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How to create a sealed class in Java

Java17 and above support sealed classes, and the allowed subclasses are defined through the sealed keyword and permits clause, and each direct subclass must be declared as final, sealed or non-sealed. 1. Use sealed to modify the class, 2. List allowed subclasses through permits, 3. Ensure that each subclass clearly marks its sealed state, and all relevant classes must be in the same module or package. This mechanism provides compile-time inheritance control, improving pattern matching security and domain modeling accuracy. Summary: Java17 can achieve controlled inheritance through the sealed permits subclass modifier.

Aug 20, 2025 pm 01:32 PM

java 密封類

Debugging 'Teen Talk' program: Solve infinite loop problem

This article aims to help readers debug a Java program called "Teen Talk" that is designed to simulate how teenagers talk, adding "like" after each space. The article analyzes the causes of infinite loops in the program and provides modified code examples to ensure that the program runs correctly and outputs the expected results.

Aug 20, 2025 pm 01:12 PM

Java multithreaded task scheduling: Efficiently handle shared list tasks with ExecutorService

This article explores in-depth how to efficiently and safely assign and execute tasks from shared tasks lists in a Java multithreaded environment. In view of the complexity of manually managing task distribution, the article focuses on recommending and elaborating on ExecutorService as a core solution. It automates task scheduling through internal mechanisms to ensure that thread resources are fully utilized. The article provides detailed Java code examples and discusses BlockingQueue as the underlying implementation principle, while highlighting key considerations when using concurrency tools, aiming to help developers build robust concurrent applications.

Aug 20, 2025 pm 01:06 PM

What is the lifecycle of a thread in Java?

The life cycle of a Java thread includes six states: New, Runnable, Blocked, Waiting, TimedWaiting and Terminated; when creating a thread through Thread or Runnable, it is in the New state, and after calling start(), it becomes Runnable, waiting for CPU scheduling to execute. If you try to obtain a synchronization lock, it enters the Blocked state. Calling wait() or join() and other methods will enter the Waiting or TimedWaiting state, waiting for a specific event or timeout to resume, the run() method will be executed or terminated abnormally and cannot

Aug 20, 2025 pm 01:05 PM

java thread

What is the purpose of the static keyword in Java?

ThestatickeywordinJavaisusedtocreateclass-levelmembersthatbelongtotheclassratherthananyinstance,allowingthemtobeaccessedwithoutcreatinganobject;staticvariablesaresharedamongallinstancesandinitializedwhentheclassisloaded,staticmethodscanonlyaccessstat

Aug 20, 2025 pm 12:58 PM

Practice of service layer return type conversion and data model mapping in Java

This article discusses the type conversion problem caused by mismatch between the service layer and the controller layer in Java applications. In the scenario where the service layer returns an Object type and needs to be converted to a specific business object (such as Resresource) at the controller layer, the article details how to implement smooth conversion between different data structures (such as Excel and Resresource) through a custom data mapper (Mapper), thereby ensuring type safety and code maintainability.

Aug 20, 2025 pm 12:57 PM

Doctors in Spring Boot-Patient Relationship and Permission Management Practice

This article discusses effective strategies for managing doctor-patient relationships and their authority control in Spring Boot applications. For multi-role users and complex business relationships, the article compares multiple data models in detail and recommends a hybrid solution that combines common user authentication and specific role data separation. Through clear physical design, JPA annotation application and security considerations, we aim to provide a solution that is clear, easy to scale and meets actual business needs.

Aug 20, 2025 pm 12:54 PM

Loading GLSL Shader in Vulkan using Java

This document describes how to load and use GLSL shaders using the Vulkan API in Java. Compile GLSL shader into SPIR-V binary files through ShaderSPIRVUtils tool, and provides a GitHub tutorial link to help developers get started quickly and realize shader integration in the Vulkan pipeline.

Aug 20, 2025 pm 12:48 PM

Architecting a Multi-Tenant SaaS Application in Java

Chooseamulti-tenantstrategysuchassharedschema,schema-per-tenant,ordedicateddatabasebasedonisolation,cost,andscalabilityneeds;2.Identifytenantsearlyusinghostheader,JWT,orcustomheadersviaafilterinSpringBootandstoretenantcontextinThreadLocal;3.Implement

Aug 20, 2025 pm 12:46 PM

Mapping strategy in Spring JDBC that handles inconsistent Bean attributes and database column names

This article aims to solve the problem that Spring JDBC BeanPropertyRowMapper cannot automatically map when Java Bean property names are inconsistent with database column names. When non-JPA entity classes encounter such a situation, the annotation such as @Column cannot take effect. The core solution is to implement a custom RowMapper interface that accurately maps data by manually specifying column names, ensuring that the data can be correctly populated from the ResultSet into a Java Bean object.

Aug 20, 2025 pm 12:45 PM

Automate the mount and formatting of EBS volumes for AWS Windows EC2 instances

This article details how to use the cfn-init function of AWS CloudFormation, combined with PowerShell scripts to achieve automated mount and formatting of newly added EBS volumes on AWS Windows EC2 instances. The content covers rapid configuration methods for single block EBS volumes, as well as dynamic identification strategies for handling multiple blocks or uncertain drive letter EBS volumes, and provides best practices and considerations for integrating into CloudFormation templates, aiming to help users efficiently and reliably manage storage expansion of EC2 instances.

Aug 20, 2025 pm 12:42 PM

Log4j2 JsonTemplateLayout Stack Trace Pollution Problems and Solutions

When using Log4j2's JsonTemplateLayout, if configured improperly, the stack trace of the exception may unexpectedly be attached to other JSON fields, especially those using the pattern parser. This is because JsonTemplateLayout delegates to PatternLayout when processing the pattern parser, and PatternLayout enables stackTraceEnabled by default. The solution to this problem is to explicitly set stackTraceEnabled: false in each affected pattern parser configuration

Aug 20, 2025 pm 12:39 PM

How to use System.out.println in Java

System.out.println is the core method used in Java to output and break lines to the console. 1. It consists of System class, out static members and println() method; 2. It can print strings, variables, expressions, numbers and objects, etc.; 3. It does not need to import the java.lang package when using it; 4. Println() automatically wraps lines, if you do not need to break lines, print() should be used; 5. It is automatically called toString() method when printing objects. It is recommended to rewrite this method to obtain meaningful output; 6. Be careful to avoid missing brackets, semicolons or using uninitialized variables, and printing null values will output "null" without an error; this side

Aug 20, 2025 pm 12:37 PM

Android in-app HTTP server: AlertDialog interaction and response processing

This document describes how to deploy an HTTP server within an Android application and interact with the user via AlertDialog when requests are received. By listening to the button click event of AlertDialog, the server can send a response to the client according to the user's choice. At the same time, a simple blocking method is provided to ensure that the user interaction is completed before sending a response, and the potential performance impact is discussed.

Aug 20, 2025 pm 12:36 PM