netbeans – Why do I get an "AWT-EventQueue-0" java.lang.NullPointerException?

I'm trying to make a program in netbeans that makes simplex tables, but when you click on the "calculate" button and show results, you do not take any action and send an error in the line:

    for (int j = 0; j <(variables + constraints + 1); j ++) {
               Matrix[i][j]    = Double.parseDouble (jTable1.getValueAt (i, j + 1) .toString ());
            }

And the code is:

public class Simplex extends javax.swing.JFrame {
double Matrix[][];
int restrictions = 0, variables = 0, iter = 0, iteration = 0;
Object array[];
Object LabelX[], Etiquette[];
public void NewTable (int Row, int Column) {
    double pivot = Matrix[Fila][Columna], temp = 0;
    for (int i = 0; i <constraints + variables + 1; i ++) {
        Matrix[Fila][i]    = Matrix[Fila][i]    / pivot;
    }
    for (int i = 0; i <constraints + 1; i ++) {
        temp = Matrix[i][Columna];
        for (int j = 0; j <variables + constraints + 1; j ++) {
            if (i! = Row) {
                Matrix[i][j]    = Matrix[i][j]    - temp * Matrix[Fila][j];
            } else {
                break;
            }
        }
    }
}
    private void solucionActionPerformed (java.awt.event.ActionEvent evt) {
    DefaultTableModel modelSolution = new DefaultTableModel ();
        Matrix = new double[restricciones + 1][restricciones + variables + 1];
        for (int i = 0; i <(constraints + 1); i ++) {
            for (int j = 0; j <(constraints + variables + 1); j ++) {
               Matrix[i][j]    = Double.parseDouble (jTable1.getValueAt (i, j + 1) .toString ());
            }
        }
        while (CheckResult ()! = true) {
            Etiquette[FilaPivote()] = LabelX[ColumnaPivote()];
            NewTable (PivotTable (), PivotTable ());
            modelSolution.setColumnCount (constraints + variables + 2);
            modelSolution.setRowCount (restrictions + 1);
            modelSolution.setColumnIdentifiers (array);
            for (int i = 0; i <(constraints + 1); i ++) {
                modelSolution.setValueAt (LabelY[i], i, 0);
                for (int j = 0; j <(constraints + variables + 1); j ++) {
                    modelSolucion.setValueAt (Matrix[i][j], i, j + 1);
                }
            }
            s_table.setModel (modelSolution);
            iteration ++;
        }
        solucion.setEnabled (false);
        itr.setEnabled (true);
}