ArrayList of ArrayLists (dynamic 2D array) of custom class

[josephh]

Yes this can get confusing so here’s a link explaining that :

Reference Variable in Java - GeeksforGeeks

[ProgrammingN00b]

Hmmm …
I need some time to think about these things …
I’ll let you know if I hve more questions …

(I can see now why some people have a “distaste” for java …)

[GoToLoop]

@ProgrammingN00b

(I can see now why some people have a “distaste” for Java …)

If how reference behaves under Java was the reason why Java isn’t liked much folks would also hate JavaScript, Python and almost all modern programming languages!

Actually programmers tend to dislike Java b/c we have to explicitly declare the datatype of each single variable just like old C/C++ do!

BtW I’ve got some previous posts about Java’s reference aliases below:

Boolean trouble or something

Variables/fields/parameters store a single value. They range from 1 byte to 8 bytes in most languages. At the statement m = new PVector(); the operator new creates a contiguous memory block enough to fit in all PVector’s non-static fields. And when it’s done, it returns the 1st memory address of that block. And finally, that 1st memory address is stored in the field m as a reference value. Now, when you do pressLoc = m, you’re assigning field pressLoc w/ the exact value of m. After that assign…

Final array is being changed

Some of my clone() examples I did a long time ago at the link below may help ya out: https://Forum.Processing.org/two/discussion/12044/how-do-i-copy-out-one-row-of-a-2d-array-into-a-1d-array final int[][] stuff = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9} }; final int[] myArray = stuff[2]; // it's an alias for stuff[2]. myArray[0] = 10; // thus it alters stuff[2] too! println(stuff[2][0]); // prints out 10. stuff[2] is also affected! final int[] myClone = stuff[2].clone(); // it's a clon…

Final array is being changed

The 1st example explains at its comments why the 2nd 1 works. Processing got nothing to do w/ that, but the Java language itself! As you know by now, the 1st example already got those basic insights. Basically, we can have more than 1 variable (and array slots) pointing at the same object. They simply become alias for the same object. That is, if we mutate an object via 1 of its alias, its other aliases see those changes as well, b/c they all store th…

How do I pass a function by reference and then call it?

Actually JS functions, just like Java’s, are ALWAYS pass by value, regardless it’s a primitive or object datatype. When we pass a variable as a single argument to a function, the current value stored in that variable is read, and then the invoked function’s receiving parameter is initialized w/ a copy of that read value. B/c a function’s parameter can only receive a copy of the current value stored in a passed variable, reassigning another value to that local parameter won’t replace the value…

[josephh]

@GoToLoop

If how reference behaves under Java was the reason why Java isn’t liked much folks would also hate JavaScript, Python and almost all modern programming languages!

Nice point here!

@ProgrammingN00b Java is relatively easy compared to C++ believe me

[ProgrammingN00b]

Well, I am just very much used to Var1 = Var2 only “copying” the value of Var2 into Var1 …

[GoToLoop]

@ProgrammingN00b

… only “copying” the value of Var2 into Var1 …

That’s exactly the assign operator = does:

It replaces the value of the variable from the left side w/ a copy of the value from the right side.

But depending on the left variable’s datatype that value is interpreted differently.

If it’s a primitive datatype that value is interpreted as a number.

Otherwise it’s interpreted as the 1st memory address of an object’s contiguous memory block.

[ProgrammingN00b]

Yes, that is the weird part, because C or C++ does not do that …

[GoToLoop]

Can you explain how C/C++ variable assigning is different than Java’s then?

[ProgrammingN00b]

Variable1 = 5; Variable2 = 10;

Variable1 = Variable2;
//The value of Variable1 would now be 10

Variable2 = 20;
//Setting the new value of variable2 to 20

//Variable1 would still be 10 and not change as Variable2 gets changed


[GoToLoop]

That’s exactly what happens in Java too! So I dunno what’s your point.

int var1 = 5, var2 = 10;
println(var1, var2); // 5, 10

var1 = var2;
println(var1, var2); // 10, 10

var2 = 20;
println(var1, var2); // 10, 20

exit();

[ProgrammingN00b]

But in C++ this would copy the “value” no matter what type the variable is!
So even if it is a custom class / object …
Or a member variable of an object / class …

[GoToLoop]

@ProgrammingN00b

But in C++ this would copy the “value” no matter what type the variable is!

By “copy” you actually mean “clone”.

That is, rather than assigning a copy of the same value from right to left C/C++ would clone an object, thus generating a new value, which is then assigned to the left variable.

In Java cloning isn’t done automatically. We’d need to code a function for it.

[paulgoux]

Usually if i have to deal with copies, ill use something which can store an object usually an arraylist. I use one for the original and a second one for all copies.

Then i iterate through the first arraylist and based on the conditions im looking for ill code an appropriate logic statement and set an index object in the second arraylist or empty the arraylist and add the desired object.

Not necessarily as direct as in other languages but it works.

Im sure there might be better ways though.

[ProgrammingN00b]

Ok, I guess I will try to create a function to “clone” values from one variable to another …

(That’s what I get for saying “this processing stuff is easier then c++”, oh well …)

[ProgrammingN00b]

That is probably some good advice, but I don’t understand enough of this yet to fully comprehend it …

[ProgrammingN00b]

I just found this article:

Comparison of Java and C++

It esplains the differences between c++ and java.

[GoToLoop]

This is that wiki’s relevant part:

[ProgrammingN00b]

But it appears that that function variable.clone() does not exist in processing …

[GoToLoop]

Look again what’s stated on the wiki screenshot I’ve posted earlier:

// the Foo class must implement the Cloneable interface
//     for this code to compile

As I’ve warned you before we’ve gotta code our own clone() function.

Here’s an example of how to implement a clone() method within a class:

Functions argument

Or even better, use it as an actual full-fledged class, w/ constructors, fields & methods: // https://Discourse.Processing.org/t/functions-argument/11010/5 // GoToLoop (v1.1) (2019/May/09) final Pair pair = new Pair(5, -10); void setup() { println(pair); // [ 5, -10 ] println(pair.calc('y')); // [ -50, 540 ] println(pair.set(5, -10)); // [ 5, -10 ] println(pair.calc('u')); // [ 3, -2 ] println(pair.clone()); // [ 3, -2 ] exit(); } static final class…

[ProgrammingN00b]

I think found a better solution:
Something like “processing” but for c++!
https://openframeworks.cc/