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Link Intersystems Commons Graph (lis-commons-graph) is a collection of reusable software components that provide support for graph and tree related programming tasks, such as models and search algorithms.

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package com.link_intersystems.graph.tree;

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Stack;
import java.util.stream.Stream;

/**
 * @author René Link {@literal }
 */
public class DepthFirstTreeModelIterable extends AbstractTreeModelIterable {

    public DepthFirstTreeModelIterable(TreeModel treeModel, T rootElement) {
        super(treeModel, rootElement);
    }

    @Override
    protected Iterator createIterator(TreeModel treeModel, T rootElement) {
        Stack stack = new Stack<>();
        stack.push(rootElement);

        return new Iterator() {

            @Override
            public boolean hasNext() {
                return !stack.isEmpty();
            }

            @Override
            public T next() {
                if (!hasNext()) {
                    throw new NoSuchElementException();
                }

                T current = stack.pop();

                Stream children = treeModel.getChildren(current);
                int headIndex = stack.size();
                children.forEach(c -> stack.add(headIndex, c));

                return current;
            }
        };
    }
}