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HashMaps and parent/child relationships
Posted on 2002-04-30
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
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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3 Comments
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.
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.
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
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
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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