How can I update variable value that received from argument (perhaps, something like C++'s pointer)?

notalentgeek

I have this code.

http://pastebin.com/HU1agrXJ

What happened now is that when I increase the value of i the value of test.i will always be the same as it was first time assigned.

What I want is that when I update the value of i the value of test.i is also updated.

I was thinking perhaps assigning the address reference instead of the value will solve this problem. But how can I do this in Java/Processing? Is there any alternative rather than assigned the value over time (the Test object will be around ~1000 in amount)?

quark

The code is short enough to show in this forum and it will make it easier for members to discuss it, so here it is

class Test {

  int i = 0;
  int j = 0;
  Test(int _i, int _j) {

    i = _i;
    j = _j;
  }
  Test() {
  }
}

int i = 0;
int j = 0;
Test test = new Test(i, j);
void setup() {
}
void draw() {

  i ++;
  j ++;
  println(

    i + " " + j + " " +
    test.i + " " + test.j

    );
}

quark

Unfortunately for you its is not possible to link the i in Test to the global i Java does not support C style pointers. Since you want these 2 variables always to have the same value why have them as separate variables?

notalentgeek

How can I use one variable for several different classes?

Let say I have a private function named PrivateFunction(int _i){} in Test class. How can I get int _i filled from a value outside of Test class?

Meta question, how can you show code in this forum?

GoToLoop

http://forum.Processing.org/two/discussion/8045/how-to-format-code-and-text

benja

If you really want to pass a only a reference, you could create an array of length one. Unlike primitive datatypes, arrays and objects are passed by reference.

class Test {
  int i[] = {0};
  Test(int[] _i) {
    i = _i;
  }
}

int i[] = {0};
Test test = new Test(i);
void setup() {
}
void draw() {
  i[0] ++;
  println(i[0] + " " + test.i[0] );
}

But i don't have any idea where this could be useful at the moment.

GoToLoop

Unlike primitive datatypes, arrays and objects are passed by reference.

Some pedantic observations: :-B

1. Arrays are also object types but w/o a formal class which represents it. Only thru' [] operator.
2. Pass-by-reference doesn't mean passing some value which represents any reference.
3. Rather it's when we pass the reference/pointer of variables themselves. Which Java can't!
4. In other words, pass-by-reference is the same as passing a variable's own memory address.

quark

How can I use one variable for several different classes?

In Processing any class defined inside a pde tab is an inner class so has access to any variables declared in the sketch. The sketch below 2 classes sharing the same variables.

class TestA {

  void printIJ() {
    println("TestA " + i+ "  " + j);
  }
}

class TestB {

  void printIJ() {
    println("TestB " + i+ "  " + j);
  }
}


int i = 0;
int j = 0;
TestA a = new TestA();
TestB b = new TestB();

void setup() {
  frameRate(5); // Just slow the output down
}

void draw() {
  i ++;
  j ++;
  println("\nGlobal " + i + " " + j + " ");
  a.printIJ();
  b.printIJ();
}

The output was

Global 1 1 
TestA 1  1
TestB 1  1

Global 2 2 
TestA 2  2
TestB 2  2

Global 3 3 
TestA 3  3
TestB 3  3

...

notalentgeek

Cool! Okay, now if I want to pass primitive data - type I just need to make it a global variable. However, if the data - type is an object it will automatically pass a reference instead of value in Java.

GoToLoop

... now if I want to pass primitive datatype I just need to make it a global variable.

1. Java doesn't have "global" variables but fields. Which are also known as properties in JS.
2. Fields, methods & constructors are class members.
3. Processing's "sketch" is an instance of class PApplet. More precisely, a subclass of it.
4. Therefore its "global" variables are in fact PApplet fields.

... if the datatype is an object it will automatically pass a reference instead of value in Java.

1. Even references/pointers are values. Datatype determines how values are interpreted.
2. Java doesn't allow references of variables being stored nor passed around though.