Question

I have a tree that consists of different type of objects for example

   Tree
    |  \
  apple  cat
    |  \
  dog  grass
        |   \
       door something

For example I can access the object something using Tree.getApple().getGrass().getSomething() where on every getter I have to check if the node exists. The problem is that the structure I use is pretty big and I want to have a utility class to speed this up.

I want only given the name of the object to be able to extract it from the structure. For example to have a method to which after I give Something.class as an argument to traverse the structure, return the object if it exists and return null otherwise. (I cannot have multiple occurrences of one class in the structure, i.e. I can have only one apple object)

Is that possible? What can I use to implement it?

Answer 1

Implement a visitor that traverses the three and implement the filter in the visitor.

Roughly:

    public class LeafSearching {

    private final Class typeToFind;

    private Object result;

    public LeafSearching(Class typeToFind) {
        this.typeToFind = typeToFind;
    }

    public void visit(Node node) {
        if (typeToFind.isAssignableFrom(node.getClass())){
            result = node;
            return;
        }

        for (Node child : node.getChildren()) {
            child.accept(this);
        }
    }
}

interface Node {

    boolean hasChildren();

    List<Node> getChildren();

    void accept(LeafSearching ls);
}

class Apple implements Node {
    //...
}

class Cat implements Node {
    // ...
}

class TreeRoot implements Node {

    private Apple apple;

    private Cat cat;

    public Apple getApple() {
        return apple;
    }

    public Cat getCat() {
        return cat;
    }

    @Override
    public boolean hasChildren() {
        return false;
    }

    @Override
    public List<Node> getChildren() {
        final List<Node> children = new ArrayList<Node>;

        if (getApple() != null) {
            children.add(this.apple);
        }

        if (getCat() != null) {
            children.add(this.cat);
        }

        return children;
    }

    public void accept(LeafSearching ls) {
        ls.visit(this);
    }
}