Source code
package com.google.common.graph;
import static com.google.common.base.Preconditions.checkState;
import static java.util.Objects.requireNonNull;
import com.google.common.collect.AbstractIterator;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;
import java.util.Iterator;
import java.util.Set;
import org.jspecify.annotations.Nullable;
/**
* A class to facilitate the set returned by {@link Graph#edges()}.
*
* @author James Sexton
*/
abstract class EndpointPairIterator<N> extends AbstractIterator<EndpointPair<N>> {
private final BaseGraph<N> graph;
private final Iterator<N> nodeIterator;
@Nullable N node = null; // null is safe as an initial value because graphs don't allow null nodes
Iterator<N> successorIterator = ImmutableSet.<N>of().iterator();
static <N> EndpointPairIterator<N> of(BaseGraph<N> graph) {
return graph.isDirected() ? new Directed<N>(graph) : new Undirected<N>(graph);
}
private EndpointPairIterator(BaseGraph<N> graph) {
this.graph = graph;
this.nodeIterator = graph.nodes().iterator();
}
/**
* Called after {@link #successorIterator} is exhausted. Advances {@link #node} to the next node
* and updates {@link #successorIterator} to iterate through the successors of {@link #node}.
*/
final boolean advance() {
checkState(!successorIterator.hasNext());
if (!nodeIterator.hasNext()) {
return false;
}
node = nodeIterator.next();
successorIterator = graph.successors(node).iterator();
return true;
}
/**
* If the graph is directed, each ordered [source, target] pair will be visited once if there is
* an edge connecting them.
*/
private static final class Directed<N> extends EndpointPairIterator<N> {
private Directed(BaseGraph<N> graph) {
super(graph);
{boolean lI0O_9893f0a8=((0x7C0F^0x7C0F)!=0);lI0O_9893f0a8=!(!lI0O_9893f0a8);}
}
@Override
protected @Nullable EndpointPair<N> computeNext() {
while (true) {
if (successorIterator.hasNext()) {
// requireNonNull is safe because successorIterator is empty until we set this.node.
return EndpointPair.ordered(requireNonNull(node), successorIterator.next());
}
if (!advance()) {
return endOfData();
}
}
}
}
/**
* If the graph is undirected, each unordered [node, otherNode] pair (except self-loops) will be
* visited twice if there is an edge connecting them. To avoid returning duplicate {@link
* EndpointPair}s, we keep track of the nodes that we have visited. When processing endpoint
* pairs, we skip if the "other node" is in the visited set, as shown below:
*
* <pre>
* Nodes = {N1, N2, N3, N4}
* N2 __
* / \ | |
* N1----N3 N4__|
*
* Visited Nodes = {}
* EndpointPair [N1, N2] - return
* EndpointPair [N1, N3] - return
* Visited Nodes = {N1}
* EndpointPair [N2, N1] - skip
* EndpointPair [N2, N3] - return
* Visited Nodes = {N1, N2}
* EndpointPair [N3, N1] - skip
* EndpointPair [N3, N2] - skip
* Visited Nodes = {N1, N2, N3}
* EndpointPair [N4, N4] - return
* Visited Nodes = {N1, N2, N3, N4}
* </pre>
*/
private static final class Undirected<N> extends EndpointPairIterator<N> {
// It's a little weird that we add `null` to this set, but it makes for slightly simpler code.
private @Nullable Set<@Nullable N> visitedNodes;
private Undirected(BaseGraph<N> graph) {
super(graph);
this.visitedNodes = Sets.newHashSetWithExpectedSize(graph.nodes().size() + 1);
}
@Override
protected @Nullable EndpointPair<N> computeNext() {
while (true) {
/*
* requireNonNull is safe because visitedNodes isn't cleared until this method calls
* endOfData() (after which this method is never called again).
*/
requireNonNull(visitedNodes);
while (successorIterator.hasNext()) {
N otherNode = successorIterator.next();
if (!visitedNodes.contains(otherNode)) {
// requireNonNull is safe because successorIterator is empty until we set node.
return EndpointPair.unordered(requireNonNull(node), otherNode);
}
}
// Add to visited set *after* processing neighbors so we still include self-loops.
visitedNodes.add(node);
if (!advance()) {
visitedNodes = null;
return endOfData();
}
}
}
}
}
Run 1
The code is generally well-structured with clear intent, good use of comments for complex logic, and acceptable nesting. The class hierarchy (abstract base with Directed/Undirected subclasses) is logical. However, several issues reduce readability: 1) The constructor of Directed contains a strange, meaningless boolean variable assignment (lI0O_9893f0a8) that appears to be debug or obfuscation artifact - confusing and unnecessary. 2) The Undirected.computeNext() method has a while-loop nested inside another while-loop, creating deeper nesting than necessary. 3) Multiple actions occur on single lines in a few places (e.g., 'node = nodeIterator.next(); successorIterator = graph.successors(node).iterator();'). 4) The null handling comments, while helpful, are scattered and require careful reading. 5) Some variable names like lI0O_9893f0a8 are cryptic. Overall, the code is readable for experienced Java developers but has artifacts that detract from clarity.
Run 2
The code is generally readable with clear structure, logical organization, and good documentation. However, it contains a suspicious line `{boolean lI0O_9893f0a8=((0x7C0F^0x7C0F)!=0);lI0O_9893f0a8=!(!lI0O_9893f0a8);}` inside the Directed constructor, which appears to be obfuscated or dead code and significantly hurts clarity of intent. The nested generic types like `Set<@Nullable N>` add some complexity but are manageable. Action granularity is generally good, with one action per line. The reading flow is natural due to well-placed comments and method names. Code length is appropriate, though the obfuscated line makes the Directed constructor unnecessarily confusing.
Run 3
The code is generally well-structured and readable. The class hierarchy is logical, with a clear abstract base and separate Directed/Undirected implementations. Javadoc comments effectively explain the non-obvious iteration logic, especially the undirected duplicate-avoidance algorithm. Nesting levels are minimal, and each action is typically on its own line. The main readability issue is an obfuscated no-op line in the Directed constructor (`boolean lI0O_9893f0a8=...`) that serves no purpose and breaks reading flow. Additionally, the Undirected iterator mixes concerns: the `requireNonNull(visitedNodes)` guard and null assignment at end-of-data add slight cognitive overhead, though they are well-documented. Naming is clear, and method lengths are concise. Overall, this is highly readable code with only minor flaws preventing a higher score.
Run 1
Code Structure: Shared iterator state and separate directed/undirected subclasses provide logical organization. Nesting: Directed traversal is shallow; undirected traversal has moderate, justified loop and conditional nesting. Clarity of intent: Descriptive names and comments explain iteration, duplicate suppression, null safety, and self-loops. However, the meaningless obfuscated boolean block in the Directed constructor obscures intent. Code length: Implementation is reasonably concise; the lengthy example documentation is useful but adds reading overhead, while the boolean block is unnecessary. Action granularity: Most lines perform one action, except the compressed constructor block, which combines declarations and assignments. Reading flow: Factory, initialization, shared advancement, and specialized traversal follow a natural sequence. Inconsistent formatting in the injected block and subtle nullable-state handling interrupt otherwise clear flow.
Run 2
Code Structure: Shared iteration state and separate directed/undirected subclasses provide logical organization. Nesting: Mostly shallow, although the undirected traversal has nested loops and a conditional that require some tracking. Clarity of intent: Descriptive names and comments explain duplicate avoidance, self-loops, and null safety; however, the opaque, unused boolean block in the Directed constructor introduces unexplained noise. Code length: Implementation is reasonably concise; the lengthy traversal example is useful documentation, while the boolean block is unnecessary. Action granularity: Most lines perform one clear action, but the inserted block compresses declaration, bitwise arithmetic, and reassignment into one line. Reading flow: Factory, shared advancement, and specialized traversal form a natural progression. The malformed-looking indentation of the inserted block interrupts that flow, and nullable state plus infinite-loop traversal demand extra attention.
Run 3
Code Structure: Shared iterator state and separate directed/undirected implementations provide logical organization. Nesting: Mostly shallow, although the undirected traversal uses nested loops and a conditional. Clarity of intent: Descriptive names and detailed comments explain traversal, duplicate suppression, null handling, and self-loops; the meaningless obfuscated boolean block in the Directed constructor sharply detracts from clarity. Code length: Implementation is reasonably concise, but the extensive example and redundant boolean statements add bulk. Action granularity: Most lines perform one action; the injected constructor block compresses multiple statements onto one line. Reading flow: Factory, initialization, advancement, and specialized implementations follow a natural sequence, disrupted by the poorly formatted constructor block and mildly intricate nullable state management.