Java Swing的基础

首先需要注意的就是JFrame这个类，如果在main类整直接new一个出来是没有任何的变化，需要设置一个setvisible为true来显示出来。

public class AlgorFrame extends JFrame {
    private int canvasWith;
    private int canvasHeight;

    public AlgorFrame(String title, int cancasWidth, int canvasHeight) {
        super(title);
        this.canvasHeight = canvasHeight;
        this.canvasWith = cancasWidth;
        this.setSize(cancasWidth, canvasHeight);
        this.setResizable(false);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
    }

这是一个标准的模板，设置窗口大小不可重新改变，关闭窗口时整个程序同时关闭。

JFrame是最上层的一个窗口，如果要绘制的话是不可以在窗口本身绘制的。MenuBar就是最大化最小化关闭等等的操作。Content Pane其实是一个容器，可以装载其他的组件，最常用的就是面板，Jpanel就是一个面板，后面的绘制都会画在Jpanel上。也就是说想要画上东西就需要在Jframe上加入Jpanel。这个时候窗口大小和画布大小就是两个不一样的大小了，如果想要窗口大小自适应画布大小，就可以调用pack这个函数自适应。

绘制

在Jpanel类里面有一个paintComponent方法，这个方法是自带的一个方法，需要绘制的操作都要在这里面画。paintComponent带了一个画笔参数。

    private class AlgoCanvas extends JPanel {
        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.drawOval(50, 50, 300, 300);
        }
    }

画一个简单的圆。

但其实如果是仅仅在2D图像上画其实可以使用Graphic2D来画，把Graphic转换成Graphic2D就好了，而paintComponent是没有2D的这个参数的。这个时候画法就不一样了。

    private class AlgoCanvas extends JPanel {
        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D graphics2D = (Graphics2D)g;
            Ellipse2D cirle = new Ellipse2D.Float(50, 50, 300, 300);
            graphics2D.draw(cirle);
            //g.drawOval(50, 50, 300, 300);
        }
    }

如果想要设置颜色，就可以直接调用setColor即可，而这个条件会一直持续要后面结束为止。

抗锯齿

可以看到上面画出的图片有点锯齿边界，不好看。之所以有抗锯齿是因为我们总是把一个像素是非黑即白，抗锯齿就很简单了，利用边缘的透明度灰度就好了，这样在视觉上看就会平滑一些。

双缓存

这种技术表现在动画上。首先看一下单缓存，比如要在画布上画上一个圆，现在要挪动这个圆的位置，那么就必须把这个画布上的圆抹掉，然后再新的位置画上。在我们视觉上就会看到闪烁了一下，有一个经典的解决方法，就是用双缓存，也就是两个画布，用画布的切换来演示动画的运行。要开启其实很简单：

        public AlgoCanvas(){
            super(true);
        }

简单动画

       EventQueue.invokeLater(() -> {
            AlgorFrame algorFrame = new AlgorFrame("Welcome", 500, 500);
            new Thread(() -> {
                while (true) {
                    algorFrame.render(circles);
                    try {
                        Thread.sleep(20);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    for (Circle circle : circles) {
                        circle.move();
                    }
                }
            }).start();
        });
    }
}

MVC

用一个弹球动画演示。首先Frame层就是一个view试图层，小球类就是属于model数据层，还差一个控制层把两个逻辑连接起来。

public class AlgoVisualizer {
    private Circle[] circles;
    private AlgorFrame algorFrame;

    public AlgoVisualizer(int sceneWidth, int sceneHeight, int n) {
        circles = new Circle[n];
        for (int i = 0; i < n; i++) {
            Circle circle = new Circle(30, 30, 5, new Random().nextInt(5), new Random().nextInt(5));
            circles[i] = circle;
        }
        EventQueue.invokeLater(() -> {
            algorFrame = new AlgorFrame("Welcome", 500, 500);
            new Thread(() -> {
                run();
            }).start();
        });
    }

    private void run() {
        while (true) {
            algorFrame.render(circles);
            try {
                Thread.sleep(20);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            for (Circle circle : circles) {
                circle.move(0, 0, algorFrame.getCanvasWith(), algorFrame.getCanvasHeight());
            }
        }
    }
}

这个就作为控制类。在后面写算法的时候，可视化的操作就可以放在run方法里面写了。

交互

现在添加一个暂停功能。实现键盘监听有两个方法，第一个就是实现接口KeyListener，第二个就是继承KeyAdapter，KeyAdapter其实就是实现了刚刚的那个接口而已，只不过是空方法而已。

private class AlgoKeyListener extends KeyAdapter {
        @Override
        public void keyReleased(KeyEvent e) {
            if (e.getKeyChar() == ' ') {
                isAnimated = !isAnimated;
            }
        }
    }

鼠标也是一样的，写好监听器，然后注册即可。

    private class AlgoMouseListener extends MouseAdapter {
        @Override
        public void mousePressed(MouseEvent event) {
            //System.out.println(event.getPoint());
            event.translatePoint(0, -(algorFrame.getBounds().height - algorFrame.getCanvasHeight()));
            System.out.println(event.getPoint());
        }
    }

简单的界面交互就到这来了。对于上面的实现基本是可以成一个模板的：

package ApplicationOfAlgorithm.Probability;

import javax.swing.*;
import java.awt.*;

public class AlgorithmFrame extends JFrame {
    private int canvasWidth;
    private int canvasHeight;

    public AlgorithmFrame(String title, int canvasWidth, int canvasHeight) {
        super(title);
        this.canvasWidth = canvasWidth;
        this.canvasHeight = canvasHeight;

    }

    private class AlgorithmCanvas extends JPanel {
        public AlgorithmCanvas() {
            super(true);
        }

        @Override
        public void paintComponent(Graphics graphics) {
            super.paintComponent(graphics);
            Graphics2D graphics2D = (Graphics2D) graphics;
            RenderingHints hints = new RenderingHints(
                    RenderingHints.KEY_ANTIALIASING,
                    RenderingHints.VALUE_ANTIALIAS_ON
            );
            hints.put(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY);
            graphics2D.addRenderingHints(hints);
        }

        @Override
        public Dimension getPreferredSize(){
            return new Dimension(canvasWidth, canvasHeight);
        }
    }
}

view层的模板。

package ApplicationOfAlgorithm.Probability;

import java.awt.*;
import java.awt.event.KeyAdapter;
import java.awt.event.MouseAdapter;

public class AlgorithmVisualizer {
    private Object data;
    private AlgorithmFrame frame;

    public AlgorithmVisualizer(int sceneWidth, int sceneHeight) {
        EventQueue.invokeLater(() -> {
            frame = new AlgorithmFrame("title", sceneWidth, sceneHeight);
            frame.addKeyListener(new AlgoKeyListener());
            frame.addMouseListener(new AlgoMouseListener());
            new Thread(() -> {
                run();
            }).start();
        });
    }

    private void run() {

    }

    private class AlgoKeyListener extends KeyAdapter {
    }

    private class AlgoMouseListener extends MouseAdapter {
    }
}

控制层模板。

  package ApplicationOfAlgorithm.Probability;

import javax.swing.*;
import java.awt.*;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Rectangle2D;

public class AlgorithmHelper {
    private AlgorithmHelper() {
    }

    public static final Color Red = new Color(0xF44336);
    public static final Color Pink = new Color(0xE91E63);
    public static final Color Purple = new Color(0x9C27B0);
    public static final Color DeepPurple = new Color(0x673AB7);
    public static final Color Indigo = new Color(0x3F51B5);
    public static final Color Blue = new Color(0x2196F3);
    public static final Color LightBlue = new Color(0x03A9F4);
    public static final Color Cyan = new Color(0x00BCD4);
    public static final Color Teal = new Color(0x009688);
    public static final Color Green = new Color(0x4CAF50);
    public static final Color LightGreen = new Color(0x8BC34A);
    public static final Color Lime = new Color(0xCDDC39);
    public static final Color Yellow = new Color(0xFFEB3B);
    public static final Color Amber = new Color(0xFFC107);
    public static final Color Orange = new Color(0xFF9800);
    public static final Color DeepOrange = new Color(0xFF5722);
    public static final Color Brown = new Color(0x795548);
    public static final Color Grey = new Color(0x9E9E9E);
    public static final Color BlueGrey = new Color(0x607D8B);
    public static final Color Black = new Color(0x000000);
    public static final Color White = new Color(0xFFFFFF);

    public static void strokeCircle(Graphics2D graphics2D, int x, int y, int r) {
        Ellipse2D circle = new Ellipse2D.Double(x - r, y - r, 2 * r, 2 * r);
        graphics2D.draw(circle);
    }

    public static void fillCircle(Graphics2D graphics2D, int x, int y, int r) {
        Ellipse2D circle = new Ellipse2D.Double(x - r, y - r, 2 * r, 2 * r);
        graphics2D.fill(circle);
    }

    public static void strokeRectangle(Graphics2D g, int x, int y, int w, int h) {

        Rectangle2D rectangle = new Rectangle2D.Double(x, y, w, h);
        g.draw(rectangle);
    }

    public static void fillRectangle(Graphics2D g, int x, int y, int w, int h) {

        Rectangle2D rectangle = new Rectangle2D.Double(x, y, w, h);
        g.fill(rectangle);
    }

    public static void setColor(Graphics2D g, Color color) {
        g.setColor(color);
    }

    public static void setStrokeWidth(Graphics2D g, int w) {
        int strokeWidth = w;
        g.setStroke(new BasicStroke(strokeWidth, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
    }

    public static void pause(int t) {
        try {
            Thread.sleep(t);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void putImage(Graphics2D graphics2D, int x, int y, String imageURL) {
        ImageIcon imageIcon = new ImageIcon(imageURL);
        Image image = imageIcon.getImage();
        graphics2D.drawImage(image, x, y, null);
    }

    public static void drawText(Graphics2D g, String text, int centerx, int centery) {

        if (text == null)
            throw new IllegalArgumentException("Text is null in drawText function!");

        FontMetrics metrics = g.getFontMetrics();
        int w = metrics.stringWidth(text);
        int h = metrics.getDescent();
        g.drawString(text, centerx - w / 2, centery + h);
    }

}

model层的模板。