JAVA中画的图形不能显示，想知道问题出在哪？

Question

package ObjectPrinciple;

import java.awt.EventQueue;

import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JToolBar;
import java.awt.BorderLayout;
import java.awt.Button;

import javax.swing.JPanel;
import javax.swing.JRadioButton;
import java.awt.event.ItemListener;
import java.awt.event.ItemEvent;
import javax.swing.JPanel;
import javax.swing.JSplitPane;
import javax.swing.JList;

public class DrawingBroad implements ItemListener{

private JFrame frame;
private Canvas canvas;
/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                DrawingBroad window = new DrawingBroad();
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}


    public void itemStateChanged(ItemEvent e) {
        JRadioButton rdb;
        rdb=(JRadioButton) e.getSource();//把获得的来源转换成单选按钮的类型
        //强制转换 事件是由哪个对象发出来的
        if(rdb.isSelected())//保证其中有一个按钮是被选中的
        {
            if (rdb.getText()=="Lines") {//也就是按钮的名称，做到匹配
            canvas.setTodoAction(0);//在中做得事件进行编号

            }
            else if (rdb.getText()=="rectangle") {
                canvas.setTodoAction(1);
            }
            else if (rdb.getText()=="circle") {
                canvas.setTodoAction(2);

            }//可以在此添加代码，新按钮
            else if (rdb.getText()=="move") {
                canvas.setTodoAction(100);
            }
        }
    }




/**
 * Create the application.
 */
public DrawingBroad() {//构造函数，
    initialize();
}

/**
 * Initialize the contents of the frame.
 */
private void initialize() {
    frame = new JFrame();
    frame.setBounds(100, 100, 800, 600);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JSplitPane splitPane = new JSplitPane();
    splitPane.setDividerLocation(160);
    frame.getContentPane().add(splitPane, BorderLayout.CENTER);

    canvas= new Canvas();
    splitPane.setRightComponent(canvas);


    JList<String> list = new JList<String>();
    splitPane.setLeftComponent(list);

    canvas.setLayers(list);

    JToolBar toolBar = new JToolBar();
    frame.getContentPane().add(toolBar, BorderLayout.NORTH);



    JRadioButton rdbtnLines = new JRadioButton("lines");
    rdbtnLines.setSelected(true);//首先选择一个按钮
    rdbtnLines.addItemListener(this);
    toolBar.add(rdbtnLines);

    JRadioButton rdbtnRectangle = new JRadioButton("rectangle");
    rdbtnRectangle.addItemListener(this);
    toolBar.add(rdbtnRectangle);

    JRadioButton rdbtnMove = new JRadioButton("move");
    rdbtnMove.addItemListener(this);
    toolBar.add(rdbtnMove);

    JRadioButton rdbtnCircle = new JRadioButton("circle");
    rdbtnCircle.addItemListener(this);
    toolBar.add(rdbtnCircle);


    ButtonGroup bg=new ButtonGroup();
    bg.add(rdbtnLines);
    bg.add(rdbtnRectangle);
    bg.add(rdbtnMove);
    bg.add(rdbtnCircle);






}

}
package ObjectPrinciple;

import java.awt.Color;

import java.awt.Graphics;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.util.ArrayList;

import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.event.MouseInputAdapter;
import javax.swing.event.MouseInputListener;

public class Canvas extends JPanel {
private int todoAction;
private Rectangle scope;
private ArrayList shapes;
private JList layers;

public void setLayers(JList<String> layers) {
    this.layers = layers;
}

public void setTodoAction(int todoAction) {
    this.todoAction = todoAction;
}

public Canvas() {

    shapes= new ArrayList<Shape>();
    addMouseMotionListener(mouseHandler);
    addMouseListener(mouseHandler);
}


public void paintShape(Shape s) {
    // TODO Auto-generated method stub
    shapes.add(s);
    String[] strings = new String[shapes.size()];
    int i=0;
    for (Shape shape:shapes) {
        strings[i++]=shape.toString();
    }
    layers.setListData(strings);    
    repaint(); 

}

private MouseInputListener mouseHandler = new MouseInputAdapter() {

    Point startPoint;

    @Override
    public void mousePressed(MouseEvent e) {
        // TODO Auto-generated method stub
        //初始化
        startPoint = e.getPoint();
        scope = new Rectangle();

    }



    @Override
    public void mouseReleased(MouseEvent e) {
        // TODO Auto-generated method stub
        //消除矩形框
        if(todoAction==100) {
            Moving m = shapes.get(layers.getSelectedIndex());
            m.move(e.getPoint().x, e.getPoint().y);

            scope = null;
            repaint();
        }
        else {

        setScope(startPoint,e.getPoint());
        if(scope.width > 0||scope.height>0)
            if(todoAction==0) {
                MyLine line = new MyLine();
                line.setShape(scope.x, scope.y, scope.width, scope.height, 0, "line");
                paintShape(line);
            }else if(todoAction == 1) {
                MyRectangle rectangle = new MyRectangle();
                rectangle.setShape(scope.x, scope.y, scope.width, scope.height, 1, "rectangle");
                paintShape(rectangle);
            }else if (todoAction == 2) {
                Circle circle= new Circle();
                circle.setShape(scope.x, scope.y, scope.width, scope.height, 2, "circle");
                paintShape(circle);
            }
        scope=null;
        repaint();
        }
    }
        @Override
        public void mouseDragged(MouseEvent e) {
        // TODO Auto-generated method stub


        if(scope==null) {
            setScope(startPoint, e.getPoint());
        }
        repaint();
        }











    private void setScope(Point starPoint,Point endPoint) {
        int x=Math.min(startPoint.x, endPoint.x);
        int y=Math.min(startPoint.y, endPoint.y);
        int w=Math.abs(startPoint.x - endPoint.x);
        int h=Math.abs(startPoint.y - endPoint.y);
        scope.setBounds(x,y,w,h);
    }

};

@Override
public void print(Graphics g) {
    // TODO Auto-generated method stub
    super.print(g);
    g.setColor(Color.BLACK);
    if(scope != null)
        g.drawRect(scope.x, scope.y, scope.width,scope.height);
//需要一个队列，需要把画的图形加到队列，调用每个元素的drawingshape方法
    for(Drawing d:shapes) {
        d.drawingShape(g);
    }
}

}

package ObjectPrinciple;

import java.awt.Graphics;

public interface Drawing {
public void drawingShape(Graphics g);
}
package ObjectPrinciple;

public interface Moving {
public void move(int x,int y);

}

package ObjectPrinciple;

public abstract class Shape implements Drawing,Moving{
//位置
int x,y;
//宽度，高度
int width,height;
int shapetype;
String shapename;
public void setShape(int x, int y, int width, int height, int shapetype, String shapename) {
//super();
this.x = x;
this.y = y;
this.width = width;
this.height = height;
this.shapetype = shapetype;
this.shapename = shapename;
}
@Override
public void move(int x, int y) {
// TODO Auto-generated method stub
this.x = x;
this.y = y;
}
@Override
public String toString() {
return shapename;
}

}
package ObjectPrinciple;

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Line2D;

public class MyLine extends Shape {

public void drawingShape(Graphics g) {
    Graphics2D g2d=(Graphics2D) g;
    Line2D line2d = new Line2D.Double(x,y,x+width,y+height);

    g2d.draw(line2d);



}

}

package ObjectPrinciple;

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.geom.Line2D;
import java.awt.geom.Rectangle2D;

public class MyRectangle extends Shape {

@Override
public void drawingShape(Graphics g) {
    // TODO Auto-generated method stub
    Graphics2D g2d=(Graphics2D) g;
    //Rectangle2D rect = new Line2D
    Rectangle2D rect = new Rectangle2D.Double(x,y,x+width,y+height);
    g2d.draw(rect);

}

}