Java实现画图板

运行后可以效果如下：
功能：

 1.可进行三角形，圆形的相应图形进行绘制
 2.可设置绘制图形的颜色
 3.可显示当前绘制图形的周长，面积等信息
 4.将绘制好的图片保存到本地

进行相应画图截图：
用到的知识：

1.反射解耦
2.接口多态
3.继承封装
4.其他Java基础知识

部分代码：

public class PaintApp {

	public static void main(String[] args) {

		try {
			UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
		} catch (ClassNotFoundException | InstantiationException | IllegalAccessException
				| UnsupportedLookAndFeelException e) {
			e.printStackTrace();
		}

		JFrame frame = new JFrame("画图板");
		frame.setSize(500, 500);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setLayout(new BorderLayout());

		MyCanvas canvas = new MyCanvas();
		canvas.setBackground(Color.white);
		frame.add(canvas, BorderLayout.CENTER);
		JMenuBar menuBar = new JMenuBar();

		JButton rectBtn = new JButton(new ImageIcon("D:\\java\\Exp_PaintBord_chenhao\\resource\\rect.png"));
		rectBtn.addActionListener(new ActionListener() {

			@Override
			public void actionPerformed(ActionEvent e) {
				canvas.setFigType("rectangle");

			}
		});
		menuBar.add(rectBtn);

		JButton lineBtn = new JButton(new ImageIcon("D:\\java\\Exp_PaintBord_chenhao\\resource\\line.png"));
		lineBtn.addActionListener(new ActionListener() {

			@Override
			public void actionPerformed(ActionEvent e) {
				canvas.setFigType("line");

			}
		});

		menuBar.add(lineBtn);

		JButton ellipseBtn = new JButton(new ImageIcon("D:\\java\\Exp_PaintBord_chenhao\\resource\\ellipse.png"));
		ellipseBtn.addActionListener(new ActionListener() {

			@Override
			public void actionPerformed(ActionEvent e) {
				canvas.setFigType("ellipse");

			}
		});
		menuBar.add(ellipseBtn);

		JButton eqTriangleBtn = new JButton(new ImageIcon("D:\\java\\Exp_PaintBord_chenhao\\resource\\eqTriangle.png"));
		eqTriangleBtn.addActionListener(new ActionListener() {

			@Override
			public void actionPerformed(ActionEvent e) {
				canvas.setFigType("eqTriangle");

			}
		});
		menuBar.add(eqTriangleBtn);

		JButton rightTriangleBtn = new JButton(
				new ImageIcon("D:\\java\\Exp_PaintBord_chenhao\\resource\\rightTriangle.png"));
		rightTriangleBtn.addActionListener(new ActionListener() {

			@Override
			public void actionPerformed(ActionEvent e) {
				canvas.setFigType("rightTriangle");

			}
		});
		menuBar.add(rightTriangleBtn);

		JButton colorBtn = new JButton("■");
		colorBtn.setForeground(Color.black);
		colorBtn.addActionListener(new ActionListener() {

			@Override
			public void actionPerformed(ActionEvent e) {
				Color color = JColorChooser.showDialog(frame, "绘制颜色", colorBtn.getForeground());
				colorBtn.setForeground(color);
				canvas.setColor(color);
			}
		});
		menuBar.add(colorBtn);

		JButton saveBtn = new JButton("保存");

		saveBtn.addActionListener(new ActionListener() {

			@Override
			public void actionPerformed(ActionEvent e) {
				JFileChooser chooser = new JFileChooser();
				if(chooser.showSaveDialog(frame) == JFileChooser.APPROVE_OPTION) {
					File file = chooser.getSelectedFile();
					try {
						canvas.savePic(file);
					} catch (IOException e1) {
						// TODO Auto-generated catch block
						e1.printStackTrace();
					}
				}
				
;				
			}
		});
		menuBar.add(saveBtn);

		frame.add(menuBar, BorderLayout.NORTH);

		frame.setVisible(true);

	}

}


```java
public class MyCanvas extends Canvas {
	
	static Properties config ;

	static {
		try {
			config = new Properties();
			config.load(MyCanvas.class.getResourceAsStream("config.properties"));
		} catch (IOException e) {
			
			e.printStackTrace();
		}
	}
	private Figure figure;

	private String figType = "line";
	
	private Color color = Color.black;

	List<Figure> figures = new ArrayList<>();

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

	public void setFigType(String figType) {
		this.figType = figType;
	}

	MouseAdapter adapter = new MouseAdapter() {

		@Override
		public void mousePressed(MouseEvent e) {
			
			try {
				Class clz = Class.forName(config.getProperty(figType));
				Constructor constructor = clz.getConstructor();
				figure = (Figure)constructor.newInstance();
			} catch (ClassNotFoundException | NoSuchMethodException | SecurityException | InstantiationException
					| IllegalAccessException | IllegalArgumentException | InvocationTargetException e1) {
				
				e1.printStackTrace();
			}
			
			
            figure.setColor(color);
			figure.setStart(e.getPoint());

		}

		@Override
		public void mouseReleased(MouseEvent e) {

			figures.add(figure);
		}

		@Override
		public void mouseDragged(MouseEvent e) {

			figure.setEnd(e.getPoint());
			MyCanvas.this.repaint();
		}

	};

	public MyCanvas() {
		this.addMouseListener(adapter);
		this.addMouseMotionListener(adapter);
	}

	@Override
	public void paint(Graphics g) {

		super.paint(g);
		g.setColor(Color.white);
		g.fillRect(0, 0, getWidth(), getHeight());
		for (Figure figure : figures) {
			figure.draw(g);
		}
		if (figure != null) {
			figure.draw(g);
			Point strat = figure.getStart();
			Point end = figure.getEnd();
			StringBuilder sb = new StringBuilder();
			sb.append("起点:("+strat.x+","+strat.y+")");
			sb.append("|终点:("+end.x+","+end.y+")");
			
			if(figure instanceof Lengthable) {
				Lengthable lengthable = (Lengthable)figure;
				sb.append("|长度:"+lengthable.length());
			}
			if(figure instanceof Areable) {
				Areable area = (Areable)figure;
				sb.append("|面积:"+area.area());
			}
			if(figure instanceof Perimeterable) {
				Perimeterable pe = (Perimeterable)figure;
				sb.append("|周长:"+pe.perimeter());
			}
			
			
			g.drawString(sb.toString(), 20, getHeight()-20);
			
			
		}

		
	}
	
	public void savePic(File file) throws IOException {
		BufferedImage image = new BufferedImage(this.getWidth(), this.getHeight(), BufferedImage.TYPE_INT_BGR);
		
		Graphics g = image.createGraphics();
		
		this.paint(g);
		g.dispose();
		//File file = new File(pathName);
		
		if(!file.exists()) {
			file.createNewFile();
		}
		ImageIO.write(image, "jpg", file);
		
	}

}

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