画图板

1、画图工具：

Graphics

需要在哪个组件上绘图，哪个组件就获取Graphics

例如：窗体组件获取Graphics

//添加监听器：

DrawListener DrawL=new DrawListener();

frame.addMouseListener(DrawL);

frame.setVisible(true);

//以下部分要写在Visible下面

Graphics g=frame.getGraphics();

DrawL.setG(g);

System.out.println("g");

2、创建监听器：

public class DrawListener implements MouseListener{

int x1,x2,y1,y2;
Graphics g;

public void setG(Graphics g){
this.g=g;
}
public void mouseClicked(MouseEvent e){
System.out.println("点击");
}

public void mousePressed(MouseEvent e){

x1=e.getX();
y1=e.getY();

public void mouseReleased(MouseEvent e){

x2=e.getX();
y2=e.getY();

g.setColor(Color.blue);
g.fillRect(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2-x1),Math.abs(y2-y1));       坐标：（0,0）向右x增大，向下y增大
g.setColor(Color.YELLOW);
g.fillOval(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2-x1), Math.abs(y2-y1));
g.setColor(Color.red);
g.drawLine(x1, y1, x2, y2);
g.drawLine(x1, y2, x2, y1);
g.drawLine((x1+x2)/2, y1, (x1+x2)/2, y2);
g.drawLine(x1, (y1+y2)/2, x2,(y1+y2)/2 );

}

public void mouseEntered(MouseEvent e){
System.out.println("进入");
}

public void mouseExited(MouseEvent e){
System.out.println("离开");
}

}