About Me
Oracle Certified Professional Java SE 11 Developer
1 Java Fundamentals
1-1 Java Basics
1-1 1 Java Platform Overview
1-1 2 Java Development Environment
1-1 3 Java Program Structure
1-1 4 Java Virtual Machine (JVM)
1-1 5 Java Development Kit (JDK)
1-1 6 Java Runtime Environment (JRE)
1-2 Object-Oriented Programming (OOP) Concepts
1-2 1 Classes and Objects
1-2 2 Inheritance
1-2 3 Polymorphism
1-2 4 Encapsulation
1-2 5 Abstraction
1-2 6 Interfaces
1-2 7 Abstract Classes
1-3 Data Types and Variables
1-3 1 Primitive Data Types
1-3 2 Reference Data Types
1-3 3 Variable Declaration and Initialization
1-3 4 Type Conversion and Casting
1-3 5 Arrays
1-4 Control Flow
1-4 1 Conditional Statements (if, else, switch)
1-4 2 Looping Constructs (for, while, do-while)
1-4 3 Break and Continue Statements
1-4 4 Exception Handling
2 Java Collections Framework
2-1 Collections Overview
2-1 1 Collection Interfaces
2-1 2 Collection Classes
2-1 3 Collection Algorithms
2-2 Lists
2-2 1 ArrayList
2-2 2 LinkedList
2-2 3 List Operations
2-3 Sets
2-3 1 HashSet
2-3 2 TreeSet
2-3 3 LinkedHashSet
2-4 Maps
2-4 1 HashMap
2-4 2 TreeMap
2-4 3 LinkedHashMap
2-5 Queues and Deques
2-5 1 PriorityQueue
2-5 2 ArrayDeque
3 Java Streams and Lambda Expressions
3-1 Lambda Expressions
3-1 1 Lambda Syntax
3-1 2 Functional Interfaces
3-1 3 Method References
3-2 Streams
3-2 1 Stream Creation
3-2 2 Intermediate Operations
3-2 3 Terminal Operations
3-2 4 Parallel Streams
4 Java Concurrency
4-1 Threads
4-1 1 Thread Creation
4-1 2 Thread States
4-1 3 Thread Synchronization
4-1 4 Thread Communication
4-2 Concurrency Utilities
4-2 1 Executor Framework
4-2 2 Concurrent Collections
4-2 3 Atomic Variables
4-2 4 Locks
5 Java IO and NIO
5-1 Input and Output Streams
5-1 1 Byte Streams
5-1 2 Character Streams
5-1 3 Buffered Streams
5-2 File IO
5-2 1 File Class
5-2 2 FileReader and FileWriter
5-2 3 FileInputStream and FileOutputStream
5-3 NIO (New IO)
5-3 1 Path Interface
5-3 2 Files Class
5-3 3 Channels and Buffers
5-3 4 Asynchronous IO
6 Java Date and Time API
6-1 Date and Time Classes
6-1 1 LocalDate
6-1 2 LocalTime
6-1 3 LocalDateTime
6-1 4 ZonedDateTime
6-2 Period and Duration
6-2 1 Period Class
6-2 2 Duration Class
6-3 Time Zones and Calendars
6-3 1 TimeZone Class
6-3 2 Calendar Class
7 Java Modules
7-1 Module System Overview
7-1 1 Module Declaration
7-1 2 Module Path
7-1 3 Module Dependencies
7-2 Module Resolution
7-2 1 Automatic Modules
7-2 2 Named Modules
7-2 3 Unnamed Modules
7-3 Module Services
7-3 1 Service Provider Interface (SPI)
7-3 2 ServiceLoader Class
8 Java Security
8-1 Security Basics
8-1 1 Security Manager
8-1 2 Permissions
8-1 3 Policy Files
8-2 Cryptography
8-2 1 Key Generation
8-2 2 Encryption and Decryption
8-2 3 Digital Signatures
8-3 Secure Coding Practices
8-3 1 Input Validation
8-3 2 Secure Communication
8-3 3 Authentication and Authorization
9 Java Networking
9-1 Networking Basics
9-1 1 InetAddress Class
9-1 2 URL and URLConnection Classes
9-2 Sockets
9-2 1 Socket Class
9-2 2 ServerSocket Class
9-2 3 DatagramSocket Class
9-3 Networking Protocols
9-3 1 TCPIP
9-3 2 UDP
9-3 3 HTTP
10 Java Database Connectivity (JDBC)
10-1 JDBC Basics
10-1 1 JDBC Architecture
10-1 2 JDBC Drivers
10-1 3 Establishing a Connection
10-2 Executing SQL Statements
10-2 1 Statement Interface
10-2 2 PreparedStatement Interface
10-2 3 CallableStatement Interface
10-3 ResultSet
10-3 1 ResultSet Interface
10-3 2 ResultSetMetaData Interface
10-4 Transaction Management
10-4 1 Commit and Rollback
10-4 2 Savepoints
11 Java Annotations
11-1 Annotation Basics
11-1 1 Annotation Types
11-1 2 Meta-Annotations
11-1 3 Annotation Processing
11-2 Standard Annotations
11-2 1 @Override
11-2 2 @Deprecated
11-2 3 @SuppressWarnings
11-3 Custom Annotations
11-3 1 Annotation Creation
11-3 2 Annotation Usage
12 Java Reflection
12-1 Reflection Basics
12-1 1 Class Class
12-1 2 Field Class
12-1 3 Method Class
12-2 Dynamic Class Loading
12-2 1 ClassLoader Class
12-2 2 Dynamic Proxy
12-3 Reflection API
12-3 1 Accessing Class Members
12-3 2 Modifying Class Members
13 Java Internationalization (I18N)
13-1 I18N Basics
13-1 1 Locale Class
13-1 2 ResourceBundle Class
13-2 Formatting
13-2 1 NumberFormat Class
13-2 2 DateFormat Class
13-2 3 MessageFormat Class
13-3 Character Encoding
13-3 1 Charset Class
13-3 2 String Encoding and Decoding
14 Java Platform Module System (JPMS)
14-1 Module System Overview
14-1 1 Module Declaration
14-1 2 Module Path
14-1 3 Module Dependencies
14-2 Module Resolution
14-2 1 Automatic Modules
14-2 2 Named Modules
14-2 3 Unnamed Modules
14-3 Module Services
14-3 1 Service Provider Interface (SPI)
14-3 2 ServiceLoader Class
15 Java 11 New Features
15-1 New String Methods
15-1 1 isBlank()
15-1 2 lines()
15-1 3 repeat()
15-2 New File Methods
15-2 1 writeString()
15-2 2 readString()
15-3 Local-Variable Syntax for Lambda Parameters
15-3 1 var Keyword in Lambda Expressions
15-4 HTTP Client API
15-4 1 HttpClient Class
15-4 2 HttpRequest Class
15-4 3 HttpResponse Class
15-5 Nest-Based Access Control
15-5 1 Nest Host and Nest Members
15-5 2 Nest Access Control
15-6 Epsilon Garbage Collector
15-6 1 Epsilon GC Overview
15-6 2 Epsilon GC Use Cases
15-7 Flight Recorder
15-7 1 Flight Recorder Overview
15-7 2 Flight Recorder Use Cases
15-8 Application Class-Data Sharing (CDS)
15-8 1 CDS Overview
15-8 2 CDS Use Cases
15-9 Deprecations and Removals
15-9 1 Deprecated Features
15-9 2 Removed Features
7.2.3 Unnamed Modules Explained

7.2.3 Unnamed Modules Explained

Unnamed modules in Java SE 11 are a mechanism to handle legacy code that has not been modularized. They provide a way to integrate non-modular code into the modular system, ensuring compatibility and smooth migration. Understanding unnamed modules is crucial for managing and modernizing existing Java applications.

Key Concepts

1. Unnamed Module Definition

An unnamed module is a special kind of module that includes all classes loaded from the classpath. It does not have a module-info.java file and does not explicitly declare any dependencies or exports. Unnamed modules can access all other modules, including named and automatic modules.

Example

        java -classpath lib/legacy.jar com.example.legacy.Main

2. Classpath Integration

Unnamed modules are created automatically when classes are loaded from the classpath. This allows legacy code to coexist with modular code without requiring immediate refactoring. The classpath is still supported for backward compatibility, but it is recommended to migrate to the module path for better modularity.

Example

        java -classpath lib/legacy.jar:lib/another.jar com.example.legacy.Main

3. Access to Named Modules

Unnamed modules have full access to all named modules. This means that classes in unnamed modules can use classes from named modules without any restrictions. However, the reverse is not true; named modules cannot access classes in unnamed modules unless specific provisions are made.

Example

        java -classpath lib/legacy.jar --module-path mods -m myapp/com.example.Main

4. Migration Strategy

Unnamed modules provide a transitional strategy for migrating legacy code to the modular system. Developers can gradually modularize their code by moving classes from the classpath to the module path and adding module-info.java files. This phased approach minimizes disruption and allows for a smoother transition.

Example

        java -classpath lib/legacy.jar --module-path mods:lib/modular.jar -m myapp/com.example.Main

Examples and Analogies

Think of unnamed modules as a bridge between the old and new worlds of Java development. Just as a bridge allows people to cross from one side to the other, unnamed modules allow legacy code to interact with modular code. For example, if you have an old library that is not modular, you can still use it in a new modular application by placing it on the classpath, and it will be treated as part of an unnamed module.

By understanding unnamed modules, you can effectively manage and modernize your Java applications, ensuring that they are well-organized, maintainable, and ready for future enhancements.

© 2024 Ahmed Baheeg Khorshid. All rights reserved.