System.arraycopy() any clue?

Programming Questions

cidelab

in Programming Questions • 1 year ago

hello to all

I'm passing an array(char[][]) into a method. I'm using the arraycopy() to make a copy of the array and avoid modify the array outside of the class. but I can't get it.

please any help will be amazing.

thanks in advance

public char[][] GenrMutation(char[][] pop, float ChroPercent)
{
SelectChromosomes(pop);
int chroCant = (int)(pop[0].length * ChroPercent);
if(chroCant == 0){ chroCant = 1;}
char[][] mutatedPop = new char[pop.length][];
System.arraycopy(pop, 0, mutatedPop, 0, pop.length);
char rndChar; //random Character to replace
int pointer; //random pointer, for the index
for(int i = 0; i < cant; ++i) //the loop for the pop
{
for(int j = 0; j < chroCant; ++j) //the loop for the chro
{
rndChar = RandomChar();
pointer = new Random().nextInt(mutatedPop[i].length);
mutatedPop[arrIndex[i]][pointer] = rndChar;
}
}
return mutatedPop;
}

and in the main, this is how I'm calling the function.

also I tryed using the clone() function. but it did not work.

import processing.core.*;

public class Main {

static PApplet mirrorApplet;

public static void main(String[] args)

{

char[][] myCharPop;

@SuppressWarnings("unused")

char[][] mutatedPop;

MGenrPopulation charPop = new MGenrPopulation();

myCharPop = charPop.CharPopulation(5, 10);

MMutation mutation = new MMutation(mirrorApplet, (float)0.4);

mutatedPop = mutation.GenrMutation(myCharPop, (float)0.3);

}

}

Replies(4)

quarks

Re: System.arraycopy() any clue?

1 year ago

The problem is that a 2D array is treated as an arrray of 1D arrays so the lines

char[][] mutatedPop = new char[pop.length][];
System.arraycopy(pop, 0, mutatedPop, 0, pop.length);

does not actually copy the data it copies the array references so changing the data in the new array is still changing the data in the old array. The solution is copy the 1D arrays as well.

char[][] mutatedPop = new char[pop.length][];
for(int i = 0; i < pop.length; i++){
mutatedPop[i] = new char[pop[i].length];
System.arraycopy(pop[i], 0, mutatedPop[i], 0, pop[i].length);
}

Replace lines 8 & 9 with the above code.

BTW I have not tested the code but I can't see any syntax errors.

quarks

Re: System.arraycopy() any clue?

1 year ago

I have also moved this to Programming Questions. This maybe part of a library or tool you are developing but as described it is a Java programming problem.

cidelab

Re: System.arraycopy() any clue?

1 year ago

thanks a lot quad.

perfect!

but when I call this method from processing, should I have to do the same with the array and use the function arrayCopy()?

thanks in advance

kind regards.

quarks

Re: System.arraycopy() any clue?

1 year ago

This is the source code for Processing's arrayCopy() method

/**
* Convenience method for arraycopy().
* Identical to <CODE>arraycopy(src, 0, dst, 0, length);</CODE>
*/
static public void arrayCopy(Object src, Object dst, int length) {
System.arraycopy(src, 0, dst, 0, length);
}

as you can see it simply calls the System.arraycopy() method so both methods do the same thing so take your pick it won't make any real difference this will also work

char[][] mutatedPop = new char[pop.length][];
for(int i = 0; i < pop.length; i++){
mutatedPop[i] = new char[pop[i].length];
PApplet.arrayCopy(pop[i], 0, mutatedPop[i], 0, pop[i].length);
}

or even this will work if the code is in the pde file

char[][] mutatedPop = new char[pop.length][];
for(int i = 0; i < pop.length; i++){
mutatedPop[i] = new char[pop[i].length];
arrayCopy(pop[i], 0, mutatedPop[i], 0, pop[i].length);
}