent moe)
                {
                    Color c1  = new Color(20,20,20);
                    more.setBackground(Color.red);
                }
                public void mouseReleased(MouseEvent moe)
                {
                    more.setBackground(Color.white);

                }
                public void mouseClicked(MouseEvent moe)
                {
                                   get_more();
                    make_it();


                    scrollpane.repaint();
                    scrollpane.revalidate();
                    System.out.println("Clicked");
                }
            });


        //  get_more();\
        //  make_it() -> Works just fine


        }
    public void init()
    {
        panou_1 = new JPanel();
        panou_1.setLayout( new BorderLayout());
        panou_1.add(panou2 , BorderLayout.NORTH);
        panou_1.add(panou,BorderLayout.CENTER);


        scrollpane = new JScrollPane(panou_1);

        scrollpane.revalidate();
        scrollpane.repaint();
        panou_1.revalidate();
        panou_1.repaint();
        panou.repaint();
        panou.revalidate();
        scrollpane.setVisible(false);
        scrollpane.setVisible(true);

        scrollpane.setBackground(Color.white);
        scrollpane.setHorizontalScrollBar(null);

    }
    public void make_it()
    {


        if(message.exists())
        {
            int i = 0;
            while(scan.hasNext() && i < number_message)
            {
                sir = scan.nextLine();

                if(i % 2 == 0)
                {

                    text_fragmet[i] = new JTextArea("");
                    text_fragmet[i].setText(sir+": ");
                    text_fragmet[i].setFont(new Font("SansSerif",Font.BOLD, 12));

                    Font f1 = new Font("SansSerif",Font.PLAIN ,12);
                    panou_set[i] = new JPanel();
                    panou_set[i].setLayout(new FlowLayout(FlowLayout.RIGHT));
                    panou_set[i].add(text_fragmet[i]);
                    text_fragmet[i].setWrapStyleWord(true);
                    text_fragmet[i].setLineWrap(true);

                }
                else
                {
                    text_fragmet[i] = new JTextArea("");

                    text_fragmet[i].setText(sir);
                    text_fragmet[i].setFont(new Font("Angelic War",Font.PLAIN, 12));
                    panou_set[i] = new JPanel();
                    panou_set[i].setLayout(new FlowLayout(FlowLayout.LEFT));
                    panou_set[i].add(text_fragmet[i]);
                    text_fragmet[i].setWrapStyleWord(true);
                    text_fragmet[i].setLineWrap(true);
                    text_fragmet[i].setColumns(30);

                }

                panou.add(panou_set[i]);

                i++;
            }      panou.setLayout(new GridLayout( (i-2)/2 +1 ,2)); 
        scan.close();
        }
        else
        {
            System.out.println("File not found");
        }
        panou.setBackground(Color.white);


        init();
        scrollpane.revalidate();
        scrollpane.repaint();

    }
    public void get_more()

    {

        scrollpane = null;

        text_fragmet = null;
        panou = null;
        scrollpane = null;
        panou_set = null;

        scan = null;
        message = null;
        System.gc();

        message = new File(""+name+"/"+name_messager);
        try {
        scan = new Scanner(message);
        }
        catch(Exception oe)
        {

        }
        text = new StringBuilder();
        panou = new JPanel();
        text_fragmet = new JTextArea[5000];
        panou_set = new JPanel[5000];
        sir = new String();
        number_message = number_message + 20;

        panou2 = new JPanel();
        panou2.setLayout(new FlowLayout(FlowLayout.CENTER,20,10));
        more = new JLabel("Show More Messages");

        more.setBackground(Color.white);
        panou2.add(more);
        more.addMouseListener(new MouseListener(){
            public void mousePressed(MouseEvent moe)
            {

            }
            public void mouseExited(MouseEvent moe)
            {

            }
            public void mouseEntered(MouseEvent moe)
            {
                Color c1  = new Color(20,20,20);
                more.setBackground(Color.red);
            }
            public void mouseReleased(MouseEvent moe)
            {
                more.setBackground(Color.white);
            }
            public void mouseClicked(MouseEvent moe)
            {
                get_more();
                make_it();
                System.out.println("Clicked");

            }
        });
    }
    }

Answer 1

which will delete an object, a JScrollPane and all its components and then with another method call create another JScrollPane.

Don't do that. Removing and adding components at run time should be avoided when possible.

In this case it is easy to do what you want, just reset the viewport of the scrollpane:

scrollPane.setViewportView( yourNewPanelFullOfComponents );

There is no need for revalidate() or repaint().