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Semester 1/Programming 1/Java/examples/projects/chapter01/figures/Triangle.java

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+import java.awt.*;
+
+/**
+ * A triangle that can be manipulated and that draws itself on a canvas.
+ * 
+ * @author  Michael Kölling and David J. Barnes
+ * @version 2016.02.29
+ */
+
+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 = 60;
+        width = 70;
+        xPosition = 210;
+        yPosition = 140;
+        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);
+        }
+    }
+}