Java Modules (JPMS) & Modern Packaging

8. Practice Problems

1. Write a module-info.java for a hypothetical com.abcltech.utils module that depends on java.logging and exports a package com.abcltech.utils.text.
   একটি module-info.java লিখুন — com.abcltech.utils module, java.logging-এর উপর নির্ভরশীল, com.abcltech.utils.text export করে।
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   module-info.java

   module com.abcltech.utils {
       requires java.logging;
       exports com.abcltech.utils.text;
   }

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2. Write a Java program that prints java.base, java.sql, and your own class's module names.
   একটি Java program লিখুন যা java.base, java.sql ও আপনার নিজের class-এর module print করবে।
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   Main.java

   class Main {
       public static void main(String[] args) throws Exception {
           System.out.println("String     -> " + String.class.getModule());
           System.out.println("Connection -> " + Class.forName("java.sql.Connection").getModule());
           System.out.println("Main       -> " + Main.class.getModule());
       }
   }

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3. Explain the difference between exports and opens.
   exports এবং opens-এর পার্থক্য ব্যাখ্যা করুন।
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   Answer: exports makes the package visible at compile time AND for normal runtime access — other modules can import and call its public types. opens additionally permits deep reflection (including private members) at runtime, but does not permit compile-time imports. Frameworks like Hibernate and Jackson need opens to read your private fields via reflection; ordinary consumers only need exports.

4. You're shipping a small JavaFX desktop app to Bangladeshi users who do not have Java installed. Which tool creates the .msi installer?
   একটি JavaFX desktop app ব্যবহারকারীদের কাছে পাঠাতে চান — তাদের কাছে Java নেই। কোন টুল দিয়ে .msi installer বানাবেন?
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   Answer: jpackage. It bundles your application, the JavaFX modules, and a slimmed-down JDK produced by jlink into a single native installer. The end user just double-clicks the .msi — no separate JDK, no setup steps.

5. Write a runnable program that lists every "java.*" module currently loaded in the boot layer and counts them.
   একটি program লিখুন যা boot layer-এ লোড হওয়া সব java.* module তালিকা করবে এবং সংখ্যা গুণে দেখাবে।
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   Main.java

   class Main {
       public static void main(String[] args) {
           long n = ModuleLayer.boot().modules().stream()
               .map(Module::getName)
               .filter(name -> name.startsWith("java."))
               .peek(System.out::println)
               .count();
           System.out.println("\nTotal java.* modules: " + n);
       }
   }

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