How do you iterate over a list that has a "parent/child/grandChild/etc."?
Sample data:
{ID, Parent ID}
Object parent = {1, 0};
Object childA = {2, 1};
Object childB = {3, 1};
Object grandChildA = {4, 3};
Object grandChildB = {5, 2};
And the list would be, {parent, childA, childB, grandChildA, grandChildB}
How do you iterate it by "roots"?
Sample output:
Thanks!
Sample data:
Constructor: SampleObject(int id,int parentId)
SampleObject parent = new SampleObject(1, 0);
SampleObject childA = new SampleObject(2, 1);
SampleObject childB = new SampleObject(3, 1);
SampleObject grandChildA = new SampleObject(4, 3);
SampleObject grandChildB = new SampleObject(5, 2);
I then placed the objects in an ArrayList: ArrayList testList
so, problem is, how to iterate over the list, so that the result would:
I do recommend a tree-like data structure, such as:
package com.stackoverflow.test;
import java.util.ArrayList;
import java.util.List;
public class TreeNode {
private String name = "";
private List<TreeNode> childNodes = new ArrayList<TreeNode>();
public TreeNode(final String name) {
this.name = name;
}
public String getName() {
return this.name;
}
public void add(final TreeNode child) {
childNodes.add(child);
}
public List<TreeNode> getChildren() {
return this.childNodes;
}
public static void main(String[] args) {
TreeNode parent = new TreeNode("Parent");
TreeNode childA = new TreeNode("ChildA");
childA.add(new TreeNode("GrandChildA"));
TreeNode childB = new TreeNode("ChildB");
childB.add(new TreeNode("GrandChildB"));
parent.add(childA);
parent.add(childB);
TreeNode.printRecursively(parent, 0);
}
private static void printRecursively(final TreeNode root, final int level) {
if (null != root && null != root.getChildren()) {
for (int i = 0; i < level; ++i) {
System.out.print(" ");
}
System.out.println(root.getName());
for (TreeNode child: root.getChildren()) {
TreeNode.printRecursively(child, level + 1);
}
}
}
}
Will print:
Parent
ChildA
GrandChildA
ChildB
GrandChildB
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