Make *(one|zero) weights singletons

SynchronizedPDS/src/main/java/sync/pds/weights/SetDomainOne.java

@@ -24,6 +24,8 @@
 public class SetDomainOne implements SetDomain {
   @NonNull private static final SetDomainOne one = new SetDomainOne();
 
+  private SetDomainOne() {}
+
   public static Weight one() {
     return one;
   }

SynchronizedPDS/src/main/java/sync/pds/weights/SetDomainZero.java

@@ -27,6 +27,8 @@ public class SetDomainZero implements SetDomain {
 
   @NonNull private static final SetDomainZero zero = new SetDomainZero();
 
+  private SetDomainZero() {}
+
   @NonNull
   @Override
   public Weight extendWith(@NonNull Weight other) {

boomerangPDS/src/main/java/boomerang/weights/DataFlowPathWeightOne.java

@@ -27,7 +27,7 @@ public class DataFlowPathWeightOne implements DataFlowPathWeight {
 
   @NonNull private static final DataFlowPathWeightOne one = new DataFlowPathWeightOne();
 
-  public DataFlowPathWeightOne() {}
+  private DataFlowPathWeightOne() {}
 
   public static DataFlowPathWeightOne one() {
     return one;

boomerangPDS/src/main/java/boomerang/weights/MinDistanceWeightImpl.java

@@ -73,8 +73,7 @@ public boolean equals(Object obj) {
 
   @Override
   public String toString() {
-    final Weight one = new MinDistanceWeightOne();
-    return (this == one) ? "ONE " : " Distance: " + minDistance;
+    return "Distance: " + minDistance;
   }
 
   @Override

boomerangPDS/src/main/java/boomerang/weights/MinDistanceWeightOne.java

@@ -25,6 +25,8 @@ public static MinDistanceWeightOne one() {
     return one;
   }
 
+  private MinDistanceWeightOne() {}
+
   @NonNull
   @Override
   public Weight extendWith(@NonNull Weight o) {

boomerangPDS/src/main/java/boomerang/weights/PathConditionWeightOne.java

@@ -28,7 +28,7 @@ public class PathConditionWeightOne implements PathConditionWeight {
 
   @NonNull private static final PathConditionWeightOne one = new PathConditionWeightOne();
 
-  public PathConditionWeightOne(
+  private PathConditionWeightOne(
       Map<Statement, ConditionDomain> newIfs,
       Map<Val, ConditionDomain> newVals,
       Set<Val> newReturnVals,
@@ -52,17 +52,17 @@ public Map<Method, Statement> getCalleeToCallSite() {
     throw new IllegalStateException("PathConditionWeightOne.getCalleeToCallSite() - don't");
   }
 
-  public PathConditionWeightOne() {}
+  private PathConditionWeightOne() {}
 
   public static PathConditionWeightOne one() {
     return one;
   }
 
-  public PathConditionWeightOne(Statement callSite, Method callee) {
+  private PathConditionWeightOne(Statement callSite, Method callee) {
     this.getCalleeToCallSite().put(callee, callSite);
   }
 
-  public PathConditionWeightOne(Val returnVal) {
+  private PathConditionWeightOne(Val returnVal) {
     this.getReturnVals().add(returnVal);
   }
 

idealPDS/src/main/java/typestate/TransitionFunctionOne.java

@@ -31,7 +31,7 @@ public class TransitionFunctionOne implements TransitionFunction {
 
   @NonNull private static final TransitionFunctionOne one = new TransitionFunctionOne();
 
-  public TransitionFunctionOne() {}
+  private TransitionFunctionOne() {}
 
   public static TransitionFunctionOne one() {
     return one;
@@ -50,8 +50,9 @@ public Set<ControlFlowGraph.Edge> getStateChangeStatements() {
         "TransitionFunctionOne.getStateChangeStatements() - This should not happen!");
   }
 
+  @NonNull
   @Override
-  public Weight extendWith(Weight other) {
+  public Weight extendWith(@NonNull Weight other) {
     if (other.equals(one())) return this;
     if (this.equals(one())) return other;
     if (other.equals(zero()) || this.equals(zero())) {

idealPDS/src/main/java/typestate/TransitionFunctionZero.java

@@ -31,7 +31,7 @@ public class TransitionFunctionZero implements TransitionFunction {
 
   @NonNull private static final TransitionFunctionZero zero = new TransitionFunctionZero();
 
-  public TransitionFunctionZero() {}
+  private TransitionFunctionZero() {}
 
   @NonNull
   public static TransitionFunctionZero zero() {