Question

I created an Matrix object (like the math Matrix, a 4×4 block of numbers for instance) and it works fine, can set row,col,variable just fine, but, I cant have more than one of the same object, I have it creating an ArrayList of a dozen Matrix objects, each with the three variables, but when I call changeVar(Matrix x,int variable) and refresh the printout of the matrix, it changes all of the numbers to what i changed the variable to. So it looks like its just creating the same instance over and over, and if you change one, it changes them all, am i missing anything obvious?

public class Matrices {

    private static int row, col, value, newRow, newCol;

    public Matrices(int row, int col, int value) {
        this.value = value;
        this.row = row;
        this.col = col;
    }

    public static void setRow(int row) {
        Matrices.row = row;
    }

    public static void setValue(int value) {
        Matrices.value = value;
    }

    public static void setCol(int col) {
        Matrices.col = col;
    }

    public static int getCol(Matrices x) {
        return col;
    }

    public static int getRow(Matrices x) {
        return row;
    }

    public static int getValue(Matrices x) {
        return value;
    }

    public static Matrices changeValue(Matrices x, int value) {
        newRow = getRow(x);
        newCol = getCol(x);
        return new Matrices(newRow, newCol, value);
    }
}

Answer 1

You are using static members. Static members are shared across all instances.

Don’t do that: remove the ‘static’ keyword.

I am surprised there were no warnings on the this.x = x lines…

Happy coding