如果选择了第一个条目(Windows 10)，则摇摆JLIST会减慢速度

Question

目标：
用于任何目的。

问题：
如果选择了第一个条目，然后您清除模型并添加新内容，则无论您多久做一次，这都会非常慢。只有选择了另一个条目 - 不是第一个 - 行为将是快速=正常的。

解决方案：
每次清除模型之前，都要编程添加两个任意条目(两个，因为列表可能完全是空的(，然后选择具有最高有效索引的条目。

问题：
您可以复制该错误吗？它是已知的错误吗？如果没有，请有人发布它，以便openjdk修复？

测试环境：
标准Oracle Java版本下载JDK8202。
java version "1.8.0_202"
Java(TM) SE Runtime Environment (build 1.8.0_202-b08)
Java HotSpot(TM) 64-Bit Server VM (build 25.202-b08, mixed mode)
Windows 10 Home，版本1809(OS构建17763.437(
Intel(R(Core(TM(I7-6700K CPU @ 4.00 GHz 4.01 GHz

还用 OpenJDK 11
复制 openjdk version "11.0.2" 2019-01-15
OpenJDK Runtime Environment 18.9 (build 11.0.2+9)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.2+9, mixed mode)

SSCCE

此代码很小，因此甚至使用默认的lookandfeel。最初，我在使用l＆amp; f＆quot" Windows"时遇到了问题。

package jlistslowdownbugdemo;
import javax.swing.*;
import java.awt.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Random;


final public class Main {

    final private static boolean ENABLE_FIX = false;

    public static void main(final String[] args) {

        SwingUtilities.invokeLater(() -> {

            final DefaultListModel<String> valueListModel = new DefaultListModel<>();
            final JList<String> valueList = new JList<>(valueListModel);

            final DefaultListModel<String> keyListModel = new DefaultListModel<>();
            for (String key : Main.DATA.keySet()) {
                keyListModel.addElement(key);
            }
            final JList<String> keyList = new JList<>(keyListModel);

            keyList.addListSelectionListener(e -> {
                if (e.getValueIsAdjusting()) { // To prevent SUPER-slowdown when the bug kicks. Not an important measure, just for comfortable demoing.

                    // Workaround for the bug: Add two entries (two, because list may be entirely empty),
                    // and select the last available entry (in the worst case, this is the 2nd).
                    // Just so that one is selected that IS NOT THE FIRST.
                    // This problem AND fix occurred in Oracle JDK 8 and Open JDK 11.
                    if (ENABLE_FIX) {
                        valueListModel.addElement(null);
                        valueListModel.addElement(null); // Make sure you add something else instead of null if your GUI/JList setup requires it.
                        valueList.setSelectedIndex(valueListModel.size() - 1);
                    }

                    valueListModel.clear();
                    final String key = keyList.getSelectedValue();
                    if (key != null) {
                        for (String value : Main.DATA.get(key)) {
                            valueListModel.addElement(value);
                        }
                    }
                }
            });

            final JPanel contentPane = new JPanel(new GridLayout(1, 0, 0, 0));
            contentPane.add(new JScrollPane(keyList));
            contentPane.add(new JScrollPane(valueList));

            final JFrame window = new JFrame();
            window.setContentPane(contentPane);
            window.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
            window.setMinimumSize(new Dimension(1200, 1000));
            window.setLocationRelativeTo(null);
            window.setVisible(true);

            final String msg = "Click&drag in the left list. This rapidly changes the content of the right list.n" +
                    "n" +
                    "Now select any entry EXCEPT the first entry of the right list. Click&drag again in the left list,n" +
                    "it still works just as rapidly. Now click THE FIRST entry of the right list.n" +
                    "n" +
                    "If you NOW click&drag again in the left list, you will experience BRUTAL slowdown.n" +
                    "n" +
                    "Once Swing has calmed down, click any entry EXCEPT the first entry of the right list.n" +
                    "Click&drag again in the left list - the problem is gone.n" +
                    "n" +
                    "The built-in workaround (off by default) simulates this.";
            JOptionPane.showMessageDialog(window,
                                          msg,
                                          "How to reproduce the Swing bug:",
                                          JOptionPane.INFORMATION_MESSAGE);

        });
    }

    final private static Random RAND = new Random(0);

    final private static Map<String, List<String>> DATA = createDataMap();

    private static Map<String, List<String>> createDataMap() {
        final Map<String, List<String>> ret = new HashMap<>();
        for (int i = 0; i < 30; i++) {

            final int listSize = 20 + RAND.nextInt(5000);

            final String key = generateRandomString('A');
            final List<String> value = new ArrayList<>(listSize);
            ret.put(key, value);

            for (int ii = 0; ii < listSize; ii++) {
                value.add(generateRandomString('a'));
            }
        }
        return ret;
    }

    private static String generateRandomString(final char baseChar) {
        final StringBuilder sb = new StringBuilder();
        final int len = 4 + RAND.nextInt(17);
        for (int i = 0; i < len; i++) {
            sb.append((char) (baseChar + RAND.nextInt(26)));
        }
        return sb.toString();
    }

}

(标题编辑：删除＆quot，绝对是Java错误＆quot＆quot＆quot＆quot

问题在某种程度上是值列表的原型单元格值，因为我现在将解决方案缩减为一行：设置此值：

valueList.setPrototypeCellValue("                ");

再次，我不知道为什么会起作用，但是问题必须驻留在这里，因为这解决了一切。也许这与列表如何与JSCrollpane进行交互有关，因为原型单元格值是计算可滚动视口大小和首选大小的关键。

我还不知道问题的根源(因此，这是作为"社区Wiki"的回答，而不是个人答案(，但是如果您的问题消失了，则该问题消失了设置Jlist的可见行计数和原型单元格值(这是秋千最佳实践(。

请注意，在更改模型之前删除值列表的选择侦听器，然后在更改模型后重新添加它们，这无助于您的问题。我的直觉是这是一个渲染和尺寸的问题。

工作代码：

import javax.swing.*;
import java.awt.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Random;
final public class Foo {
    public static void main(final String[] args) {
        SwingUtilities.invokeLater(() -> {
            final DefaultListModel<String> valueListModel = new DefaultListModel<>();
            final JList<String> valueList = new JList<>(valueListModel);
            final DefaultListModel<String> keyListModel = new DefaultListModel<>();
            for (String key : Foo.DATA.keySet()) {
                keyListModel.addElement(key);
            }
            final JList<String> keyList = new JList<>(keyListModel);
            keyList.addListSelectionListener(e -> {
                if (e.getValueIsAdjusting()) {
                    valueListModel.clear();
                    final String key = keyList.getSelectedValue();
                    if (key != null) {
                        for (String value : Foo.DATA.get(key)) {
                            valueListModel.addElement(value);
                        }
                    }
                }
            });
            keyList.setVisibleRowCount(25);
            valueList.setVisibleRowCount(25);
            String prototypeFormat = "%100s";
            keyList.setPrototypeCellValue(String.format(prototypeFormat, " "));
            valueList.setPrototypeCellValue(String.format(prototypeFormat, " "));
            final JPanel contentPane = new JPanel(new GridLayout(1, 0, 0, 0));
            contentPane.add(new JScrollPane(keyList));
            contentPane.add(new JScrollPane(valueList));
            final JFrame window = new JFrame();
            window.setContentPane(contentPane);
            window.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
            // window.setMinimumSize(new Dimension(1200, 1000));
            window.pack();
            window.setLocationRelativeTo(null);
            window.setVisible(true);
        });
    }
    final private static Random RAND = new Random(0);
    final private static Map<String, List<String>> DATA = createDataMap();
    private static Map<String, List<String>> createDataMap() {
        final Map<String, List<String>> ret = new HashMap<>();
        for (int i = 0; i < 30; i++) {
            final int listSize = 20 + RAND.nextInt(5000);
            final String key = generateRandomString('A');
            final List<String> value = new ArrayList<>(listSize);
            ret.put(key, value);
            for (int ii = 0; ii < listSize; ii++) {
                value.add(generateRandomString('a'));
            }
        }
        return ret;
    }
    private static String generateRandomString(final char baseChar) {
        final StringBuilder sb = new StringBuilder();
        final int len = 4 + RAND.nextInt(17);
        for (int i = 0; i < len; i++) {
            sb.append((char) (baseChar + RAND.nextInt(26)));
        }
        return sb.toString();
    }
}

每次执行此操作：

valueListModel.addElement(value);

您正在制作正确的jlist重新绘制本身。做很多次是您放缓的原因。

您需要一次更改整个模型。更换此：

final String key = keyList.getSelectedValue();
if (key != null) {
    for (String value : Main.DATA.get(key)) {
        valueListModel.addElement(value);
    }
}

与此：

final String key = keyList.getSelectedValue();
if (key != null) {
    valueListModel.addAll(Main.DATA.get(key));
}

这使模型将一个listDataevent发送给JLIST，而不是每个元素的事件，因此Jlist仅重新绘制一次。

更新：

在Java 8中，您想通过简单地创建一个新的listmodel来实现相同的"设置整个模型"效果。更换此：

valueListModel.clear();
final String key = keyList.getSelectedValue();
if (key != null) {
    for (String value : Main.DATA.get(key)) {
        valueListModel.addElement(value);
    }
}

与此：

DefaultListModel<String> newListModel = new DefaultListModel<>();
final String key = keyList.getSelectedValue();
if (key != null) {
    for (String value : JListSlowDown.DATA.get(key)) {
        newListModel.addElement(value);
    }
}
valueList.setModel(newListModel);