Trouble expanding and writing to array of objects

Processing Coding Questions
9

@WhiteSquire ,

Where are you getting a NullPointerException ?

Processing 4.3.4 will show you where. (Newer versions of Processing may not show this.)

@chrisir,

Adding this to your code example shows that the array is increasing and the logic for the small snippet shared with us seems correct:

void keyPressed()
  {
  setType();
  }

Some minimal code from my personal exploration of this topic to update ants in each cell:

Code < Click here to expand! 
// Code pieced together from various elements in this topic:
// https://discourse.processing.org/t/trouble-expanding-and-writing-to-array-of-objects/46750

// Some editions were made by glv in the exploration of this.

// A keypress (0 or 1) will increase the number of ants in each cell.
// This can be expanded to fill any number of cells.

int antsPerNest = 1;   // Initial
// int antAmt = 0;     // No longer be global, but per cell

int cellRows = 2;
int cellCols = 2;
int cellAmt = cellRows * cellCols;
int cellSize = 200;
cell[] c;

void setup() {
    c = new cell[cellAmt];
    println(c.length);

    // generate cells
    int i = 0;
    for (int y = 0; y < cellRows; y++) {
        for (int x = 0; x < cellCols; x++) {
            c[i] = new cell((x * cellSize) + (cellSize / 2),
                            (y * cellSize) + (cellSize / 2));
            // println(c[i].cellXY.x, c[i].cellXY.y);
            i++;
        }
    }
    println(i);
}

void draw() {
    // No drawing yet
}

class cell {
    PVector cellXY;
    ant[] antsInCell;      // Array to hold ants for this specific cell
    int currentAnts = 0;   // Counter for ants in this cell

    cell(float x, float y) {
        cellXY = new PVector(x, y);
        antsInCell = new ant[0]; // Initialize with an empty array
    }

    // setType() function moved into the cell class
    void setType() {
        antsInCell = (ant[]) expand(antsInCell, currentAnts + antsPerNest);

        // For examining output:
        println("Expanded:");
        debug(antsInCell);

        for (int j = currentAnts; j < antsInCell.length; j++) {
            // Spawn ants randomly within the cell's boundaries
            antsInCell[j] = new ant(
                random(cellXY.x - cellSize / 2, cellXY.x + cellSize / 2),
                random(cellXY.y - cellSize / 2, cellXY.y + cellSize / 2)
            );
            println("Added:", j, antsInCell[j].antXY.x, antsInCell[j].antXY.y);
        }
        currentAnts += antsPerNest;

        // For examining output:
        println("Updated:");
        debug(antsInCell);
    }
}

class ant {
    PVector antXY;

    ant(float x, float y) {
        antXY = new PVector(x, y);
    }
}

void keyPressed() 
  {
    if (key == '0') {
      println("Cell 0:");
        c[0].setType(); // Call setType on the first cell
        
    }
    else if (key == '1') {
        println("Cell 1:");
        c[1].setType(); // Call setType on the second cell

    }
    // Extend as needed...
  }

// Debug and examining objects for nulls
void debug(ant[] arr) {
    for (int n = 0; n < arr.length; n++) {
        if (arr[n] == null) {                           //object     
            println("null");
        } else {
            println(n, arr[n].antXY.x, arr[n].antXY.y); //element
        }
    }
    println();
}

The full code (not shared) displayed ants per cell and updated with keyPressed():

image
image422×459 9.08 KB

Sharing with the community!
I also had errors and NullPointerException along the way and sorted these out with some troubleshooting and experience.
There may be something in there of interest.

:)

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