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HashMaps and parent/child relationships

Posted on 2002-04-30
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Last Modified: 2012-05-04
I need to create a parent to child relationship of my records and would like to use hashmaps to store the data and then a TreeSet/Iterator to get the ordered value

The records are as follows and come in random order:

Record 1: Parent 1; Child 2
Record 2: Parent 2; Child 1
Record 3: Parent 1; Child 1
Record 4: Parent 3; Child 1

The output i'm trying to accomplish is:

Parent 1
     Child 1
     Child 2
Parent 2
     Child 1
Parent 3
     Child 1


I can easily fill the hash maps but can't figure out how to relate the children.

Thanks in advance.  Let me know if more clarification is needed.

Dave
 
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Question by:mred_mred
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Accepted Solution

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yoren earned 75 total points
ID: 6982462
One way to do this would be to create a hashmap of {Parent} --> {SortedSet of children}. You can also have a separate SortedSet of parents or even store them in the hashmap. Here's how you'd add a child:

SortedSet parents = (SortedSet) map.get("root");
Parent p1 = (Parent) parents.first();
SortedSet children = (SortedSet) map.get(p1);
if (children == null) {
  children = new TreeSet();
  map.put(p1,children);
}
children.add(new Child("Child 1"));

To get your output, just iterate through the parents; for each parent, iterate through the SortedSet of children.

Alternatively, and especially if you need more than one level of parent to child relationships, consider creating a Node class which has as a field a SortedSet of children.

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Author Comment

by:mred_mred
ID: 6983835
this definitely answered my question and i did seem to figure it out while waiting.  thanks for the quick response.

i do have more than one level.  where do i find the node class?  or do i create this my self?  class.child_node or something?  or is this a java class that i can use.

thanks
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LVL 7

Expert Comment

by:yoren
ID: 6983902
No, you'd have to create the Node class yourself. A Node could be a parent or a child, depending on if it has any children. Of course, this is assuming that parents and children have basically the same information. In the Node class you'll probably want a "name" field, a "children" field (which would be a SortedSet of other Nodes), and any other information pertinent to a node.
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