Build Systems — Maven & Gradle

8. Practice Problems

Most answers are text or configuration — some are runnable Java demos of the underlying concept.

1. Write a Java program that prints the three parts of a Maven coordinate given a combined string like "com.google.guava:guava:33.0.0-jre".
   "com.google.guava:guava:33.0.0-jre"-এর মতো string থেকে groupId, artifactId, version আলাদা করে প্রিন্ট করুন।
   ✨ Show Answer

   Main.java

   class Main {
       public static void main(String[] args) {
           String coord = "com.google.guava:guava:33.0.0-jre";
           String[] parts = coord.split(":");
           System.out.println("groupId    = " + parts[0]);
           System.out.println("artifactId = " + parts[1]);
           System.out.println("version    = " + parts[2]);
       }
   }

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2. What does mvn install do that mvn package doesn't?
   mvn install যা করে কিন্তু mvn package করে না — সেটি কী?
   ✨ Show Answer

   Answer: mvn package builds the JAR/WAR in target/. mvn install does everything package does AND then copies the artifact into your local Maven cache at ~/.m2/repository, so that other local projects on your machine can resolve it by coordinate.

   mvn package শুধু target/-এ JAR/WAR তৈরি করে; mvn install সেটিকে আরো local Maven cache (~/.m2/repository)-এ copy করে — যাতে একই মেশিনের অন্য project সেটিকে dependency হিসেবে পায়।

3. Write a Java program that simulates a tiny "build" — it prints the phases compile → test → package → install in order, skipping any phase named as a command-line argument.
   একটি ছোট "build" simulator বানান — compile → test → package → install প্রিন্ট করবে, কিন্তু command-line-এ যে phase দেওয়া হবে সেটি skip করবে।
   ✨ Show Answer

   Main.java

   class Main {
       public static void main(String[] args) {
           String[] phases = {"compile", "test", "package", "install"};
           String skip = args.length > 0 ? args[0] : "";
           for (String p : phases) {
               if (p.equals(skip)) { System.out.println("[SKIP] " + p); continue; }
               System.out.println("[RUN ] " + p);
           }
       }
   }

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4. Which scope would you use for (a) JUnit, (b) a PostgreSQL JDBC driver, (c) the Servlet API (Tomcat provides it)?
   কোন scope লাগবে — (ক) JUnit, (খ) PostgreSQL JDBC driver, (গ) Servlet API (Tomcat দেবে)?
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   Answer: (a) test / testImplementation — JUnit only exists during tests. (b) runtime / runtimeOnly — you never import a driver class in your code; it is loaded reflectively at runtime. (c) provided / compileOnly — you need it to compile your servlet but the container provides it, so shipping it in your WAR would conflict.

5. Explain "transitive dependency" and why version conflicts are possible.
   "Transitive dependency" কী, এবং কেন version conflict হতে পারে — ব্যাখ্যা করুন।
   ✨ Show Answer

   Answer: If your project depends on A, and A depends on B, then B is a transitive dependency — you did not name it, but it arrives on your classpath anyway. Version conflicts happen when two direct dependencies pull in different versions of the same transitive dep (Maven picks "nearest" in the dependency tree; Gradle picks "highest" by default). Resolve with the dependencyManagement section in Maven or a Gradle resolutionStrategy to force a version.