[newbie] The type MouseComponent must implement the inherited abstract method MouseMotionListener...

[Jon Camilleri]

This is wot I see...

MouseTest.java
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.awt.geom.*;
import javax.swing.*;

public class MouseTest {
		public static void main (String[] args)
		{
			EventQueue.invokeLater(new Runnable()
			{
				public void run()
				{
					MouseFrame frame = new MouseFrame();
					frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
					frame.setVisible(true);
				}
			}
			);
		}
}



MouseFrame.java
import javax.swing.JFrame;

public class MouseFrame extends JFrame {
	public MouseFrame()
	{
		setTitle("Mouse Test");
		setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
		
		//add component to Frame
		MouseComponent component = new MouseComponent();
		add(component);
	}
	
	private static final int DEFAULT_WIDTH = 300;
	private static final int DEFAULT_HEIGHT = 200;
}


MouseComponent.java
import javax.swing.JComponent;
import java.awt.geom.*;
import java.awt.*;
import java.util.ArrayList;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;

/**
 * A component with mouse operations for adding and removing squares.
 * @author Administrator
 *
 */
public class MouseComponent extends JComponent implements MouseMotionListener {
	public MouseComponent() 
	{
		ArrayList<Rectangel2D> squares = new ArrayList<Rectangel2D>();
		current = null; 
		
		addMouseListener(new MouseHandler());
		//FIX what is MouseHandler?
		
		addMouseMotionListener(new MouseMotionListener());
		/*FIX MouseMotionListener() is an interface.
		  cannot instantiate? */
	}
	
	public void paintComponent (Graphics g)
	{
		Graphics2D g2 = (Graphics2D) g;
		
		//draw all squares
		for (Rectangle2D r : squares) 
			g2.draw(r);
	}
	
	/**
	 * Finds the first square containing a point.
	 * @param p: a point
	 * @return: the first square that contains p.
	 */
	public Rectangle2D find (Point2D p) {
		double x = p.getX();
		double y = p.getY();
		
		Rectangle2D current = new Rectangle2D.Double(x - SIDELENGTH / 2, y - SIDELENGTH / 2, SIDELENGTH, SIDELENGTH);
		squares.add(current);
		repaint();
	}
	
	/**
	 * Removes a square from the collection.  
	 * @param: s - the square to remove.
	 */
	public void remove (Rectangle2D s)
	{
		if (s == null) return;
		if (s == current) current = null;
		squares.remove(s);
		repaint();
	}
	
	private static final int SIDELENGTH = 10;
	private ArrayList<Rectangle2D> squares;
	private Rectangle2D current;
	

	private class MouseHandler extends MouseAdapter {
		public void mousePressed (MouseEvent event)
		{
			//add a new square if the cursor is not inside a square
			current = find(event.getPoint());
			if (current == null) add(event.getPoint()); //FIX error?
		}
		
		public void mouseClicked (MouseEvent event)
		{
			//remove the current square if double clicked
			current = find(event.getPoint());
			if ((current != null) && event.getClickCount() >= 2) remove(current); 
		}	
	}
	
	@SuppressWarnings("unused")
	private class MouseMotionHandler implements MouseMotionListener
	{
		public void mouseMoved (MouseEvent event) {
			//set the mouse cursor to cross hairs if it is inside a rectangle
			if (find(event.getPoint())==null ) setCursor(Cursor.getDefaultCursor());
			else setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
		}
		
		public void mouseDragged (MouseEvent event) {
			
			int x = 0;
			int y = 0;
			if (current != null) {
				x = event.getX();
				y = event.getY();
			}
			
			//drag the current rectangle to center it at (x,y)
			current.setFrame(x - SIDELENGTH / 2, y = SIDELENGTH / 2, SIDELENGTH, SIDELENGTH);
			repaint();
			
		}
	}
	
}

Output:
Exception in thread "AWT-EventQueue-0" java.lang.Error: Unresolved compilation problems:
The type MouseComponent must implement the inherited abstract method MouseMotionListener.mouseMoved(MouseEvent)
The type MouseComponent must implement the inherited abstract method MouseMotionListener.mouseDragged(MouseEvent)
Rectangel2D cannot be resolved to a type
Rectangel2D cannot be resolved to a type
Cannot instantiate the type MouseMotionListener
This method must return a result of type Rectangle2D
The method add(Component) in the type Container is not applicable for the arguments (Point)

at MouseComponent.<init>(MouseComponent.java:14)
at MouseFrame.<init>(MouseFrame.java:10)
at MouseTest$1.run(MouseTest.java:14)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

[Craig Wood]

Try changing this

public class MouseComponent extends JComponent implements MouseMotionListener {

to this

public class MouseComponent extends JComponent {

[Deepak Bala]

You code does not compile because of the following reasons

The type MouseComponent must implement the inherited abstract method MouseMotionListener.mouseMoved(MouseEvent)
The type MouseComponent must implement the inherited abstract method MouseMotionListener.mouseDragged(MouseEvent)
Rectangel2D cannot be resolved to a type
Rectangel2D cannot be resolved to a type
Cannot instantiate the type MouseMotionListener
This method must return a result of type Rectangle2D
The method add(Component) in the type Container is not applicable for the arguments (Point)

Use your IDE's quick hint or resolution techniques to fix the problem. Ctrl + 1 in eclipse. Click on the bulb on the sidebar in netbeans

[Campbell Ritchie]

If you are saying your object is a MouseMotionListener, then you are telling the compiler it has the 5 methods of that interface. Details here. So you have to implement 5 methods, even if some of them are empty, and you have to ensure that the method names are spelt correctly, same return type, etc. Remember they are all implicitly "public".