Java-在菜单中选择形状并在JPanel中绘制

Question

I wanted to implement a menu in my JFrame where I can select which shape to draw. I have a class extending JFrame and a class extending JPanel: So in my frame I add the menu and the panel, simple as that. To discriminate between different shapes, I use an Enum object with 4 values (Rect, Ellipse, Line and FreeHand).

The problem is that I cannot understand how to draw the shape on the JPanel, because I have a class MyShape and 4 different classes extending MyShape that overload MyShape's functions for the different shapes behaviours.

Can you check my code and suggest me the best way to do it?

Thank you!

Here is my code:

MyFrame.java

public class MainFrame extends JFrame implements Runnable,ActionListener {

JMenuBar menuBar;
JMenu menu;
JMenu subMenu = new JMenu();
JMenu subMenu2 = new JMenu();

JMenuItem menuItemActionsDraw;
JMenuItem menuItemActionsMove;
JMenuItem menuItemActionsResize;
JMenuItem menuItemActionsDel;

JMenuItem menuItemRect;
JMenuItem menuItemOval;
JMenuItem menuItemLine;
JMenuItem menuItemFreeHand;

DrawingArea area;

public MainFrame(){

}

public static void main(String[] args) {
    // TODO Auto-generated method stub
    MainFrame mframe = new MainFrame();
    SwingUtilities.invokeLater(mframe);

}

@Override
public void run() {
    // TODO Auto-generated method stub
    final JFrame jf = new JFrame("ShapeDraw");
    area = new DrawingArea();

    createMenu();
    jf.setJMenuBar(menuBar);
    jf.add(area);

    jf.pack();
    jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    jf.setVisible(true);

}   

@Override
public void actionPerformed(ActionEvent arg0) {
    // TODO Auto-generated method stub
    JMenuItem source = (JMenuItem)(arg0.getSource());

    if (source.equals(menuItemActionsDraw)){

    }
    else if (source.equals(menuItemActionsMove)){

    }
    else if (source.equals(menuItemActionsResize)){

    }
    else if (source.equals(menuItemActionsDel)){

    }
    else if (source.equals(menuItemRect)){
        //MyRect rect = new MyRect(x, y, width, heigth);
        DrawingArea.shape = EnumShapes.RECT;

    }
    else if (source.equals(menuItemOval)){

    }
    else if (source.equals(menuItemLine)){

    }
    else if (source.equals(menuItemFreeHand)){

    }
}

public void createMenu(){
    menuBar = new JMenuBar();
    menu = new JMenu("Menu");

    subMenu = new JMenu("Actions");

    menuItemActionsDraw = new JMenuItem("Draw");
    menuItemActionsMove = new JMenuItem("Move");
    menuItemActionsResize = new JMenuItem("Resize");
    menuItemActionsDel = new JMenuItem("Delete");

    menuItemRect = new JMenuItem("Rect");
    menuItemOval = new JMenuItem("Oval");
    menuItemLine = new JMenuItem("Line");
    menuItemFreeHand= new JMenuItem("FreeHand");

    subMenu.add(menuItemActionsDraw);
    subMenu.add(menuItemActionsMove);
    subMenu.add(menuItemActionsResize);
    subMenu.add(menuItemActionsDel);

    menuItemActionsDraw.addActionListener(this);
    menuItemActionsMove.addActionListener(this);
    menuItemActionsResize.addActionListener(this);
    menuItemActionsDel.addActionListener(this);

    menu.add(subMenu);

    subMenu2 = new JMenu("Shapes");

    menuItemRect.addActionListener(this);
    menuItemOval.addActionListener(this);
    menuItemLine.addActionListener(this);
    menuItemFreeHand.addActionListener(this);

    subMenu2.add(menuItemRect);
    subMenu2.add(menuItemOval);
    subMenu2.add(menuItemLine);
    subMenu2.add(menuItemFreeHand);

    menu.add(subMenu2);

    menuBar.add(menu);
}
}

DrawingArea.java

public class DrawingArea extends JPanel implements MouseInputListener, MouseMotionListener {

public ArrayList<MyShape> displayList = new ArrayList<MyShape>();
public static EnumShapes shape;
public MyRect rect;
public Graphics2D g2d;

public DrawingArea() {
    super();
    this.setLayout(new BorderLayout());
    super.setPreferredSize(new Dimension(500,500));
    setBorder(BorderFactory.createLineBorder(Color.black));

    addMouseListener(this);
    addMouseMotionListener(this);
}

@Override
public void paintComponent(Graphics g){

}

@Override
public void mouseClicked(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mouseEntered(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mouseExited(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mousePressed(MouseEvent arg0) {
    // TODO Auto-generated method stub
    switch(shape){
    case RECT:
        rect = new MyRect(arg0.getX(), arg0.getY(), 0, 0);
    case OVAL:
        // to do stuff
    case LINE:
        // to do stuff
    case FREEHAND:
        // to do stuff
    default:
        break;
    }
    repaint();

}

@Override
public void mouseReleased(MouseEvent arg0) {
    // TODO when finished dragging, add shape to displayList
    //displayList.add(rect);
}

@Override
public void mouseDragged(MouseEvent arg0) {
    // TODO while mouse is dragged, set new width and height and repaint

    // I should use x and y and calculate the distance between x2 and y2,
    // and then set the difference as width and height

    switch(shape){
    case RECT:
        rect.setWidthHeight(arg0.getX()-rect.x, rect.y-arg0.getY());
        rect.draw(g2d);
    case OVAL:
        // to do stuff
    case LINE:
        // to do stuff
    case FREEHAND:
        // to do stuff
    default:
        break;
    }
}

@Override
public void mouseMoved(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

public void setShape(EnumShapes shape){
    this.shape = shape;
}
}

MyShape.java

public abstract class MyShape {
protected int x;
protected int y;
protected int width;
protected int height;
protected EnumShapes shape;

public MyShape(int x, int y, int width, int height){
    this.x=x;
    this.y=y;
    this.width=width;
    this.height=height;
}

public abstract void draw(Graphics2D g);
public abstract void fill(Graphics2D g);
public abstract void setFrame(double x, double y, double width, double height);
public abstract void drawSelectionBox(Graphics2D g);

public void setWidthHeight(int width, int height) {
    // TODO Auto-generated method stub
    this.width = width;
    this.height = height;
}

}

MyRect.java

public class MyRect extends MyShape {

public MyRect(int x, int y, int width, int height) {
    super(x, y, width, height);
    // TODO Auto-generated constructor stub
}

@Override
public void draw(Graphics2D g) {
    // TODO Auto-generated method stub
    g.drawRect(x, y, width, height);
}

@Override
public void fill(Graphics2D g) {
    // TODO Auto-generated method stub

}

@Override
public void setFrame(double x, double y, double width, double height) {
    // TODO write stuff

}

@Override
public void drawSelectionBox(Graphics2D g) {
    // TODO write stuff

}
}

Answer 1

"The problem is that I cannot understand how to draw the shape on the JPanel, because I have a class MyShape and 4 different classes extending MyShape that overload MyShape's functions for the different shapes behaviours."

Have a MyShape selectedShape; in your DrawingArea class. And have a setter for it

public void setSelectedShape(MyShape selectedShape) {
    this.selectedShape = selectedShape;
    repaint();
}

You can paint the selected shape

protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D)g;
    if (selectedShaped != null) {
        selectedShape.draw(g2);
    }
}

Just call the setSelectedShape method from a listener in your frame class, whenever you want to draw a different shape.

If your shapes have different methods (other than those defined in the abstract class) you may want to invoke, check instanceof

if (selectedShape instanceof MyRect) {
    // do something
}