Plouj

        class FunctionalDependency {                HashSet<String> LeftHandSide;                HashSet<String> RightHandSide;...                public boolean equals(Object obj) {                        boolean equal = false;                        if(this == obj)                                return true;                        if((obj == null) || (obj.getClass() != this.getClass()))                                return false;                        // object must be FunctionalDependency at this point                        FunctionalDependency FD = (FunctionalDependency)obj;                        if ( LeftHandSide.size() == FD.LeftHandSide.size() &&                                        RightHandSide.size() == FD.RightHandSide.size()) {                                for (String s : LeftHandSide) {                                        if (!FD.LeftHandSide.contains(s)) {                                                return false;                                        }                                }                                for (String s : RightHandSide) {                                        if (!FD.RightHandSide.contains(s)) {                                                return false;                                        }                                       }                                       return true;                        } else {                                return false;                        }                }        }...        class Relation {                HashSet<FunctionalDependency> FDs;...                public boolean add(FunctionalDependency fd) {                        return FDs.add(fd);                }...        }...                        Rinitial = new Relation();                        FunctionalDependency fd = new FunctionalDependency();                        String s;                        s = "A"; if (!fd.addLHS(s)) { System.out.println("add "+s+" failed"); }                        s = "B"; if (!fd.addLHS(s)) { System.out.println("add "+s+" failed1"); }                        s = "B"; if (!fd.addLHS(s)) { System.out.println("add "+s+" failed2"); }                        s = "C"; if (!fd.addLHS(s)) { System.out.println("add "+s+" failed"); }                        s = "D"; if (!fd.addRHS(s)) { System.out.println("add "+s+" failed"); }                        s = "E"; if (!fd.addRHS(s)) { System.out.println("add "+s+" failed"); }                        s = "F"; if (!fd.addRHS(s)) { System.out.println("add "+s+" failed"); }                        if (!Rinitial.add(fd)) {System.out.println("adding "+fd+" failed1");}                        if (!Rinitial.add(fd)) {System.out.println("adding "+fd+" failed2");}                        fd = new FunctionalDependency();                        s = "A"; if (!fd.addLHS(s)) { System.out.println("add "+s+" failed"); }                        s = "B"; if (!fd.addLHS(s)) { System.out.println("add "+s+" failed"); }                        s = "C"; if (!fd.addLHS(s)) { System.out.println("add "+s+" failed"); }                        s = "D"; if (!fd.addRHS(s)) { System.out.println("add "+s+" failed"); }                        s = "E"; if (!fd.addRHS(s)) { System.out.println("add "+s+" failed"); }                        s = "F"; if (!fd.addRHS(s)) { System.out.println("add "+s+" failed"); }                        if (!Rinitial.add(fd)) {System.out.println("adding "+fd+" failed3");}                        System.out.println(Rinitial);... prints:adding 'A', 'C', 'B' -> 'D', 'F', 'E' failed2['A', 'C', 'B' -> 'D', 'F', 'E'] ['A', 'C', 'B' -> 'D', 'F', 'E'].. should print something like:adding 'A', 'C', 'B' -> 'D', 'F', 'E' failed2adding 'A', 'C', 'B' -> 'D', 'F', 'E' failed3['A', 'C', 'B' -> 'D', 'F', 'E']