mission-peace/interview · error · IllegalArgumentException

Cloning non directed graph

Error message

Cloning non directed graph

What it means

clone() only supports cloning directed graphs; it uses graph.isDirected as a precondition check. If a graph whose isDirected flag is false is passed, it throws IllegalArgumentException("Cloning non directed graph") because the clone routine builds a Graph<>(true) and assumes directed edge semantics.

Solutions

1. Construct the graph as directed (new Graph<>(true)) before cloning
2. If undirected cloning is needed, implement or use a separate clone routine for undirected graphs
3. Check graph.isDirected before calling and branch to the appropriate cloner

Example fix

// before
Graph<T> copy = cloner.clone(undirectedGraph);
// after
if (undirectedGraph.isDirected) {
    Graph<T> copy = cloner.clone(undirectedGraph);
} else {
    throw new UnsupportedOperationException("use undirected clone");
}

if (!graph.isDirected) {
    throw new UnsupportedOperationException("clone requires a directed graph");
}

boolean isClonable(Graph<T> g) { return g != null && g.isDirected; }

try {
    Graph<T> copy = cloner.clone(graph);
} catch (IllegalArgumentException e) {
    throw new IllegalStateException("undirected graph passed to directed clone", e);
}

When it happens

Trigger: Calling clone(graph) with a graph created via new Graph<>(false) or any undirected Graph instance.

Common situations: Passing a graph built by a different factory/constructor default, or reusing an undirected graph utility where a directed one was expected after an API change.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• No vertex in the graph
• Not same length input
• Duplicate date

AI-assisted analysis of mission-peace/interview@94be5deb0c (2026-09-08). Data as JSON: /api/errors/2bdef693a5ad2a97. Report an issue: GitHub.

Appendix: source

Thrown at src/com/interview/graph/CloneDirectedGraph.java:23

/**
 * Given a directed graph clone it in O(n) time where n is total number of edges
 * Test cases
 * Graph is directed/non directed
 * Graph has 0 edges
 * Graph has cycle
 * Graph is linear
 * Graph is dense
 * Graph is sparse
 */
public class CloneDirectedGraph<T> {

    public Graph<T> clone(Graph<T> graph){
        if(graph == null){
            return null;
        }
        if(!graph.isDirected){
            throw new IllegalArgumentException("Cloning non directed graph");
        }
        if(graph.getAllVertex().size() == 0){
            throw new IllegalArgumentException("No vertex in the graph");
        }
        Map<Vertex<T>,Vertex<T>> cloneMap = new HashMap<Vertex<T>,Vertex<T>>();
        for(Vertex<T> vertex : graph.getAllVertex()){
            clone(vertex,cloneMap);
        }
        Graph<T> clonedGraph = new Graph<>(true);
        for(Vertex<T> vertex : cloneMap.values()){
            clonedGraph.addVertex(vertex);
        }
        return clonedGraph;
    }
    
    private void clone(Vertex<T> origVertex,Map<Vertex<T>,Vertex<T>> cloneMap){
        Vertex<T> cloneVertex = null;
        if(cloneMap.containsKey(origVertex)){

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