refact: rewrite static classes to increase test coverage (#797)

src/main/java/neqsim/MathLib/generalMath/TDMAsolve.java

@@ -14,7 +14,13 @@
  * @author Even Solbraa
  * @version $Id: $Id
  */
-public class TDMAsolve {
+public final class TDMAsolve {
+
+  /**
+   * Dummy constructor, not for use. Class is to be considered static.
+   */
+  private TDMAsolve() {}
+
   /**
    * <p>
    * solve.
@@ -26,11 +32,11 @@ public class TDMAsolve {
    * @param r an array of {@link double} objects
    * @return an array of {@link double} objects
    */
-  public static double[] solve(double a[], double b[], double c[], double r[]) {
+  public static double[] solve(double[] a, double[] b, double[] c, double[] r) {
     int length = a.length;
     double[] u = new double[length];
     double bet = 0;
-    double gam[] = new double[length];
+    double[] gam = new double[length];
 
     bet = b[0];
     u[0] = r[0] / bet;

src/main/java/neqsim/MathLib/nonLinearSolver/NumericalDerivative.java

@@ -17,21 +17,19 @@
  * @author Even Solbraa
  * @version $Id: $Id
  */
-public class NumericalDerivative implements java.io.Serializable {
+public final class NumericalDerivative implements java.io.Serializable {
   private static final long serialVersionUID = 1000;
 
-  final static double CON = 1.4;
-  final static double CON2 = CON * CON;
-  final static double BIG = 1 * Math.pow(10, 30);
-  final static int NTAB = 100;
-  final static double SAFE = 2;
+  static final double CON = 1.4;
+  static final double CON2 = CON * CON;
+  static final double BIG = 1 * Math.pow(10, 30);
+  static final int NTAB = 100;
+  static final double SAFE = 2;
 
   /**
-   * <p>
-   * Constructor for NumericalDerivative.
-   * </p>
+   * Dummy constructor, not for use. Class is to be considered static.
    */
-  public NumericalDerivative() {}
+  private NumericalDerivative() {}
 
   /**
    * <p>

src/main/java/neqsim/chemicalReactions/chemicalReaction/ChemicalReactionFactory.java

@@ -18,15 +18,13 @@
  * @author ESOL
  * @version $Id: $Id
  */
-public class ChemicalReactionFactory {
+public final class ChemicalReactionFactory {
   static Logger logger = LogManager.getLogger(ChemicalReactionFactory.class);
 
   /**
-   * <p>
-   * Constructor for ChemicalReactionFactory.
-   * </p>
+   * Dummy constructor, not for use. Class is to be considered static.
    */
-  public ChemicalReactionFactory() {}
+  private ChemicalReactionFactory() {}
 
   /**
    * <p>

src/main/java/neqsim/statistics/parameterFitting/NumericalDerivative.java

@@ -14,21 +14,19 @@
  * @author Even Solbraa
  * @version $Id: $Id
  */
-public class NumericalDerivative implements java.io.Serializable {
+public final class NumericalDerivative implements java.io.Serializable {
   private static final long serialVersionUID = 1000;
 
-  final static double CON = 1.4;
-  final static double CON2 = CON * CON;
-  final static double BIG = 1.0e30;
-  final static int NTAB = 10;
-  final static double SAFE = 2.0;
+  static final double CON = 1.4;
+  static final double CON2 = CON * CON;
+  static final double BIG = 1.0e30;
+  static final int NTAB = 10;
+  static final double SAFE = 2.0;
 
   /**
-   * <p>
-   * Constructor for NumericalDerivative.
-   * </p>
+   * Dummy constructor, not for use. Class is to be considered static.
    */
-  public NumericalDerivative() {}
+  private NumericalDerivative() {}
 
   /**
    * <p>
@@ -42,15 +40,16 @@ public NumericalDerivative() {}
    */
   public static double calcDerivative(StatisticsBaseClass system, int sampleNumber,
       int parameterNumber) {
-    double errt, fac, hh, ans, err;
+    double errt;
+    double fac;
+    double hh;
     double h = Math.abs(system.getSampleSet().getSample(sampleNumber).getFunction()
         .getFittingParams(parameterNumber)) / 1.0e3;
     if (h == 0.0) {
       System.out.println("h must be larger than 0!");
       System.out.println("setting it to 1.0e-10");
       h = 1.0e-10;
     }
-    double[][] a = new double[NTAB][NTAB];
 
     hh = h;
     // System.out.println("hh " + hh);
@@ -65,9 +64,10 @@ public static double calcDerivative(StatisticsBaseClass system, int sampleNumber
     system.getSampleSet().getSample(sampleNumber).getFunction().setFittingParams(parameterNumber,
         oldFittingParam1);
 
+    double[][] a = new double[NTAB][NTAB];
     a[0][0] = (val1 - val2) / (2.0 * hh);
-    ans = a[0][0];
-    err = BIG;
+    double ans = a[0][0];
+    double err = BIG;
 
     for (int i = 1; i <= 0 * NTAB - 1; i++) {
       hh /= CON;

src/main/java/neqsim/thermo/FluidCreator.java

@@ -3,24 +3,26 @@
 import neqsim.thermo.system.SystemInterface;
 
 /**
- * Used to generate fluids of type SystemInterface
- * <p>
- * FluidCreator class.
- * </p>
+ * Used to generate fluids of type SystemInterface.
  *
  * @author esol
  * @version $Id: $Id
  */
-public class FluidCreator {
-  /** Constant <code>hasWater=false</code> */
+public final class FluidCreator {
+  /** Constant <code>hasWater=false</code>. */
   public static boolean hasWater = false;
-  /** Constant <code>autoSelectModel=false</code> */
+  /** Constant <code>autoSelectModel=false</code>. */
   public static boolean autoSelectModel = false;
-  /** Constant <code>thermoModel="srk"</code> */
+  /** Constant <code>thermoModel="srk"</code>. */
   public static String thermoModel = "srk";
-  /** Constant <code>thermoMixingRule="classic"</code> */
+  /** Constant <code>thermoMixingRule="classic"</code>. */
   public static String thermoMixingRule = "classic";
-
+
+  /**
+   * Dummy constructor, not for use. Class is to be considered static.
+   */
+  private FluidCreator() {}
+
   /**
    * Create SystemInterface.
    *

src/test/java/neqsim/PVTsimulation/simulation/DifferentialLiberationTest.java

@@ -8,7 +8,7 @@ public class DifferentialLiberationTest {
 
   @Test
   void testRunCalc() {
-    SystemInterface tempSystem = new FluidCreator().create("black oil");
+    SystemInterface tempSystem = FluidCreator.create("black oil");
 
     DifferentialLiberation CVDsim = new DifferentialLiberation(tempSystem);
     CVDsim.setPressures(new double[] {300.0, 250.0, 200.0, 150.0, 100.0, 70.0, 50.0, 30.0, 10.0});