1. More methods, more capabilities
Turtles
More methods, more capabilities
Copyright © Curt Hill

2. Introduction Basics were covered last time but there is more
Signatures
Coordinates
Constructors
Alternate methods
Pen motion
Colors
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3. Signatures A method signature consists of:
Name of the method
Number and type of the parameters
In most previous languages it was the name only
In Java two methods may have same name but must have different signatures
This is known as overloading
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4. Example The Turtle method forward has two signatures: forward(int k);
Move forward k pixels
forward();
Move forward 100 pixels
Thus:
Sam.forward(100); // and
Sam.forward();
Do exactly the same thing
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5. Coordinate Systems
The drawing surface is different than the coordinates used in algebra
The upper left corner is point (0,0)
The X coordinate gets larger as we go right
The Y gets larger as we go down
The default World is 640 pixels wide (x value) and 480 pixels high (y value)
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6. Default World Orientation
(0,0)
(640,0)
(0,480)
(640,480)
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7. World Sizes
The default constructor for World gives a 640 by 480 size panel World w = new World();
There is another constructor that allows different sizing: World w2 = new World(1000, 700);
This gives width of 1000 pixels and height of 700
Two constructors with two signatures
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8. Turtle Constructors The first constructor only used the world
The location defaulted to the center
Second gives the location and then world
Signature: Turtle(int x, int y, World w);
Example: yertle = new Turtle(50,50,myW);
Copyright © Curt Hill

9. Movement If you can move forward why not backward?
It has the same form:
backward(int pixels)
yertle.backward(50);
backward()
Moves 100 pixels backward
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10. Relative Movement Forward and backward are relative
Start at turtles location and move in the turtles current heading
There is also a moveTo method
Takes a target location and moves to that absolute location
Does not change heading
Ignores it
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11. Example
Consider the following code: World w = new World(500,300); Turtle t = new Turtle(80,150,w); t.turn(75); t.forward(); t.moveTo(200,200); t.forward(100);
This would produce the picture in next screen
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12. Example
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13. Commentary The last screen demonstrated A different sized world
Three parameter Turtle constructor
forward with no parameters
moveTo changing position but not heading
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14. Pen Movement After construction the pen is down
Thus any move leaves a trail
Two commands: penUp() penDown()
Like all methods the object must occur first: yertle.penUp(); yertle.forward(200); yertle.penDown();
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15. Hiding and displaying The hide() method will make the turtle invisible
This will not affect the previously drawn lines or the status of the pen up or down
The show() method will make the turtle visible
Also does not affect lines or pen status
Copyright © Curt Hill

16. Turning The turn method is the most useful but there are others
turnLeft() is the same as turn(-90)
turnRight() is the same as turn(90);
turnToFace(int x, int y) sets the heading so that the turtle is pointed at that location
turnToFace(Turtle) sets the heading so that the turtle is pointed at a second turtle
Copyright © Curt Hill

17. Another Example
The following code: World w = new World(500,300); Turtle t = new Turtle(100,150,w); t.turnRight(); t.forward(); t.penUp(); // Move but don't draw t.moveTo(200,200); t.penDown(); t.forward(100);
Produces next screen
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18. Example
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19. Colors The color of the turtle and the pen may be changed
This requires some knowledge of how Java handles colors
Almost everything in Java is a class
Color is a class as well
A color is produced on a monitor or screen by making each pixel glow with certain red, green and blue values
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20. Color Constructors Color(int red,int green, int blue);
All integers in range
The larger the value the brighter
255,255,255 is white
Color(int red, int green, int blue, int alpha);
Alpha is a transparency indicator
Used with multiple color planes
0 is black/invisible is bright/opaque
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21. Color Constructors
A constructor is always used following the new keyword
Most times this is in an assignment
But not usually when dealing with colors
Example: new Color(255, 0, 0)
This produces bright red
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22. Color Constants As a convenience several constant colors are available
black, blue, cyan, darkGray, gray, green, lightGray, etc
These must be referred to with a Color class or just Color prefixed Color.cyan
These may be all lower or all upper case
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23. Imports The Color class requires an import statement
import java.awt.Color; This is placed before the first public class
Placed after the package statement, if there is one
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24. Turtle colors
The setColor method changes the turtle color and the pen color
The parameter is either a color constant or a newly created special color: yertle.setColor(Color.RED); yertle.setColor(new Color(255, 128, 10));
Constants do not need the new
The constructor does need the new
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25. Example Notes The import statement is needed for colors
There is both a constant and constructor color
Use the constant ones for common colors
Use the constructor for greater refinement
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26. Example import java.awt.Color; public class TurtleExample2 {
public static void main(String []a){
World w = new World(500,300);
Turtle t = new Turtle(100,150,w);
t.turnRight();
t.forward();
t.setColor(Color.RED);
t.turn(90);
t.setColor(new Color(128,64,255));
t.forward(100); }
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27. What it looks like
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28. More Color Commands
The turtle icon does not have to match the pen color
setPenColor(Color) will change the pen color without changing the turtle color
setShellColor(Color) changes the turtle shell without changing the pen or feet color
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29. Line Width
So far our turtle has only drawn lines that are one pixel wide
This is OK and maybe even what we want
We can control the width with the setPenWidth(int) method
It takes an integer as a parameter
Example: yertle.setPenWidth(5)
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30. Example World w = new World(500,300);
Turtle t = new Turtle(100,150,w);
t.turnRight();
t.forward();
t.setColor(Color.RED);
t.setPenWidth(5);
t.turn(-90);
t.setColor(new Color(128,64,255));
t.forward(100);
t.setPenColor(Color.yellow);
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31. Result of Example Code
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32. Bounds The turtle must stay within the bounds of the world
If the turtle is pointed towards an edge and then moves forward it will exceed the edge
The turtle will then just disappear
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33. Summary
We can now create worlds of various sizes and turtles starting in different positions
The turtles can move with or without a trail
We have several ways to move them or turn them
We can make their trails and themselves any color we like
Copyright © Curt Hill