简单的画图工具

  简易画板主要使用JFrame，JPanel，JLabel等，还要添加相应的监听器。
    首先新建主类。
     JFrame是一个容器，允许程序员把其他组件添加到它里面，把它们组织起来，并把它们呈现给用户。
    

public static void main(String[] args) {
		DrawUI ui = new DrawUI();
		ui.initDrawUI();
	}
	
	public void initDrawUI() 
	{
		this.setTitle("画板");
		this.setSize(600,500);
		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                                this.setVisible(ture);
                }
      }

      将整个窗口分为西边，南边和中间三面，西边放工具，南边放颜色挑选，中间放置画板。所以整个窗口需要BorderLayout来分割窗口。

       BorderLayout一个布置容器的边框布局，它可以对容器组件进行安排，并调整其大小，使其符合下列五个区域：北、南、东、西、中。每个区域最多只能包含一个组件，并通过相应的常量进行标识：NORTH、SOUTH、EAST、WEST、CENTER。当使用边框布局将一个组件添加到容器中时，要使用这五个常量之一。

     

      //添加BorderLayout方法分割窗口：
      BorderLayout layout = new BorderLayout();
      this.setLayout(layout);

      //分别在三面添加JPanel类，划分大小，并分别设置西边南边和中间的背景颜色。
      JPanel left = new JPanel();
      left.setPreferredSize(new Dimension(80,1));
      left.setBackground(new Color(235,235,235));
      
      JPanel center = new JPanel();
      center.setBackground(Color.GRAY);
      
      JPanel foot = new JPanel();
      foot.setPreferredSize(new Dimension(1,80));
      foot.setBackground(new Color(235,235,235));

      //添加到窗口上
      this.add(left,BorderLayout.WEST);
      this.add(center,BorderLayout.CENTER);
      this.add(foot,BorderLayout.SOUTH);

    //在left添加工具按钮，并添加触碰，按下等的动作变化（这里需要用到for函数）。
      //由于是单选按钮，则需要填加到group中。
      ButtonGroup group = new ButtonGroup();
      String[] commands = {"0","1","eraser","3","4","5","pencil","7","喷枪","9","line","11",
        		"rect","13","oval","15"
        };
      for(int i=0;i<16;i++)
        {
        	JRadioButton radio = new JRadioButton();
        	ImageIcon lineIcon = new ImageIcon("imgs/draw"+i+".jpg");
        	radio.setIcon(lineIcon);
          
            ImageIcon lineIcon1 = new ImageIcon("imgs/draw"+i+"-1.jpg");
            radio.setRolloverIcon(lineIcon1);
          
            ImageIcon lineIcon2 = new ImageIcon("imgs/draw"+i+"-2.jpg");
            radio.setPressedIcon(lineIcon2);
          
            ImageIcon lineIcon3 = new ImageIcon("imgs/draw"+i+"-3.jpg");
            radio.setSelectedIcon(lineIcon3);
            
            radio.setActionCommand(commands[i]);
            
            group.add(radio);
            
            left.add(radio);

        }  
        //设置默认选择为pencil
        if(i==6)
            {
            	radio.setSelected(true);
            }
         
        //为center添加画板。
        //JPanel 是一般轻量级容器。可以无限重叠自身。
        JPanel drawPanel= new MyPanel();
		drawPanel.setBackground(Color.WHITE);
		drawPanel.setPreferredSize(new Dimension(400,300));
        Graphics g = drawPanel.getGraphics();

    //为工具添加鼠标监听器,将group和画板传入监听器，由此在选择group时     
    //对Graphics进行操作。
         DrawListener dlis = new DrawListener(g,group);
		
         drawPanel.addMouseListener(dlis);
		
         drawPanel.addMouseMotionListener(dlis);
        //新建DrawListener类
        public class DrawListener implements MouseListener,MouseMotionListener{
	
	private int x1,x2,y1,y2;
	private String type="line";
	private Graphics g;
	private ButtonGroup group;
        public DrawListener(Graphics g,ButtonGroup group)
	{
                                this.g = g; 
		this.group = group;
	}
        }
        //实现相应函数。
        public void mousePressed(MouseEvent e)
	    {
	    	// 鼠标按下的时候需要知道要绘制的形状是什么
	    	
	    	javax.swing.ButtonModel bm = group.getSelection();
	    	
	    	String command=bm.getActionCommand();
	    	
	    	type=command;
	    	
	    	g = drawPanel.getGraphics();
	    	c = clis.color;
	    	
	    	x1=e.getX();
	    	y1=e.getY();
	    }
	    public void mouseReleased(MouseEvent e)
	    {
	    	x2=e.getX();
	    	y2=e.getY();
	    	
	    	if(type.equals("line"))
	    	{
	    		g.drawLine(x1,y1,x2,y2);
	    	}
	    	else if(type.equals("rect"))
	    	{
	    		int minX = x1<x2?x1:x2;
	    		int minY = y1<y2?y1:y2;
	    		int width = x1<x2?x2-x1:x1-x2;
	    		int height = y1<y2?y2-y1:y1-y2;
	    		
	    		g.drawRect(minX, minY, width, height );
	    	}
	    	else if(type.equals("oval"))
	    	{
	    		int minX = Math.min(x1, x2);
	    		int minY = Math.min(y1, y2);
	    		int width = Math.abs(x2-x1);
	    		int height = Math.abs(y2-y1);
	    		g.drawOval(minX, minY, width, height );
	    	}
	    	else if(type.equals("eraser"))
	    	{
	    		int lx = e.getX();
	    		int ly = e.getY();
	    		int width = 10;
	    		int height = 10;
                                                g.setColor(Color.WHITE);
	    		g.fillRect(lx, ly, width, height);
	    		x1 = lx;
	    		y1 = ly;
	    		g.setColor(Color.BLACK);
	    	}
	    	else if (type.equals("喷枪")) 
	    	{
	    	      
	    	      int x1 = e.getX();
	    	      int y1 = e.getY();
	    	      for(int i=0;i<100;i++)
	    	      {
	    	    	  int x2 = 15- (int) (Math.random()*30);
	    	          int y2 = 15- (int) (Math.random()*30);
	    	      
	    	          g.drawLine(x1+x2, y1+y2, x1+x2, y1+y2);
	    	      }
	    	      
	    	}
	    }

		public void mouseDragged(MouseEvent e) {
			if(type.equals("pencil"))
			{
				int x3 = e.getX();
				int y3 = e.getY();
				
				g.drawLine(x1, y1, x3, y3);
				x1 = x3;
				y1 = y3;
			}

	    	else if(type.equals("eraser"))
	    	{
	    		int lx = e.getX();
	    		int ly = e.getY();
	    		int width = 10;
	    		int height = 10;
	    		g.setColor(Color.WHITE);
	    		g.fillRect(lx, ly, width, height);
	    		x1 = lx;
	    		y1 = ly;
	    		g.setColor(Color.BLACK);
	    	}
	    	else if (type.equals("喷枪")) 
	    	{
	    	      
	    	      int x1 = e.getX();
	    	      int y1 = e.getY();
	    	      for(int i=1;i<50;i++)
	    	      {
	    	    	  int x2 = 15- (int) (Math.random()*30);
	    	          int y2 = 15- (int) (Math.random()*30);
	    	      
	    	          g.drawLine(x1+x2, y1+y2, x1+x2, y2+y1);
	    	      }
	    	      
	    	}

			
		}



	    public void mouseEntered(MouseEvent e)
	    {
	    	
	    }
	    public void mouseExited(MouseEvent e)
	    {
	    	
	    }
	    public void mouseClicked(MouseEvent e)
	    {
		 
	    }

		@Override
	    public void mouseMoved(MouseEvent e) {
			// TODO Auto-generated method stub
			
	    }

               
        保存绘画数据，且绘画始终在画板上。
        将DrawUI中的drawPanel传入DrawListener中，则改为：
        DrawListener dlis = new DrawListener(drawPanel,group);
        DrawListener的构造函数更改：
        public DrawListener(JPanel drawPanel,ButtonGroup group)
{
this.drawPanel = drawPanel;
this.group = group;
}
        添加private JPanel drawPanel;
       
        添加数组，存储数据：
        定义一个shape类，然后让类Line继承，这样就可以将line的对象存储到数组中
       

public abstract class Shape {
	int x1,y1,x2,y2;
	Color color;
	
	public abstract void draw(Graphics g);
	
        }
        public class Line extends Shape{
	int x1,y1,x2,y2;
	Color color;
	Graphics group;
	public Line(int x1,int y1,int x2,int y2,Color color)
	{
		this.x1 = x1;
		this.x2 = x2;
		this.y1 = y1;
		this.y2 = y2;
		this.color = color;
		
	}
	@Override
	public void draw(Graphics g) {
		g.setColor(this.color);
		g.drawLine(x1, y1, x2, y2);
		
	}

	
	
        }

         
       
        类似Line类可以写出相应的Oval类，Rect类等。  
       
        在DrawListener中的绘画直线的函数就更改为：
        Line line = new Line(x1,y1,x2,y2,color.BLACK);
        line.draw(g);
        用MyPanel类重写JPanel类中的paint方法，使得每次更改窗口都会重绘存储在数组中的数据。
       

        class MyPanel extends JPanel
	{

		@Override
		public void paint(Graphics g) {
			super.paint(g);
			for(int i=0;i<DrawListener.shapeList.size();i++)
			{
				Shape s = DrawListener.shapeList.get(i);
				s.draw(g);
			}
		}

		
	}

        JPanel drawPanel = new JPanel();更改为JPanel drawPanel = new MyPanel();
        DrawListener中添加：
        public static ArrayList<Shape> shapeList = new ArrayList<Shape>();
        绘制line中添加
        shapeList.add(line);
       
        为颜色按钮添加ColorListener监听器
        public class ColorListener extends MouseAdapter implements ActionListener{
@Override
public void mouseReleased(MouseEvent e) {
super.mouseReleased(e);
JLabel label = (JLabel) e.getSource();

color = label.getBackground();
}


Color color;

@Override
public void actionPerformed(ActionEvent e) {
color = JColorChooser.showDialog(null, "请选择颜色", Color.RED);

}


        }
     
        在DrawUI中实现
        在foot中添加颜色按钮
        for(int i=0;i<colors.length;i++){
JLabel label = new JLabel();

    label.setPreferredSize(new Dimension(34,29));
label.setBackground(colors[i]);
//前景色是否透明
label.setOpaque(true);

foot.add(label);
label.addMouseListener(clis);
}
      
        颜色监听器放在工具监听器的前面，将颜色监听器的对象传入工具监听器中，实现对绘画的改色。
        DrawListener dlis = new DrawListener(drawPanel,group,clis);
        相应的构造函数需要改变。
        public DrawListener(JPanel drawPanel,ButtonGroup group,ColorListener clis)
{
this.drawPanel = drawPanel;
this.group = group;
this.clis = clis;
}
        在foot中添加颜色选择器（传入照片color.png)
        JButton btn = new JButton();
ImageIcon icon = new ImageIcon("color.png");
btn.setIcon(icon);
btn.setPreferredSize(new Dimension(34,29));
foot.add(btn);

btn.addActionListener(clis);