java - 绘制选择排序的视觉效果

Question

我正在编写一个程序，该程序创建一个包含 50 个数字的数组，然后将它们在面板中绘制为矩形，大小基于数字。单击该面板时，将对数组进行排序，并重新绘制面板以显示正在排序的数字的动画。这是单击面板之前和之后的样子:

这是我的代码:

public class AnimatedSelectionSortPanel extends javax.swing.JPanel {

int[] numbers = new int[50];
int min = 20;
int max = 100;

private void loadArray() {
    int num;
    for (int i = 0; i < numbers.length; i++) {
        numbers[i] = min + (int) Math.random() * ((max - min) + 1);
    }
}

public static void selectionSort(int[] x) {
    for (int i = 0; i < x.length - 1; i++) {
        int minIndex = i;      // Index of smallest remaining value.
        for (int j = i + 1; j < x.length; j++) {
            if (x[minIndex] > x[j]) {
                minIndex = j;  // Remember index of new minimum
            }
        }
        if (minIndex != i) {
            //...  Exchange current element with smallest remaining.
            int temp = x[i];
            x[i] = x[minIndex];
            x[minIndex] = temp;
        }
    }
}

private void drawPass(Graphics g) {
    int xPos = 10;
    int yPos = 120;
    int rectWidth = 1;

    for (int num : numbers) {
        g.setColor(Color.black);
        g.drawRect(xPos, yPos, rectWidth, num);
        xPos += 11;
    }
}

@Override
public void paintComponent (Graphics g) {
    while (numbers.length == 0) {
        loadArray();
    }
    drawPass(g);
}

private void sortPanelMouseClicked(java.awt.event.MouseEvent evt) {
    selectionSort(numbers);
    sortPanel.repaint();
}

我遇到的问题是，当我单击面板时，框架中没有绘制任何内容。有人可以告诉我我所做的事情有什么问题吗？

这里是 GUI 构建器自动生成的代码(如果有帮助的话):

    private void initComponents() {

    sortPanel = new javax.swing.JPanel();

    sortPanel.setBorder(javax.swing.BorderFactory.createLineBorder(new java.awt.Color(0, 0, 0)));
    sortPanel.addMouseListener(new java.awt.event.MouseAdapter() {
        public void mouseClicked(java.awt.event.MouseEvent evt) {
            sortPanelMouseClicked(evt);
        }
    });

    javax.swing.GroupLayout sortPanelLayout = new javax.swing.GroupLayout(sortPanel);
    sortPanel.setLayout(sortPanelLayout);
    sortPanelLayout.setHorizontalGroup(
        sortPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 398, Short.MAX_VALUE)
    );
    sortPanelLayout.setVerticalGroup(
        sortPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 165, Short.MAX_VALUE)
    );

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
    this.setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addComponent(sortPanel, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addComponent(sortPanel, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
    );
}// </editor-fold>

Answer 1

以下是一些建议:

1. 请发布一个可编译的示例 - SSCCE

2. 不要在 paintComponent 中放入太多逻辑，也不要在此方法中分配数据。其目的是绘画。提前准备好数字数组。

3. min + (int) Math.random() * ((max - min) + 1); 始终为 20，因为 (int) Math.random() 始终为零。您应该转换结果，即: min + (int) (Math.random() * ((max - min) + 1));

4. 将排序过程包装到线程或计时器中。在迭代之间等待并调用 repaint() 来绘制中间结果。包装到 Swing 计时器中更干净、更可取，但在发布的代码中，将 selectionSort 的整个逻辑转储到线程中可能会更容易/更快。请参阅Performing Custom Painting教程中的一些示例。另请参阅How to Use Swing Timers 。

5. 看起来 drawPass 绘制了颠倒的矩形。

下面是一个使用现有代码并进行最小更改的示例:

import java.awt.*;
import java.awt.event.*;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class AnimatedSelectionSortPanel extends javax.swing.JPanel {

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

            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new AnimatedSelectionSortPanel());
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.pack();
                frame.setLocationByPlatform(true);
                frame.setVisible(true);
            }
        });
    }


    private int[] numbers = new int[50];
    private int min = 20;
    private int max = 100;
    private boolean shuffle = false;
    public static final int ITERATION_SLEEP = 100;

    public AnimatedSelectionSortPanel() {
        loadArray();
        addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                if (shuffle)
                    loadArray();
                selectionSort(numbers);
                shuffle = true;
            }
        });
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(300, 100);
    }

    private void loadArray() {
        for (int i = 0; i < numbers.length; i++) {
            numbers[i] = min + (int) (Math.random() * ((max - min) + 1));
        }
    }

    public void selectionSort(final int[] x) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                    for (int i = 0; i < x.length - 1; i++) {
                    int minIndex = i; // Index of smallest remaining value.
                    for (int j = i + 1; j < x.length; j++) {
                        if (x[minIndex] > x[j]) {
                            minIndex = j; // Remember index of new minimum
                        }
                    }
                    if (minIndex != i) {
                        // ... Exchange current element with smallest remaining.
                        int temp = x[i];
                        x[i] = x[minIndex];
                        x[minIndex] = temp;
                    }
                    repaint();
                    try {
                        Thread.sleep(ITERATION_SLEEP);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }               
            }
        }).start();
    }

    private void drawPass(Graphics g) {
        int rectWidth = 1;

        int width = getWidth() - 1;
        int height = getHeight() - 1;
        int colSpan = Math.round((float)width / (float)numbers.length);
        int x = 0;

        for (int num : numbers) {
            int colHeight = (int) ((float) height * ((float) num / (float) 100));
            g.fillRect(x, height - colHeight, rectWidth, colHeight);
             x += colSpan;
        }
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        drawPass(g);
    }
}