Java学习笔记 - 第016天

每日要点

工厂

简单工厂模式/静态工厂模式
用工厂创建对象(跟具体的类型实现解耦合)

static

static属于这个类，不属于这个类的任何对象，有且只有一个

给窗口或者窗口上的控件注册事件监听器

给窗口或者窗口上的控件注册事件监听器(绑定事件回调方法)有三种做法:

• 1.创建匿名内部类的对象(就地实例化)
• 2.创建一个内部类对象(因为有名字随时都可以创建对象)
• 3.让窗口实现接口用窗口对象(this)充当监听器

从Java 8开始,对于单方法接口(函数式接口)可以使用Lambda表达式
使用λ表达式其实就是写一个匿名方法来编写事件回调代码

垃圾回收

Java虽然拥有垃圾回收(Garbage Collection)机制
但如果程序编写不当仍然有可能造成内存泄漏
垃圾回收是针对内存堆空间的无用对象清理工作

例子

• 1.绘图工具
  图形抽象类:

/**
 * 图形(抽象类)
 * 
 * @author Kygo
 *
 */
public abstract class Shape {
    protected int startX;       // 起点横坐标
    protected int startY;       // 起点纵坐标
    protected int endX;         // 终点横坐标
    protected int endY;         // 终点纵坐标
    protected Color color;      // 颜色
    protected float lineWidth;  // 粗细
    
    public void draw(Graphics g) {
        g.setColor(color);
        ((Graphics2D) g).setStroke(new BasicStroke(lineWidth));
    }

    public void setStartX(int startX) {
        this.startX = startX;
    }

    public void setStartY(int startY) {
        this.startY = startY;
    }

    public void setEndX(int endX) {
        this.endX = endX;
    }

    public void setEndY(int endY) {
        this.endY = endY;
    }

    public void setColor(Color color) {
        this.color = color;
    }

    public void setLineWidth(float lineWidth) {
        this.lineWidth = lineWidth;
    }
}

直线类:

public class Line extends Shape {

    @Override
    public void draw(Graphics g) {
        super.draw(g);
        g.drawLine(startX, startY, endX, endY);
    }   
}

矩形类:

public class Rect extends Shape {

    @Override
    public void draw(Graphics g) {
        super.draw(g);
        int x = startX < endX ? startX : endX;
        int y = startY < endY ? startY : endY;
        int width = Math.abs(startX - endX);
        int height = Math.abs(startY - endY);
        g.drawRect(x, y, width, height);
    }       
}

圆类:

public class Oval extends Shape {
    
    @Override
    public void draw(Graphics g) {
        super.draw(g);
        int x = startX < endX ? startX : endX;
        int y = startY < endY ? startY : endY;
        int width = Math.abs(startX - endX);
        int height = Math.abs(startY - endY);
        g.drawOval(x, y, width, height);
    }
}

三角形类:

public class Triangle extends Shape {
    
    @Override
    public void draw(Graphics g) {
        super.draw(g);
        int x1 = startX > endX ? startX : endX;
        int y1 = startY > endY ? startY : endY;
        int width = Math.abs(startX - endX);
        int x2 = x1 - width;
        int y2 = y1;
        int x3 = (startX < endX ? startX : endX) + width / 2;
        int y3 = startY < endY ? startY : endY;
//      g.drawLine(x1, y1, x2, y2);
//      g.drawLine(x2, y2, x3, y3);
//      g.drawLine(x3, y3, x1, y1);
        g.drawPolygon(new int[] {x1, x2, x3}, new int[] {y1, y2, y3}, 3);
    }
}

图形工厂类:

/**
 * 图形工厂(简单工厂模式/静态工厂模式)
 * @author Kygo
 *
 */
public class ShapeFactory {

    // static属于这个类，不属于这个类的任何对象，有且只有一个 
    /**
     * 创建图形对象的工厂方法
     * @param shapeType 类型
     * @return 图形对象或null
     */
    public static Shape createShape(String shapeType) {
        Shape currentShape = null;
        switch (shapeType) {
        case "矩形":
            currentShape = new Rect();
            break;
        case "椭圆":
            currentShape = new Oval();
            break;
        case "三角形":
            currentShape = new Triangle();
            break;
        case "线条":
            currentShape = new Line();
            break;
        }
        return currentShape;
    }
}

绘画工具窗口:

public class PaintBrushFrame extends JFrame{
    private BufferedImage image = new BufferedImage(800, 600, 1);
    private Shape[] shapesArray = new Shape[100];
    private int totalShapes = 0;
    private String currentType = "线条";
    private Color defaultColor = Color.BLACK;
    private int defaultLineWidth = 1;
    
    // 内部类 - 内部类可以直接使用外部类的私有成员(属性和方法)
    private class MouseHandler extends MouseAdapter{
        
        @Override
        public void mousePressed(MouseEvent e) {
            if (totalShapes < shapesArray.length) {
                int x = e.getX();
                int y = e.getY();
                // 用工厂创建对象(跟具体的图形类型实现解耦合)
                Shape currentShape = ShapeFactory.createShape(currentType);
                currentShape.setColor(defaultColor);
                currentShape.setLineWidth(defaultLineWidth);
                currentShape.setStartX(x);
                currentShape.setStartY(y);
                currentShape.setEndX(x);
                currentShape.setEndY(y);
                shapesArray[totalShapes++] = currentShape;
            }
        }
        
        @Override
        public void mouseDragged(MouseEvent e) {
            if (totalShapes > 0) {
                int x = e.getX();
                int y = e.getY();
                Shape currentShape = shapesArray[totalShapes - 1];
                currentShape.setEndX(x);
                currentShape.setEndY(y);
                repaint();
            }
        }
    }
    
    public PaintBrushFrame() {
        this.setTitle("我的绘图工具");
        this.setSize(800, 600);
        this.setResizable(false);
        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        
        JPanel buttonPanel = new JPanel();
        this.add(buttonPanel, BorderLayout.SOUTH);
        String[] buttonNames = {"线条", "矩形", "椭圆", "三角形"};
        for (String name : buttonNames) {
            JButton button = new JButton(name);
            button.addActionListener(e -> {
                currentType = e.getActionCommand();
            });
            buttonPanel.add(button);
        }
        
        String[] buttonNames2 = {"选择颜色", "-", "+", "撤销", "清空", "保存"};
        for (String name : buttonNames2) {
            JButton button = new JButton(name);
            button.addActionListener(e -> {
                String command = e.getActionCommand();
                switch (command) {
                case "选择颜色":
                    Color currentColor = JColorChooser.showDialog(PaintBrushFrame.this, "请选择颜色", defaultColor);
                    defaultColor = currentColor != null ? currentColor : defaultColor;
                    break;
                case "-":
                    if (defaultLineWidth > 1) {
                        defaultLineWidth -= 1;
                    }
                    break;
                case "+":
                    if (defaultLineWidth < 10) {
                        defaultLineWidth += 1;
                    }
                    break;
                case "撤销":
                    if (totalShapes > 0) {
                        shapesArray[totalShapes - 1] = null;
                        totalShapes -= 1;
                        repaint();
                    }
                    break;
                case "清空":
                    if (totalShapes > 0) {
                        // Java虽然拥有垃圾回收(Garbage Collection)机制
                        // 但如果程序编写不当仍然有可能造成内存泄漏
                        // 垃圾回收是针对内存堆空间的无用对象清理工作
                        for (int i = 0; i < totalShapes; i++) {
                            shapesArray[i] = null;
                        }
                    }
                    totalShapes = 0;
                    repaint();
                    break;
                case "保存":
                    JFileChooser chooser = new JFileChooser();
                    int choice = chooser.showSaveDialog(PaintBrushFrame.this);
                    if (choice == JFileChooser.APPROVE_OPTION) {
                        BufferedImage newImage = new BufferedImage(800, 600, 1);
                        Graphics graphics = newImage.getGraphics();
                        graphics.setColor(Color.WHITE);
                        graphics.fillRect(0, 0, 800, 600);
                        for (int i = 0; i < totalShapes; i++) {
                            shapesArray[i].draw(graphics);
                        }
                        try {
                            ImageIO.write(newImage, "PNG", chooser.getSelectedFile());
                        } catch (IOException e1) {
                            e1.printStackTrace();
                        }
                    }
                    break;
                }
            });
            buttonPanel.add(button);
        }
        
        // 缺省适配模式
        // 给窗口或者窗口上的控件注册事件监听器(绑定事件回调方法)有三种做法:
        //   - 1.创建匿名内部类的对象(就地实例化)
        //   - 2.创建一个内部类对象(因为有名字随时都可以创建对象)
        //   - 3.让窗口实现接口用窗口对象(this)充当监听器
        // 从Java 8开始,对于单方法接口(函数式接口)可以使用Lambda表达式
        // 使用λ表达式其实就是写一个匿名方法来编写事件回调代码
        // 创建匿名内部类的对象
/*      MouseAdapter adapter = new MouseAdapter() {
            
            @Override
            public void mousePressed(MouseEvent e) {
                if (totalShapes < shapesArray.length) {
                    int x = e.getX();
                    int y = e.getY();
                    //Shape currentShape = new Line();
                    //Shape currentShape = new Rect();
                    //Shape currentShape = new Oval();
                    //Shape currentShape = new Triangle();
                    // 用工厂创建对象(跟具体的图形类型实现解耦合)
                    Shape currentShape = ShapeFactory.createShape(currentType);
                    currentShape.setColor(defaultColor);
                    currentShape.setLineWidth(defaultLineWidth);
                    currentShape.setStartX(x);
                    currentShape.setStartY(y);
                    currentShape.setEndX(x);
                    currentShape.setEndY(y);
                    shapesArray[totalShapes++] = currentShape;
                }
            }
            
            @Override
            public void mouseDragged(MouseEvent e) {
                if (totalShapes > 0) {
                    int x = e.getX();
                    int y = e.getY();
                    Shape currentShape = shapesArray[totalShapes - 1];
                    currentShape.setEndX(x);
                    currentShape.setEndY(y);
                    repaint();
                }
            }
        };*/
        MouseAdapter adapter = new MouseHandler();
        this.addMouseListener(adapter);
        this.addMouseMotionListener(adapter);

    }
    
    @Override
    public void paint(Graphics g) {
        Graphics otherGraphics = image.getGraphics();
        super.paint(otherGraphics);
        for (int i = 0; i < totalShapes; i++) {
            shapesArray[i].draw(otherGraphics);
        }
        g.drawImage(image, 0, 0, null);
    }
    
    public static void main(String[] args) {
        new PaintBrushFrame().setVisible(true);
    }
}

作业:

• 1.用容器(Liste、Set)改造下面的代码

    private ArrayList<Shape> shapes = new ArrayList<Shape>();
            shapes.add(totalShapes++, currentShape);
                Shape currentShape = shapes.get(totalShapes - 1);
                        shapes.remove(totalShapes - 1);
                        shapes.clear();
                        for (Shape shape : shapes) {
                            shape.draw(graphics);
                        }
        for (Shape shape : shapes) {
            shape.draw(otherGraphics);
        }

• 2.六角形

public class Hexagon extends Shape {

    @Override
    public void draw(Graphics g) {
        super.draw(g);
        int x = startX > endX ? startX : endX;
        int y = startY > endY ? startY : endY;
        int width = Math.abs(startX - endX);
        int height = Math.abs(startY - endY);
            
        int x1 = x - width / 2;
        int y1 = y - height;
        int x2 = x;
        int y2 = y - 3 * height / 4;
        int x3 = x - width;
        int y3 = y - height / 4;
        int x4 = x - width / 2;
        int y4 = y;
        int x5 = x;
        int y5 = y - height / 4;
        int x6 = x - width;
        int y6 = y - 3 * height / 4;
        
        g.drawPolygon(new int[] {x1, x6, x3, x4, x5, x2}, 
                new int[] {y1, y2, y3, y4, y5,y6}, 6);
    }
}