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Thread: Moving a shape across a panel

  1. #1
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    Default Moving a shape across a panel

    Since I am pretty new to Java I have encountered some very trivial problems. I am working harder than I thought I would just to stay up with my class, but beyond that I need some help determining why my program is not working right. I am to create a graphics panel with two JSliders (one vertical, one horizontal) which will move a ball with the thumbnail of the slider. I have created a circle, but when I try to move the circle across the panel, instead of it moving, the size of the circle gets bigger, smaller, bigger, and so on. It appears to resize diagonally across the panel. Please let me know if my listener needs a loop, do I put a loop in the paintComponent method, do I create a new method to move the shape? Here is my code:

    import java.awt.Color;
     
     
    public class Week06 {
    	private JFrame myFrame;
    	private final GPanel gP = new GPanel();
    	private final JSlider vSlider = new JSlider(SwingConstants.VERTICAL, 0, 100, 0);
    	private final JSlider hSlider = new JSlider(SwingConstants.HORIZONTAL, 0, 100, 0);
    	private final JButton btnExit = new JButton("Exit");
    	private int x_pos = 10;
    	private int y_pos = 100;
    	private int radius = 10;
     
    	/**
    	 * Launch the application.
    	 */
    	public static void main(String[] args) {
    		EventQueue.invokeLater(new Runnable() {
    			public void run() {
    				try {
    					Week06 window = new Week06();
    					window.myFrame.setVisible(true);
    				} catch (Exception e) {
    					e.printStackTrace();
    				}
    			}
    		});
    	}
     
    	/**
    	 * Create the application.
    	 */
    	public Week06() {
    		initialize();
    	}
     
    	/**
    	 * Initialize the contents of the frame.
    	 */
    	private void initialize() {
    		myFrame = new JFrame();
    		myFrame.setTitle("06");
    		myFrame.setBounds(100, 100, 780, 495);
    		myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    		myFrame.getContentPane().setLayout(null);
     
    		//JPanel pnlBallMover = new JPanel();
    		gP.setBackground(new Color(0, 206, 209));
    		gP.setBorder(new MatteBorder(5, 5, 5, 5, (Color) new Color(222, 184, 135)));
    		gP.setBounds(10, 11, 714, 374);
    		myFrame.getContentPane().add(gP);
     
    		//JButton btnExit = new JButton("Exit");
    		btnExit.addActionListener(new ActionListener() {
    			public void actionPerformed(ActionEvent arg0) {
    				System.exit(0);
    			}
    		});
    		btnExit.setFont(new Font("Lucida Calligraphy", Font.BOLD, 16));
    		btnExit.setBounds(644, 413, 110, 33);
    		myFrame.getContentPane().add(btnExit);
     
    		hSlider.addChangeListener(new ChangeListener() {
    			public void stateChanged(ChangeEvent arg0) {
    				gP.repaint();
     
    			}
    		});
     
     
    		hSlider.setBounds(0, 0, 714, 23);
    		hSlider.setMajorTickSpacing(5);
    		hSlider.setPaintTicks(true);
    		myFrame.getContentPane().add(hSlider);
     
    		//JSlider vSlider = new JSlider();
    		vSlider.addChangeListener(new ChangeListener() {
    			public void stateChanged(ChangeEvent e) {
    				gP.repaint();
     
     
    			}
    		});
    		vSlider.setOrientation(SwingConstants.VERTICAL);
    		vSlider.setBounds(x_pos, y_pos, 30, 374);
    		vSlider.setMajorTickSpacing(5);
    		vSlider.setPaintTicks(true);
    		vSlider.setInverted(true);
    		myFrame.getContentPane().add(vSlider);
    	}
     
    	private class GPanel extends JPanel {
    		public void paintComponent(Graphics g) {
    			super.paintComponent(g);
    			Graphics2D g2 = (Graphics2D) g;
     
    			g2.setColor(Color.ORANGE);
    			g2.fillOval(x_pos - radius, y_pos - radius, radius*2, radius*2);
    			gP.setD(radius*2);
     
    			//gP.repaint();
     
    			int fw = myFrame.getWidth();
    			int fh = myFrame.getHeight();
    			if((fw - 66 > 10) && (fh - 121 > 10)) {
    				btnExit.setBounds(fw - 136, fh - 82, 110, 33);
    				hSlider.setBounds(10, fh - 110, fw - 66, 23);
    				vSlider.setBounds(fw - 56, 11, 30, fh - 121);
    				setBounds(10, 11, fw - 66, fh - 121);
    			}
    		}
    		public void setD(int newD) {
    			if(newD >= 0) {
    				radius = newD;
    			} else {
    				radius = 10;
    			}
    		}
    		public Dimension getPreferredSize() {
    			return new Dimension(100, 100);
    		}
    		public Dimension getMinimumSize() {
    			return getPreferredSize();
    		}
    	}
    }
    Last edited by havinFun; May 15th, 2012 at 10:11 PM.


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Moving a shape across a panel

    instead of it moving, the size of the circle gets bigger, smaller, bigger,
    If you want the size of the shape not to change, try defining the radius as final and remove all code that tries to change its value . Only change the x and y position values.


    BTW The code you posted does not compile without many errors. Its missing several import statements.
    Last edited by Norm; May 16th, 2012 at 06:18 AM.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Moving a shape across a panel

    Sorry, didn't realize that my imports were missing, here is the complete code:
    import java.awt.Color;
    import java.awt.Dimension;
    import java.awt.EventQueue;
    import java.awt.Font;
    import java.awt.Graphics;
    import java.awt.Graphics2D;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import javax.swing.JButton;
    import javax.swing.JFrame;
    import javax.swing.JPanel;
    import javax.swing.JSlider;
    import javax.swing.SwingConstants;
    import javax.swing.border.MatteBorder;
    import javax.swing.event.ChangeEvent;
    import javax.swing.event.ChangeListener;
     
     
    public class Week06 {
    	private JFrame myFrame;
    	private final GPanel gP = new GPanel();
    	private final JSlider vSlider = 
    			new JSlider(SwingConstants.VERTICAL, 0, 100, 0);
    	private final JSlider hSlider = 
    			new JSlider(SwingConstants.HORIZONTAL, 0, 100, 0);
    	private final JButton btnExit = 
    			new JButton("Exit");
    	private int x_pos = 10;
    	private int y_pos = 100;
    	private int radius = 10;
     
    	/**
    	 * Launch the application.
    	 */
    	public static void main(String[] args) {
    		EventQueue.invokeLater(new Runnable() {
    			public void run() {
    				try {
    					Week06 window = new Week06();
    					window.myFrame.setVisible(true);
    				} catch (Exception e) {
    					e.printStackTrace();
    				}
    			}
    		});
    	}
     
    	/**
    	 * Create the application.
    	 */
    	public Week06() {
    		initialize();
    	}
     
    	/**
    	 * Initialize the contents of the frame.
    	 */
    	private void initialize() {
    		myFrame = new JFrame();
    		myFrame.setTitle("Week06");
    		myFrame.setBounds(100, 100, 780, 495);
    		myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    		myFrame.getContentPane().setLayout(null);
     
    		//JPanel pnlBallMover = new JPanel();
    		gP.setBackground(new Color(0, 206, 209));
    		gP.setBorder(new MatteBorder(5, 5, 5, 5, 
    				(Color) new Color(222, 184, 135)));
    		gP.setBounds(10, 11, 714, 374);
    		myFrame.getContentPane().add(gP);
     
    		//JButton btnExit = new JButton("Exit");
    		btnExit.addActionListener(new ActionListener() {
    			public void actionPerformed(ActionEvent arg0) {
    				System.exit(0);
    			}
    		});
    		btnExit.setFont(new Font("Lucida Calligraphy", Font.BOLD, 16));
    		btnExit.setBounds(644, 413, 110, 33);
    		myFrame.getContentPane().add(btnExit);
     
    		hSlider.addChangeListener(new ChangeListener() {
    			public void stateChanged(ChangeEvent arg0) {
    				gP.repaint();
    			}
    		});
     
    		hSlider.setBounds(0, 0, 714, 23);
    		hSlider.setMajorTickSpacing(5);
    		hSlider.setPaintTicks(true);
    		myFrame.getContentPane().add(hSlider);
     
    		vSlider.addChangeListener(new ChangeListener() {
    			public void stateChanged(ChangeEvent e) {
    				gP.repaint();
    			}
    		});
    		vSlider.setOrientation(SwingConstants.VERTICAL);
    		vSlider.setBounds(x_pos, y_pos, 30, 374);
    		vSlider.setMajorTickSpacing(5);
    		vSlider.setPaintTicks(true);
    		vSlider.setInverted(true);
    		myFrame.getContentPane().add(vSlider);
    	}
     
    	private class GPanel extends JPanel {
    		public void paintComponent(Graphics g) {
    			super.paintComponent(g);
    			Graphics2D g2 = (Graphics2D) g;
     
    			g2.setColor(Color.ORANGE);
    			g2.fillOval(x_pos, y_pos, radius*2, radius*2);
    			gP.setD(radius*2);
     
    			int fw = myFrame.getWidth();
    			int fh = myFrame.getHeight();
    			if((fw - 66 > 10) && (fh - 121 > 10)) {
    				btnExit.setBounds(fw - 136, fh - 82, 110, 33);
    				hSlider.setBounds(10, fh - 110, fw - 66, 23);
    				vSlider.setBounds(fw - 56, 11, 30, fh - 121);
    				setBounds(10, 11, fw - 66, fh - 121);
    			}
    		}
    		public void setD(int newD) {
    			if(newD >= 0) {
    				radius = newD;
    			} else {
    				radius = 10;
    			}
    		}
    		public Dimension getPreferredSize() {
    			return new Dimension(100, 100);
    		}
    		public Dimension getMinimumSize() {
    			return getPreferredSize();
    		}
    	}
    }

    When I tried to declare "radius" as a final, I couldn't get to it in the setD method to work, when I try to remove this method then nothing happens when I move the slider. Do I set the sliders to (0, 0, ...,...)? or leave the x_pos and y_pos in there as well as in the set bounds for the oval?

  4. #4
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    Default Re: Moving a shape across a panel

    What is the setD method supposed to do? Why does it change the value of radius? Do you know what a circle's radius is?

    If you want the sliders to control the position of the shape, then you need to get the sliders values and use them to set the shape's x,y location values.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Moving a shape across a panel

    the setD is to make sure that the radius is never a negative number and if it is then default to a radius of 10, but I see now that I am hard coding the size of the circle so I should need to have this method. If I need to get the slider value, am I creating a method getValue() that will get the value of the veritcal and horizontal slider and then put that variable in the fillOval()?

  6. #6
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    Default Re: Moving a shape across a panel

    make sure that the radius is never a negative number
    Does the size of the drawn shape change?

    Where do you change the value of the x and y position of the shape? Is its position supposed to change when a slider is moved?
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Moving a shape across a panel

    I do not want the size to ever change. I am not sure where I want the value to change of the shape, am I going to reference the center of the shape or the x and y position (top left corner of shape)? The position is supposed to move with the slider, if the vertical slider is moved down, the shape should also move down and stop where the thumbnail is stopped, does that make sense?

  8. #8
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    Default Re: Moving a shape across a panel

    I do not want the size to ever change.
    Make radius final and you won't be able to change it.
    The position is supposed to move with the slider
    Your code is not using any values from the slider to change the x & y values of the shape's location.
    Look at the JSlider class's API doc for methods to use to get its value.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Moving a shape across a panel

    OK, so I looked at the API doc for JSlider, from what I get I am supposed to create a method getValue() create an int that will grab slider.getValue. Am I on the right track? Then I will return that int. I will then need to create a setValue(int) method that will place the slider at a value?

  10. #10
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    Default Re: Moving a shape across a panel

    To help you see what the JSlider methods do, add a println statement in the listener method and print out the values that the JSlider class methods return as you move the slider around.
    If you don't understand my answer, don't ignore it, ask a question.

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