Maps and Sets, why wont this work?

[jazzermonty]

Hello again folks

Ok, here is my problem:

I have a Map called results. This map holds a Character as it's key and a Set of type String as it's value. When I find the character (from another map, based on imaginery student grades) I want to put the name of that student into the corresponding set with the key matching the Character.

Here's my method

 public void collateResults()
   {      
      char grades[] = {'A', 'B', 'C', 'D', 'F', 'X'};
      Set<String> resultSet = new HashSet <String>();     
      for(int i = 0; i < grades.length; i++)
       {
          this.results.put(grades[i], resultSet);          
       } 
          
           Set<String> key = students.keySet();
           for (String theStudents : key)
           {
             Character aChar =  this.students.get(theStudents).getGrade();
             String aName = this.students.get(theStudents).getName();         
             Set<Character> keys = results.keySet();
             for(Character allGrades : keys)             
              {             
               if(allGrades.equals(aChar))
                  {                     
                   resultSet = this.results.get(aChar).add(aName);
                  }                 
               }
          }                   
   }

I've tested the if statement, and it is comparing the Character to the key correctly, however, when I then want to add the name (aName) to the corresponding set the method instead adds the name to ALL sets.

What's wrong?

Thanks

[JosAH]

      char grades[] = {'A', 'B', 'C', 'D', 'F', 'X'};
      Set<String> resultSet = new HashSet <String>();     
      for(int i = 0; i < grades.length; i++)
       {
          this.results.put(grades[i], resultSet);          
       }

This is where you go wrong, all the keys are associated with the same HashSet. Better make that:

      char grades[] = {'A', 'B', 'C', 'D', 'F', 'X'};
      for(int i = 0; i < grades.length; i++)
       {
          this.results.put(grades[i], new HashSet<String>());          
       }

kind regards,

Jos

[jazzermonty]

This is where you go wrong, all the keys are associated with the same HashSet. Better make that:

      char grades[] = {'A', 'B', 'C', 'D', 'F', 'X'};
      for(int i = 0; i < grades.length; i++)
       {
          this.results.put(grades[i], new HashSet<String>());          
       }

kind regards,

Jos

Jos, you are a star. Thank you sooooo much.

[JosAH]

Jos, you are a star. Thank you sooooo much.

Java is not like C++; C++ makes a copy of an object when you stick that object in a container; Java doesn't do anything 'behind your back', i.e. the language is way too simple to do such things.

kind regards,

Jos