CS111 Lab 4

Wednesday, February 19, 2003

• Invocation trees
• PictureWorld examples
• Divide/Conquer/Glue

EXERCISE 1: Invocation Tree

Given the following code below, draw an invocation tree for [LBW1].run(), where [LBW1] is an instance of LabBuggleWorld in Object Land.

public class LabBuggleWorld extends BuggleWorld {
  public void run () {
    LabBuggle diana = new LabBuggle();
    diana.forward(2);
    diana.turnAround();
    double d = diana.jump(2,3);
    diana.forward(3);
    boolean isBagel = diana.isOverBagel();
  }
}
   
   class LabBuggle extends Buggle {
   
  public void turnAround () {
    this.left();
    this.left();
  }
   
  public double jump (int right, int up) {
    Point p = this.getPosition();
    this.setPosition(new Point(p.x+right, p.y+up));
    return this.distanceFromStart();
  }
   
  public double distanceFromStart () {
    Point p = getPosition();
    int x = p.x-1;
    int y = p.y-1;
    return Math.sqrt((x*x)+(y*y));
  }
   
}

EXERCISE 2: Escher Knitting Patterns

For exercises 2 and 3 please download the folder lab4_programs from the download directory on cs111 server.

Recall that the two basic patterns are:

A(red,blue,green,yellow,magenta)

B(red,blue,green,yellow,magenta)

Below are three practice knitting patterns to figure out. The skeletons for the methods are in the LabKnitWorld.java file.

Task 2 Fill in the code for these methods to obtain the patterns. Consult Picture World contract if necessary.

labKnit1(Color.red, Color.green)	labKnit2(Color.magenta, Color.blue)
labKnit3(Color.blue, Color.red, Color.cyan, Color.magenta)

EXERCISE 3: Simple QuiltWorld Patterns

First, a gentle introduction to quilting (Tasks 3a & 3b):

Task 3a Suppose you are given the following black box method:

public Picture triangle (Color c)
Returns a Picture of a triangle of the specified Color whose vertices are at (0,0), (1,0), and (0,1).

For example,

triangle(Color.green);

Using only the methods in the PictureWorld contract, write (on paper) the expressions which will return the following Pictures:

picture 1

picture 2

picture 3

Task 3b

Evaluate the following expressions. Draw (on paper) the Picture that each represents. Indicate the colors in whatever way is convenient (colored pencils, markers,etc.). Do not write a program to run on the computer to show you the pictures; do it by hand!

picture 4

overlay(clockwise90(triangle(Color.blue)),triangle(Color.blue));

picture 5

above(fourSame(flipDiagonally(triangle(Color.yellow))),
      beside(triangle(Color.green),
             above(empty(), flipVertically(triangle(Color.green)))));

Task 3c

To test your code, move the file LabQuiltWorld.html to the topmost position in Link Order in your project.

diamonds()

fourColors()