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
15.8.1 CDS Overview Explained

15.8.1 CDS Overview Explained

Class Data Sharing (CDS) is a feature introduced in Java SE 11 that aims to improve the startup time and reduce the memory footprint of Java applications. CDS allows multiple JVMs to share a common set of classes in memory, which can significantly enhance performance and resource utilization.

Key Concepts

1. Class Data Sharing (CDS)

CDS is a mechanism that enables the sharing of class metadata between multiple JVM instances. By storing the metadata of frequently used classes in a shared archive, CDS reduces the time and resources required to load these classes, leading to faster application startup and lower memory usage.

Example

        java -Xshare:dump
        java -Xshare:on -jar MyApplication.jar

2. Shared Archive

A shared archive is a file that contains the metadata of classes that can be shared between JVMs. The JVM creates this archive during the first run and uses it in subsequent runs to load classes more efficiently.

Example

        java -Xshare:dump
        java -Xshare:on -jar MyApplication.jar

3. Startup Time Improvement

By using CDS, the JVM can load classes from the shared archive instead of parsing and loading them individually. This reduces the time required to start the application, making it more responsive.

Example

        Before CDS: Application startup time = 5 seconds
        After CDS: Application startup time = 2 seconds

4. Memory Footprint Reduction

Since the shared archive contains pre-loaded class metadata, multiple JVMs can share this data, reducing the overall memory footprint. This is particularly beneficial in environments with multiple JVM instances running concurrently.

Example

        Before CDS: Memory usage per JVM = 500 MB
        After CDS: Memory usage per JVM = 400 MB

Examples and Analogies

Think of CDS as a library of frequently used books. Instead of each student (JVM instance) bringing their own copy of the books, they share a common library (shared archive). This reduces the time it takes to get the books (load classes) and the space required to store them (memory footprint).

For instance, if you are running multiple instances of a web application, using CDS can help reduce the startup time and memory usage of each instance. This makes the application more efficient and responsive, especially in high-concurrency environments.

Example

        java -Xshare:dump
        java -Xshare:on -jar WebApplication.jar

By mastering the concepts of Class Data Sharing, you can optimize the performance and resource utilization of your Java applications, making them more efficient and scalable.

© 2024 Ahmed Baheeg Khorshid. All rights reserved.