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Understanding the Java `final` Keyword and Immutability

Final is not equal to object immutable in Java. It only ensures that variable references cannot be reassigned, but does not guarantee that the state of the object pointed to is immutable; 2. For basic types, final ensures that the value remains unchanged; for object types, references are immutable but the object content can still be modified; 3. Really immutable must be met: the class is declared final, all fields are privatefinal, no setter method, constructor initialization and no mutable state is leaked; 4. If the field is a mutable object, external modifications need to be prevented by defensive copying and returning an unmodified view; 5. Final field has the JMM memory model guarantee to ensure that the objects are correctly published under multiple threads; 6. Common misunderstanding is that final automatically brings inability to be unhealthy; 6. The common misunderstanding is that final automatically brings inability; 5. Final field has the guarantee of JMM memory model to ensure that the object is published correctly; 6. Common misunderstanding is that final automatically brings inability;

Jul 27, 2025 am 01:33 AM

Creating a REST Client in Java using `HttpClient`

The built-in HttpClient in Java11 and above provides a simple REST client implementation. 1. Use HttpClient.newBuilder() to configure timeouts, proxying, etc. and create reusable client instances; 2. Set URI, GET/POST/PUT/DELETE methods, request headers and BodyPublisher through HttpRequest.newBuilder() to send synchronous or asynchronous requests; 3. Use HttpResponse.BodyHandlers to process response bodies, supporting strings, files or byte arrays; 4. Asynchronous requests are combined with thenApply through sendAsync() combined with thenApply

Jul 27, 2025 am 01:28 AM

Advanced Error Handling in Java Microservices

Use@ControllerAdviceforglobalexceptionhandlingtocentralizeerrorresponsesandreduceduplication.2.DefineastructuredErrorResponseDTOwithcode,message,timestamp,andpathforconsistentclientcommunication.3.ImplementcircuitbreakersusingResilience4jtopreventcas

Jul 27, 2025 am 01:14 AM

Advanced Java Multithreading: from synchronized to Lock-Free Algorithms

synchronized is the earliest synchronization mechanism in Java. It is simple and easy to use and has good performance after optimization, but lacks flexibility; 2. ReentrantLock provides advanced functions such as interruptibility, reentrant, and support fairness, which is suitable for scenarios that require fine control; 3. The lock-free algorithm implements non-blocking concurrency based on CAS, such as AtomicLong, LongAdder and ConcurrentLinkedQueue, which performs better in a high-competitive environment, but needs to deal with ABA problems and CPU spin overhead; ultimately, appropriate strategies should be selected based on concurrency strength: synchronized for low-competitive competition, ReentrantLock needs to be used for control, and lock-free structure for high-concurrency scenarios, from

Jul 27, 2025 am 01:13 AM

How to Use the Java `sealed` Classes and Interfaces

When using sealed classes or interfaces, the allowed subclasses must be explicitly listed through permits; 2. Each allowed subclass must be marked as final, sealed or non-sealed; 3. All subclasses must be in the same module or package as the parent class and are directly inherited; 4. It cannot be used with anonymous or local classes; 5. Combining records and pattern matching can achieve type safety and exhaustive checks. Java's sealed classes and interfaces make the type hierarchy safer and predictable by restricting inheritance relationships, and are suitable for modeling closed class variants, such as expression types or state machines. The compiler can ensure that switch expressions handle all situations, thereby improving the maintainability and correctness of the code.

Jul 27, 2025 am 12:55 AM

java

Hexagonal Architecture for Maintainable Java Enterprise Applications

Hexagonal Architecture is a software architecture model that improves system maintainability, testability and scalability by decoupling core business logic from external dependencies. 1. The core area includes business logic and use cases, which are implemented independently of the framework and technology; 2. Port defines interactive interfaces, divided into primary port (inbound) and secondary port (outbound); 3. Adapter implements ports, responsible for communicating with external systems, such as web controllers or database access components; 4. In Java, dependencies are isolated through interfaces, and the business layer does not introduce framework annotations, and only uses adapters through dependency injection; 5. In practice, excessive layering and direct calls between adapters should be avoided, and the core logic can be verified by unit tests. This architecture

Jul 27, 2025 am 12:44 AM

java Architecture

Java 17 LTS vs. Java 21: Key Features and Migration Guide

Compared with Java17, Java21 has significantly improved concurrency, language features and performance. It is recommended to migrate as soon as possible. 1. Virtual threads (formal) greatly reduce resource overhead in high concurrency scenarios and simplify asynchronous programming; 2. Structured concurrency (preview) improves the readability and reliability of multi-threaded code; 3. Pattern matching and recording patterns enhance conditional judgment and data deconstruction capabilities; 4. ZGC supports concurrent class unloading to reduce pause time; 5. Default UTF-8 encoding solves cross-platform garbled code problems; 6. External functions and memory APIs provide safer local calling methods; dependency compatibility (such as SpringBoot3), adjust JVM parameters, update build configuration, enable preview features and conduct full testing, especially

Jul 27, 2025 am 12:42 AM

java lts

The Complete Guide to the Java `Optional` Class

Optional is a container class introduced by Java 8 for more secure handling of potentially null values, with the core purpose of which is to explicitly "missing value" and reduce the risk of NullPointerException. 1. Create an empty instance using Optional.empty(), Optional.of(value) wraps non-null values, and Optional.ofNullable(value) safely wraps the value of null. 2. Avoid combining isPresent() and get() directly. You should give priority to using orElse() to provide default values. OrElseGet() implements delay calculation. This method is recommended when the default value is overhead.

Jul 27, 2025 am 12:22 AM

java optional

Debugging and Troubleshooting Common Java Application Issues

Checkstacktracesforexceptions,identifyingrootcauseslikenullpointersorclasspathissues.2.UseprofilingtoolslikeVisualVMandanalyzeheapdumpstodiagnosememoryleaksandhighCPUusage.3.InspectdependencytreeswithMavenorGradletoresolvemissingorconflictingJARsandv

Jul 26, 2025 am 08:04 AM

Implementing OAuth2 and OpenID Connect in a Java Application

OAuth2 is used for authorization, OpenIDConnect (OIDC) provides identity authentication based on OAuth2 to confirm user identity. 2. Using SpringBoot and SpringSecurity is the recommended way to implement OIDC in Java, and spring-boot-starter-oauth2-client dependency needs to be introduced. 3. Configure client-id, client-secret, scope (including openid, profile, email) and issuer-uri in application.yml to enable automatic metadata discovery. 4.

Jul 26, 2025 am 08:03 AM

Implementing the Saga Pattern in a Java Distributed System

Use the Saga mode to maintain data consistency in Java distributed systems, and replace distributed transactions through local transaction sequences and compensation mechanisms; 2. It is recommended to use orchestrated Saga in SpringBoot, and the OrderSaga class coordinates the execution and rollback of payment and inventory services; 3. Add retry, idempotence, and persistent Saga states to enhance reliability; 4. Linear process optimization orchestration is considered in complex event-driven scenarios.

Jul 26, 2025 am 07:56 AM

Comparing Java Web Servers: Tomcat vs Jetty vs Undertow

UseTomcatforenterpriseenvironmentsneedingbroadcompatibilityandtoolingsupport.2.ChooseJettyformodular,embeddableapplicationswithheavyasyncorWebSocketusage.3.OptforUndertowwhenhighperformance,lowlatency,andnon-blockingI/Oarecritical,especiallyinmodernm

Jul 26, 2025 am 07:51 AM

Java Reflection API: Power and Pitfalls

The core answer to reflection is: it is a double-edged sword that can realize dynamic operational structures at runtime, but it needs to be used with caution to avoid performance, safety and maintenance issues. 1. The power of reflection lies in dynamically creating objects, calling methods, accessing private members and extracting generic type information, which is widely used in frameworks such as Spring and Hibernate. 2. The main risks include high performance overhead, disruption of packaging, runtime errors caused by bypassing compile-time checks, and compatibility issues with new features such as Java module systems. 3. Suitable for use in framework development, plug-in systems, unit testing and generic type recovery, and should be avoided in ordinary business logic, performance-sensitive scenarios, or polymorphic substitutions. 4. Best practices include priority use of interface design and ease of

Jul 26, 2025 am 07:50 AM

Understanding Bytecode and the Java Compilation Process

Java programs do not run directly on the computer, but are first compiled into bytecode and then executed by the JVM; 1.javac compiles the .java file into platform-independent bytecode (.class file); 2. JVM's class loader loads the .class file; 3. Bytecode validator checks security; 4. JVM executes bytecode through the interpreter, and the JIT compiler dynamically compiles the hotspot code into local machine code to improve performance; this mechanism realizes Java's "write once, run everywhere", while ensuring security and execution efficiency. Finally, through tools such as Java, you can also view bytecode instructions, which fully demonstrates the entire process from Java source code to local execution.

Jul 26, 2025 am 07:49 AM

java Compilation principle