Question

Let’s say I have an object of each class below, and I put each object in a hashmap where IDnumber is the key in both maps.

class1 {
 int IDNumber = 123;  //same person as class2
 String name = John;
 String company = Intel;

 class2 { 
 int IDNumber = 123;  //same person as class1
 int income = 500;
 int workYears = 3;
 } 

HashMap<Integer, class1> one = new Hashmap<Integer, class1>();
HashMap<Integer, class2> two = new HashMap<Integer, class2>();

Now, how can I mash these two HashMaps into a third HashMap so that I can have the key IDnumber, and the values name, company, income, and workyears?

Answer 1

You can not do that. You have two different classes, and java is not going to auto-magically make them one.

You could create a new third class to merge the info:

public Class3 {

   public Class3(Class1 class1, Class2 class2){
       //pull the info you want from each into variables in this class
   }
}

Then loop through your map to get the entries, creating new Class3 instance for each and place them in a new HashMap<Integer, Class3>.

//gets the keys from the hashmap
Set<Integer> keys = one.keySet();
//merge the keys from the second hashmap
keys.addAll(two.keySet());
//new hashmap
Map<Integer, Class3> newMap = new HashMap<Integer, Class3>();
for (Integer key : keys){
     //create new instance and place it in the map
     newMap.put(key, new Class3(one.get(key), two.get(key));
}