How do I resize a JScrollPane within a JFrame? And how do I read from a file in Java?

问题

I have a song library, and I would like this selection list to only be on the left hand side of the window because I want to put other information about the song on the righthand side. I'm not sure how to change the size of JScrollPane, which is inside the JFrame.

In this library, I want to be able to import the songs stored in a file to my song library. Right now, I have an array within my code, but I want to be able to read from a text file instead of using this approach. In the file, I want to be able to store artist and album information about the song, but I don't want it to display in the song list.

    String songs[] = {"Song1", "Song2", "Song3", "Song4", "Song5"};
    JList list = new JList(songs);

    public SongLib(){

        JFrame songLibrary = new JFrame("Song Library");
        songLibrary.setLocationRelativeTo(null);
        songLibrary.setResizable(true);
        songLibrary.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

        list.addListSelectionListener(new ListSelectionListener(){
            public void valueChanged(ListSelectionEvent evt){
                int i = list.getSelectedIndex();
                if (i != -1)
                    System.out.println("Selected: " + songs[i]);
                else
                    System.out.println("Choose a song");    
            }
        });

        JScrollPane JSPane = new JScrollPane(list);
        JSPane.setPreferredSize(new Dimension(100,100));
        songLibrary.add(JSPane);
        songLibrary.setSize(400,400);
        songLibrary.setVisible(true);
    }

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

回答1:

1. Stop calling (for the rest of your entire life) setPreferredSize(). Meaning that this call: JSPane.setPreferredSize(new Dimension(100,100)); should definitely be removed.
2. If you want to have 2 panels side-by-side with a draggable separator: use JSplitPane. If you don't want the draggable divider, use a JPanel with an appropriate LayoutManager (GridBagLayout may be a good choice)
3. Reading from a file is pretty easy, just make a search on SO and you will find hundreds of response. If you want to parse csv-files, there are some libraries around that can help you do that. Eventually, if you consider making this an application for a while, there are some small pure-java, embeddable, databases which will do a much better job at reading/storing/searching information than a simple text-file.
4. Learn the Java naming conventions and stick to them: variables always start with a lower-case letter.

回答2:

In addition to @Guillaume Polet's good advice, setVisibleRowCount() may be useful to you going forward.

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JScrollPane;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;

/** @see https://stackoverflow.com/a/14801908/230513 */
public class SongLib {

    String songs[] = {"Song1", "Song2", "Song3", "Song4", "Song5"};
    JList list = new JList(songs);

    public SongLib() {

        JFrame songLibrary = new JFrame("Song Library");
        songLibrary.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        list.setVisibleRowCount(4);
        list.addListSelectionListener(new ListSelectionListener() {

            @Override
            public void valueChanged(ListSelectionEvent evt) {
                int i = list.getSelectedIndex();
                if (i != -1) {
                    System.out.println("Selected: " + songs[i]);
                } else {
                    System.out.println("Choose a song");
                }
            }
        });

        JScrollPane JSPane = new JScrollPane(list);
        songLibrary.add(JSPane);
        songLibrary.pack();
        songLibrary.setLocationRelativeTo(null);
        songLibrary.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new SongLib();
            }
        });
    }
}

回答3:

For 1., take a look at layouting in Java, especially the GridBagLayout. http://docs.oracle.com/javase/tutorial/uiswing/layout/gridbag.html

For 2: Reading and writing from / into files is made by using File-Objects and Inout/Output-Streams. But this is a very low level way to do this. I think you should consider using an XML file. Take a look at JAXB

来源：https://stackoverflow.com/questions/14801759/how-do-i-resize-a-jscrollpane-within-a-jframe-and-how-do-i-read-from-a-file-in