TheAlgorithms/Java · error · IllegalArgumentException

Edges list must not be null or empty

Error message

Edges list must not be null or empty

What it means

Thrown by the BoruvkaAlgorithm.Graph constructor when the `edges` list is null or empty. Boruvka's algorithm builds a minimum spanning tree from edges, so an empty edge set is meaningless and the constructor refuses it; null is treated identically to guard against uninitialized inputs.

Source

Thrown at src/main/java/com/thealgorithms/datastructures/graphs/BoruvkaAlgorithm.java:50

    /**
     * Represents the graph
     */
    static class Graph {
        final int vertex;
        final List<Edge> edges;

        /**
         * Constructor for the graph
         *
         * @param vertex number of vertices
         * @param edges  list of edges
         */
        Graph(final int vertex, final List<Edge> edges) {
            if (vertex < 0) {
                throw new IllegalArgumentException("Number of vertices must be positive");
            }
            if (edges == null || edges.isEmpty()) {
                throw new IllegalArgumentException("Edges list must not be null or empty");
            }
            for (final var edge : edges) {
                checkEdgeVertices(edge.src, vertex);
                checkEdgeVertices(edge.dest, vertex);
            }

            this.vertex = vertex;
            this.edges = edges;
        }
    }

    /**
     * Represents a subset for Union-Find operations
     */
    private static class Component {
        int parent;
        int rank;

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Ensure the edges list is populated before construction; load/generate edges first
2. If an empty graph is legitimately possible in your flow, short-circuit before constructing (Boruvka needs >=1 edge)
3. Replace null with an explicit non-empty list or fail earlier at the data-source step

Example fix

// before
Graph g = new BoruvkaAlgorithm.Graph(n, edges);
// after
if (edges == null || edges.isEmpty()) {
    throw new IllegalStateException("no edges loaded");
}
Graph g = new BoruvkaAlgorithm.Graph(n, edges);

if (edges == null || edges.isEmpty()) {
    throw new IllegalArgumentException("edges must be non-empty");
}

try {
    new BoruvkaAlgorithm.Graph(v, edges);
} catch (IllegalArgumentException e) {
    // handle empty/null edges
}

When it happens

Trigger: Constructing the Graph with `null` for edges, `Collections.emptyList()`, or a list filtered down to zero elements (e.g. `edges.stream().filter(...).toList()`).

Common situations: Loading edge data from a file/network that returned nothing; a filter that removes all edges; forgetting to populate the list before constructing the graph.

Related errors

• Adjacency list must not be null
• Adjacency list must not contain null sets
• Capacity matrix must not be null or empty
• IPv4 address is empty.
• Input cannot be null or empty

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/c385131273156cc1. Report an issue: GitHub.