How to pass variables as parameters - variables

Question

I have two bits of code
Tree tree;
void setup() {
int SZ = 512; // screen size
int d = 2;
int x = SZ/2;
int y = SZ;
size(SZ,SZ);
background(255);
noLoop();
tree = new Tree(d, x, y);
}
void draw() {
tree.draw();
}
and also
class Tree {
// member variables
int m_lineLength; // turtle line length
int m_x; // initial x position
int m_y; // initial y position
float m_branchAngle; // turtle rotation at branch
float m_initOrientation; // initial orientation
String m_state; // initial state
float m_scaleFactor; // branch scale factor
String m_F_rule; // F-rule substitution
String m_H_rule; // H-rule substitution
String m_f_rule; // f-rule substitution
int m_numIterations; // number of times to substitute
// constructor
// (d = line length, x & y = start position of drawing)
Tree(int d, int x, int y) {
m_lineLength = d;
m_x = x;
m_y = y;
m_branchAngle = (25.7/180.0)*PI;
m_initOrientation = -HALF_PI;
m_scaleFactor = 1;
m_state = "F";
m_F_rule = "F[+F]F[-F]F";
m_H_rule = "";
m_f_rule = "";
m_numIterations = 5;
// Perform L rounds of substitutions on the initial state
for (int k=0; k < m_numIterations; k++) {
m_state = substitute(m_state);
}
}
void draw() {
pushMatrix();
pushStyle();
stroke(0);
translate(m_x, m_y); // initial position
rotate(m_initOrientation); // initial rotation
// now walk along the state string, executing the
// corresponding turtle command for each character
for (int i=0; i < m_state.length(); i++) {
turtle(m_state.charAt(i));
}
popStyle();
popMatrix();
}
// Turtle command definitions for each character in our alphabet
void turtle(char c) {
switch(c) {
case 'F': // drop through to next case
case 'H':
line(0, 0, m_lineLength, 0);
translate(m_lineLength, 0);
break;
case 'f':
translate(m_lineLength, 0);
break;
case 's':
scale(m_scaleFactor);
break;
case '-':
rotate(m_branchAngle);
break;
case '+':
rotate(-m_branchAngle);
break;
case '[':
pushMatrix();
break;
case ']':
popMatrix();
break;
default:
println("Bad character: " + c);
exit();
}
}
// apply substitution rules to string s and return the resulting string
String substitute(String s) {
String newState = new String();
for (int j=0; j < s.length(); j++) {
switch (s.charAt(j)) {
case 'F':
newState += m_F_rule;
break;
case 'H':
newState += m_F_rule;
break;
case 'f':
newState += m_f_rule;
break;
default:
newState += s.charAt(j);
}
}
return newState;
}
}
This isn't assessed homework, it's an end of chapter exercise but I'm very stuck.
I want to "extend the Tree constructor so that values for all of the Tree member variables can be passed in as parameters."
Whilst I understand what variables and parameters are, I'm very stuck as to what to begin reading / where to begin editing the code.
One thing that has confused me and made me question my understanding is that, if I change the constructor values, (for example m_numiterations = 10;), the output when the code is run is the same.
Any pointers in the right direction would be greatly appreciated.

Answer 1

You already have everything in there to add more stuff to your Tree.
You see, in your setup(), you call:
tree = new Tree(d, x, y);
Now, that line, is actually calling the contructor implemented here:
Tree(int d, int x, int y) {
m_lineLength = d;
m_x = x;
etc....
So, if you want you can change that constructor to accept any variable that you want to pass from setup()
For instance, Tree(int d, int x, int y, String word, float number, double bigNumber)
Try experimenting with that. If you have any questions, PM me
EDIT
Let me add a little more flavor to it:
You see constructors are the way to initialize your class. It does not matter the access level (protected, public, private) or the number of constructors.
So, for example, Let's say you have this class with two public fields:
public class Book
{
public String Author;
public String Title;
public Book(String title, String author)
{
this.Title = title;
this.Author = author;
}
public Book()
{
this("Any title");//default title
}
}
Here, you can create books with both author and title OR only title! isn't that great? You can create things that are not inclusively attached to other things!
I hope you understand this. But, basically the idea is to encapsulate everything that matters to a certain topic to its own class.
NEW EDIT
Mike, you see, according to your comment you added this line:
int m_numIterations = 25;
The thing is that what you just did was only create a variable. A variable holds the information that you eventually want to use in the program. Let's say you are in high school physics trying to solve a basic free fall problem. You have to state the gravity, don't you?
So, in your notebook, you would go:
g = 9.8 m/s^2
right? it is a constant. But, a variable that you will use in your problem.
Well, the same thing applies in programming.
You added the line. That means that now, you can use it in your problem.
Now, go to this line,
tree = new Tree(d, x, y);
and change it to:
tree = new Tree(d, x, y, m_numIterations);
As you can see, now you are ready to "use" your variable in your tree. However! you are not done yet. You have to update as well your constructor because if not, the compiler will complain!
Go to this line now,
Tree(int d, int x, int y) {
m_lineLength = d;
m_x = x;
....
And change it to:
Tree(int d, int x, int y, int iterations) {
m_lineLength = d;
m_x = x;
....
You, see, now, you are telling your tree to accept a new variable call iterations that you are setting from somewhere else.
However! Be warned! There is a little problem with this :(
You don't have any code regarding the use of that variable. So, if you are expecting to actually see something different in the Tree, it won't happen! You need to find a use to the variable within the scope of the Tree (the one that I called iterations). So, first, find a use for it! or post any more code that you have to help you solve it. If you are calling a variable iterations, it is because you are planning to use a loop somewhere, amirite? Take care man. Little steps. Be patient. I added a little more to the Books example. I forgot to explain it yesterday :p