>From: "stephan opitz" <[EMAIL PROTECTED]>
>
> problem is the structure.
>
> if i have an object containing an id and a parentId (which is null, or
> linking to another object -> the parent one)
>
> if i get a list from db how is it possible to build up the structure
> for the tree2
>
> i tried hashmap or recursive algorithm, but nothing with much success...
>
> any ideas
>
You might consider the following code snippet.
public class TreeBacker {
public TreeNode findNode(TreeNode root, Integer sarg) {
Integer id = root.getDescription() == null ? null : new
Integer(root.getDescription());
if (compare(id, sarg) == 0) {
return root;
}
Iterator ci = root.getChildren().iterator();
while (ci.hasNext()) {
TreeNode found = findNode((TreeNode) ci.next(), sarg);
if (found != null)
return found;
}
return null;
}
public TreeNode getTreeData() {
TreeNode root = new TreeNodeBase("root", null, false);
TreeNode current = root; // current root
Collection dbRows = getDBRows();
Iterator di = dbRows.iterator();
while (di.hasNext()) {
MyVO vo = (MyVO) di.next();
Integer id = current.getDescription() == null ? null : new
Integer(current.getDescription());
int order = compare(id, vo.getParent());
if (order != 0) {
current = findNode(root, vo.getParent());
// if current is null you have an orphaned node
}
String type = vo.getParent() == null ? null :
vo.getParent().toString();
String desc = vo.getId() == null ? null : vo.getId().toString();
current.getChildren().add(new TreeNodeBase(type, desc, false));
}
return root;
}
public Collection getDBRows() {
// select parent, id from table order by parent, id
// null, 1
// null, 2
// null, 3
// 1, 4
// 1, 5
// 2, 6
// 2, 7
// 3, 8
// 3, 9
// 9, 10
// 9, 11
Set sortedList = new TreeSet();
sortedList.add(new MyVO(null, new Integer(1)));
sortedList.add(new MyVO(new Integer(1), new Integer(4)));
sortedList.add(new MyVO(new Integer(1), new Integer(5)));
sortedList.add(new MyVO(null, new Integer(2)));
sortedList.add(new MyVO(new Integer(2), new Integer(6)));
sortedList.add(new MyVO(new Integer(2), new Integer(7)));
sortedList.add(new MyVO(null, new Integer(3)));
sortedList.add(new MyVO(new Integer(3), new Integer(8)));
sortedList.add(new MyVO(new Integer(3), new Integer(9)));
sortedList.add(new MyVO(new Integer(9), new Integer(10)));
sortedList.add(new MyVO(new Integer(9), new Integer(11)));
return sortedList;
}
class MyVO implements Comparable {
private Integer parent = null;
private Integer id = null;
public MyVO(Integer parent, Integer id) {
this.parent = parent;
this.id = id;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public Integer getParent() {
return parent;
}
public void setParent(Integer parent) {
this.parent = parent;
}
public int compareTo(Object obj) {
MyVO vo = (MyVO) obj;
int order = compare(parent, vo.parent);
if (order == 0)
order = compare(id, vo.id);
return order;
}
}
public static int compare(Integer col1, Integer col2) {
if ((col1 == null) && (col2 == null))
return 0;
else if ((col1 == null) && (col2 != null))
return -1;
else if ((col2 == null) && (col1 != null))
return 1;
else
return ((Comparable) col1).compareTo(col2);
}
public static void main(String[] args) {
TreeBacker backer = new TreeBacker();
TreeNode root = backer.getTreeData();
}
}
> stephan
Gary
