TheAlgorithms/Java · error · IllegalArgumentException

Node index out of bounds

Error message

Node index out of bounds

What it means

Thrown by PageRank.getPageRank when the requested node is outside [1, nodeCount]. Nodes are 1-indexed in this API: node 1 is the first and node nodeCount is the last. Requesting node 0, a negative node, or a node greater than nodeCount is rejected before indexing the internal PageRank array.

Source

Thrown at src/main/java/com/thealgorithms/others/PageRank.java:121

     * @param matrix the adjacency matrix (1-indexed)
     */
    public void setAdjacencyMatrix(int[][] matrix) {
        for (int i = 1; i <= nodeCount; i++) {
            for (int j = 1; j <= nodeCount; j++) {
                setEdge(i, j, matrix[i][j]);
            }
        }
    }

    /**
     * Gets the PageRank value for a specific node
     *
     * @param node the node index (1-indexed)
     * @return the PageRank value
     */
    public double getPageRank(int node) {
        if (node < 1 || node > nodeCount) {
            throw new IllegalArgumentException("Node index out of bounds");
        }
        return pageRankValues[node];
    }

    /**
     * Gets all PageRank values
     *
     * @return array of PageRank values (1-indexed)
     */
    public double[] getAllPageRanks() {
        return pageRankValues.clone();
    }

    /**
     * Calculates PageRank using the default damping factor and iterations
     *
     * @param totalNodes the total number of nodes
     * @return array of PageRank values

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Use 1-based indices: iterate node from 1 to nodeCount inclusive.
2. If you hold 0-based indices, add 1 before calling getPageRank.
3. Verify nodeCount matches the graph size you expect before querying.
4. Clamp/validate external indices against [1, nodeCount] at the boundary.

Example fix

// before
for (int i = 0; i < nodeCount; i++) {
    double pr = pageRank.getPageRank(i); // i==0 throws
}

// after
for (int i = 1; i <= nodeCount; i++) {
    double pr = pageRank.getPageRank(i);
}

public static int toOneBased(int zeroBasedIndex, int nodeCount) {
    if (zeroBasedIndex < 0 || zeroBasedIndex >= nodeCount) {
        throw new IllegalArgumentException("index out of range");
    }
    return zeroBasedIndex + 1;
}
// usage:
double pr = pageRank.getPageRank(toOneBased(i, nodeCount));

public static boolean isValidNodeQuery(int node, int nodeCount) {
    return node >= 1 && node <= nodeCount;
}

try {
    value = pageRank.getPageRank(node);
} catch (IllegalArgumentException e) {
    // node is 1-indexed; if you passed a 0-based index, add 1 and retry
    throw e;
}

When it happens

Trigger: Calling getPageRank(node) with node < 1, node > nodeCount, or node == 0 (a common 0-based-index mistake).

Common situations: Treating the API as 0-indexed when it is 1-indexed; iterating 0..nodeCount-1 instead of 1..nodeCount; off-by-one after construction with a smaller nodeCount than expected.

Related errors

• Position must be between 0 and {array.length}
• Position must be between 0 and + (array.length - 1)
• Number of nodes must be between 1 and + MAX_NODES
• Total nodes must be between 1 and + MAX_NODES
• Damping factor must be between 0 and 1

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/77b92546fc6f15f4. Report an issue: GitHub.