Question

I have tree like following example, where every leaf is object.

[1]
 |--[2]
 |   |--[3]
 |   |--[4]
 |       |--[5]
 |--[6]

Class structure is:

public class Node {
    private Integer id;
    private List<Node> children;
    public Integer getId()
    {
        return id;
    }
    public void setId(Integer id)
    {
        this.id = id;
    }
    public List<Node> getChildren()
    {
        return children;
    }
    public void setChildren(List<Node> children)
    {
        this.children = children;
    }
}

If leaf 3 is selected, then breadcrumbs are 1 2 3. How can I create breadcrumbs from this tree? I know how I can recursively create tree, but I don’t know how I can select correct leafs to breadcrumbs.

Answer 1

You need a parent pointer in the children. When you add children, the parent node can set the children’s parent pointer to itself.

public class Node {
    private Integer id;
    private Node parent;
    private List<Node> children;
    public Integer getId()
    {
        return id;
    }
    public void setId(Integer id)
    {
        this.id = id;
    }
    public List<Node> getChildren()
    {
        return children;
    }
    public void setChildren(List<Node> children)
    {
        this.children = children;
        for (Node child : children) {
            child.parent = this;
        }
    }
    public Node getParent() {
        return parent;
    }
}

You can then easily use this to build your breadcrumbs from a selected leaf node.