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Technical Articles

Java

javaTutorial

What are design patterns in Java?

DesignpatternsinJavaareprovensolutionstorecurringsoftwaredesignproblems,categorizedintocreational,structural,andbehavioraltypes;theypromoteflexibilityandmaintainabilitythroughtemplates—notdirectcode—usingobject-orientedprincipleslikeinheritanceandpol

Aug 25, 2025 am 11:10 AM

java Design Patterns

Use Java Stream to find elements with maximum values ??in List

This article describes how to use the Java Stream API to find a HashMap with the largest "Length" value from an ArrayList. The article first suggests using a custom object instead of a HashMap to store data, and then shows two ways to find a single largest element and find all sets of elements with maximum values, and provides detailed code examples. Additionally, an alternative to using the three-parameter Stream.collect() method is provided to avoid creating intermediate maps.

Aug 25, 2025 am 10:48 AM

How to work with the Java Memory Model

To effectively use the Java memory model, you must first understand that it ensures the visibility and order of variables through the happens-before relationship; 1. Use volatile to ensure that variable read and write directly interacts with the main memory, ensuring visibility but not the atomicity of composite operations; 2. Create happens-before relationship through synchronized blocks or methods to ensure that the write before lock is released is visible to the threads that acquire the same lock in the subsequent memory; 3. Use Thread.start() and Thread.join() to achieve memory visibility between threads; 4. Use atomic classes, concurrent collections and lock tools in the java.util.concurrent package, which are built-in

Aug 25, 2025 am 10:40 AM

Efficient way to find maximum values ??in List using Java Stream

This article explores how to use the Java Stream API to find a HashMap with the maximum length from a List. The article first emphasizes the advantages of using custom objects instead of HashMap, and then introduces two methods to find a single largest element and find all sets of elements with maximum length, and provides clear code examples and detailed explanations to help readers better understand and apply the Stream API.

Aug 25, 2025 am 10:33 AM

What is the Stream API and its benefits in Java?

Java8's StreamAPI provides powerful and declarative data processing methods. 1. Supports functional programming through method chains to make the code more concise and easy to read; 2. Provides rich intermediate operations (such as filter, map, sorted) and terminal operations (such as forEach, collect, reduce), which facilitates the construction of complex data processing pipelines; 3. Parallel processing can be achieved through parallelStream() or stream().parallel(), automatically manages multi-threaded task division and result merging, and improves the processing performance of large data sets; 4. Improves code maintainability, reduces the use of loops and temporary variables, and clearly expresses the operation intention; 5.

Aug 25, 2025 am 10:26 AM

How to get a substring in Java

To get substrings in Java, you need to use the substring() method of the String class. This method has two overloaded forms: 1.substring(intbeginIndex) returns the substring from the specified index to the end of the string; 2.substring(intbeginIndex,intendIndex) returns the characters from beginIndex to endIndex (not included). The index starts at 0 and endIndex is an exclusive value. If the index goes out of bounds, an IndexOutOfBoundsException will be thrown. When using it, make sure the index is valid or bounds are checked in advance to avoid exceptions.

Aug 25, 2025 am 10:24 AM

Understanding standard output buffering: behavioral differences and control methods for Python, C, Java, and Go

This article explores in-depth differences in standard output (stdout) buffering mechanisms for different programming languages ??(Python, C, Java, Go), especially the different behaviors that appear when the output is connected to a terminal (TTY) or a pipeline. We will parse why Python and C adopt block buffering by default in non-TTY environments, while Java and Go tend to always use line buffering, and provide practical methods to control output immediacy, such as the flush=True parameter in Python.

Aug 25, 2025 am 10:18 AM

A variant that implements the Optional.or() method

This article aims to guide developers how to implement variants of the or() method of the Optional class. This method receives a Supplier that provides an Optional and returns the Optional provided by the Supplier when the original Optional is empty. The article will dig into the issues encountered when accessing private fields and provide a variety of solutions, including using intermediate variables and type conversions, and analyzing their respective pros and cons.

Aug 25, 2025 am 10:06 AM

Advanced Java Generics and Wildcards Explained

WildcardsinJavagenericsincludeunbounded(?),upper-bounded(?extendsT),andlower-bounded(?superT),withthePECSprincipleguidingtheiruse:use?extendsTforproducers(reading)and?superTforconsumers(writing);2.Typeerasureremovesgenerictypeinformationatruntime,pre

Aug 25, 2025 am 10:02 AM

java Generics

Solve Spring JPA foreign key constraint creation error: Correct handling of composite primary keys

This article aims to help developers resolve foreign key constraint creation errors encountered when mapping database tables with composite primary keys using Spring JPA. Through the example code, we explain in detail how to define a composite primary key class and use it correctly in the entity class, and finally successfully create a foreign key relationship, avoiding the number of referencing and referenced columns for foreign key disagree errors.

Aug 25, 2025 am 10:00 AM

Value-based sorting: Solve the problem of key-value conflict in TreeMap

This article explores the problem of data loss due to Comparator treating different keys as equal when sorting Java TreeMaps based on values ??using a custom Comparator. We will analyze the cause of the problem and provide solutions to ensure that all key-value pairs are properly retained in the sorted map. At the same time, we will also notice the potential risks of null pointer exceptions and provide a safer Comparator implementation.

Aug 25, 2025 am 09:54 AM

Solve the problem of Selenium Chromedriver path recognition in IntelliJ

This article aims to solve the common IllegalStateException when running Selenium tests in IntelliJ IDEA, that is, the system cannot find the ChromeDriver driver path. Although the user may have set the webdriver.chrome.driver system properties correctly, the error persists. The core solution is to ensure that all necessary Selenium library files (including the JAR packages in the lib subdirectory and their parent directory) are correctly added to the IntelliJ project's module dependencies, thereby solving driver loading failures caused by incomplete classpath configuration.

Aug 25, 2025 am 09:51 AM

OptaPlanner Overconstraint Planning: Understanding and applying virtual value policies

This article explores two core strategies of OptaPlanner when dealing with overconstrained planning scenarios: utilizing nullable=true and introducing "virtual values". We will analyze the working principles, applicable scenarios, configuration methods and constraint design of these two methods in detail, aiming to help developers effectively solve the problem of insufficient resources according to actual business needs and achieve optimal or suboptimal planning results.

Aug 25, 2025 am 09:45 AM

Detailed explanation of Micronaut declarative client exception handling configuration

This article details how to use the exceptionOnErrorStatus configuration item in Micronaut declarative client and explains its behavior differences in different scenarios. Through instance code and test cases, we explain how to correctly configure and handle exceptions of declarative clients, avoid common misunderstandings and errors, and help developers better understand and use Micronaut's declarative client functions.

Aug 25, 2025 am 09:39 AM