import java.awt.*;/** * A triangle that can be manipulated and that draws itself on a canvas. *  * @author  Michael Kolling and David J. Barnes * @version 2006.03.30 */public class Triangle{    private int height;    private int width;    private int xPosition;    private int yPosition;    private String color;    private boolean isVisible;    /**     * Create a new triangle at default position with default color.     */    public Triangle()    {        height = 30;        width = 40;        xPosition = 50;        yPosition = 15;        color = "green";        isVisible = false;    }    /**     * Make this triangle visible. If it was already visible, do nothing.     */    public void makeVisible()    {        isVisible = true;        draw();    }        /**     * Make this triangle invisible. If it was already invisible, do nothing.     */    public void makeInvisible()    {        erase();        isVisible = false;    }        /**     * Move the triangle a few pixels to the right.     */    public void moveRight()    {        moveHorizontal(20);    }    /**     * Move the triangle a few pixels to the left.     */    public void moveLeft()    {        moveHorizontal(-20);    }    /**     * Move the triangle a few pixels up.     */    public void moveUp()    {        moveVertical(-20);    }    /**     * Move the triangle a few pixels down.     */    public void moveDown()    {        moveVertical(20);    }    /**     * Move the triangle horizontally by 'distance' pixels.     */    public void moveHorizontal(int distance)    {        erase();        xPosition += distance;        draw();    }    /**     * Move the triangle vertically by 'distance' pixels.     */    public void moveVertical(int distance)    {        erase();        yPosition += distance;        draw();    }    /**     * Slowly move the triangle horizontally by 'distance' pixels.     */    public void slowMoveHorizontal(int distance)    {        int delta;        if(distance < 0)         {            delta = -1;            distance = -distance;        }        else         {            delta = 1;        }        for(int i = 0; i < distance; i++)        {            xPosition += delta;            draw();        }    }    /**     * Slowly move the triangle vertically by 'distance' pixels.     */    public void slowMoveVertical(int distance)    {        int delta;        if(distance < 0)         {            delta = -1;            distance = -distance;        }        else         {            delta = 1;        }        for(int i = 0; i < distance; i++)        {            yPosition += delta;            draw();        }    }    /**     * Change the size to the new size (in pixels). Size must be >= 0.     */    public void changeSize(int newHeight, int newWidth)    {        erase();        height = newHeight;        width = newWidth;        draw();    }    /**     * Change the color. Valid colors are "red", "yellow", "blue", "green",     * "magenta" and "black".     */    public void changeColor(String newColor)    {        color = newColor;        draw();    }    /**     * Draw the triangle with current specifications on screen.     */    private void draw()    {        if(isVisible) {            Canvas canvas = Canvas.getCanvas();            int[] xpoints = { xPosition, xPosition + (width/2), xPosition - (width/2) };            int[] ypoints = { yPosition, yPosition + height, yPosition + height };            canvas.draw(this, color, new Polygon(xpoints, ypoints, 3));            canvas.wait(10);        }    }    /**     * Erase the triangle on screen.     */    private void erase()    {        if(isVisible) {            Canvas canvas = Canvas.getCanvas();            canvas.erase(this);        }    }}