Add collections module: HashMap bucket layout, treeification, and a real ConcurrentModificationException reproduction

Companion code for the ankurm.com post "Top 40 Java Collections Interview Questions (HashMap Internals to Fail-Fast Iterators)". Verified against JDK 25's own HashMap source (TREEIFY_THRESHOLD=8, UNTREEIFY_THRESHOLD=6, MIN_TREEIFY_CAPACITY=64), with every claim backed by a committed docs/output/*.txt transcript from a real run. Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01YXCrLgRKFgCh9RHKW8xaqJ
2026-10-01 04:27:27 +00:00
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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>com.ankurm.interviewlab</groupId>
+  <artifactId>collections</artifactId>
+  <version>1.0.0</version>
+  <packaging>jar</packaging>
+
+  <name>java-interview-lab :: collections</name>
+  <description>
+    Runnable companion code for ankurm.com's "Top 40 Java Collections Interview Questions"
+    article: HashMap bucket-layout dumps via reflection, a real treeification trigger, a real
+    ConcurrentModificationException reproduction (and a real case where fail-fast silently does
+    NOT fire), and equals/hashCode contract-violation demos.
+  </description>
+
+  <properties>
+    <maven.compiler.release>25</maven.compiler.release>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <junit.version>5.11.0</junit.version>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter</artifactId>
+      <version>${junit.version}</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <finalName>collections</finalName>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>3.13.0</version>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <version>3.3.1</version>
+        <configuration>
+          <!-- Transcript tests reflect into java.util.HashMap's internal table field;
+               the JPMS module system refuses setAccessible(true) on a JDK-internal
+               field across module boundaries without this. Forgetting it is the
+               single most common failure mode for this module (see README). -->
+          <argLine>--add-opens java.base/java.util=ALL-UNNAMED</argLine>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>