Returns a list of nodes in a Java node. A parent node can have multiple child nodes

I'm trying to write java code to return a list of nodes in the tree

The node class is

class Node{
 String label;
 List<Node> children;
}

I'm trying this way But I can't understand how to write a loop to traverse

public List<Node> returnAllNodes(Node node){
    List<Node> listOfNodes = 
        new ArrayList<Node>();
    boolean iterationCompleted = false;
    if(node==null){
        return null;
    }
    while(!iterationCompleted){
    if(node.getChildren()==null){
        listOfNodes.add(node);
                    break;    
    }
            else{
               //
            }
    }
    return null;
    //return traverseAndReturnAllNodes(node.getChildren().get(0));
}

Please help.

Solution

If you determine that the structure is a tree (nodes cannot have multiple parent nodes), the nodes are listed in depth priority order:

public static List<Node> returnAllNodes(Node node){
    List<Node> listOfNodes = new ArrayList<Node>();
    addAllNodes(node,listOfNodes);
    return listOfNodes;
}

private static void addAllNodes(Node node,List<Node> listOfNodes) {
    if (node != null) {
        listOfNodes.add(node);
        List<Node> children = node.getChildren();
        if (children != null) {
            for (Node child: children) {
                addAllNodes(child,listOfNodes);
            }
        }
    }
}

If a node can have multiple parent nodes, change the first line of addallnodes to:

if (node != null && !listOfNodes.contains(node)) {

The breadth first algorithm is as follows:

public static List<Node> returnAllNodes(Node node){
    List<Node> listOfNodes = new ArrayList<Node>();
    if (node != null) {
        listOfNodes.add(node);
        for(int i = 0; i < listOfNodes.size(); ++i) {
            Node n = listOfNodes.get(i);
            List<Node> children = n.getChildren();
            if (children != null) {
                for (Node child: children) {
                    if (!listOfNodes.contains(child)) {
                        listOfNodes.add(child);
                    }
                }
            }
        }
    }
    return listOfNodes;
}