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A Deep Dive into Java HashMap and Its Performance

HashMap is implemented in Java through array linked lists/red and black trees. Its performance is affected by the initial capacity, load factor, hash function quality and the immutability of the keys; 1. Use (n-1)&hash to calculate the index to improve efficiency; 2. When the linked list length exceeds 8 and the number of buckets is ≥64, it will be converted to a red and black tree, so that the worst search complexity is reduced from O(n) to O(logn); 3. Rehash all elements when expanding, the overhead is high, and the capacity should be preset; 4. The key must be rewrite hashCode and equals correctly; 5. ConcurrentHashMap should be used in multi-threaded scenarios; the average time complexity is O(1) under reasonable use, but improper use will lead to performance degradation.

Aug 01, 2025 am 05:54 AM

Mastering Dependency Injection in Java with Spring and Guice

DependencyInjection(DI)isadesignpatternwhereobjectsreceivedependenciesexternally,promotingloosecouplingandeasiertestingthroughconstructor,setter,orfieldinjection.2.SpringFrameworkusesannotationslike@Component,@Service,and@AutowiredwithJava-basedconfi

Aug 01, 2025 am 05:53 AM

java dependency injection

Modern Java Build and Dependency Management with Maven and Gradle

Mavenisidealforstandardized,enterpriseenvironmentswithitsXML-based,convention-over-configurationapproach,while2.GradleexcelsinflexibilityandperformanceusingGroovyorKotlinDSL,makingitbetterforcomplex,large-scale,orAndroidprojects,3.bothsupportrobustde

Aug 01, 2025 am 05:25 AM

Optimizing Java Performance: A Guide to Garbage Collection Tuning

Choosing the right garbage collector and configuring it properly is the key to optimizing Java application performance. First, select the GC type according to application needs: SerialGC is used for small memory applications, ParallelGC is used for high throughput scenarios, G1GC is used for large memory and controllable pauses, and ZGC is used for ultra-low latency requirements (such as financial transactions). 1. Set the heap size reasonably to avoid being too large or too small. It is recommended that -Xms and -Xmx are equal to -Xmx to prevent dynamic expansion; 2. For G1GC, you can set the target pause time through -XX:MaxGCPauseMillis, adjust -XX:G1HeapRegionSize to deal with large objects, and use -XX:InitiatingHea

Aug 01, 2025 am 05:12 AM

Garbage collection java performance

Exploring Virtual Threads in Java with Project Loom

VirtualthreadsinJava—introducedaspartofProjectLoom—areagame-changerforwritinghigh-throughput,concurrentapplicationswithouttheusualcomplexityofasyncprogrammingorthreadpooling.Ifyou’veeverstruggledwithblockingI/Ooperationss

Aug 01, 2025 am 05:03 AM

java 虛擬線程

How to perform a deep copy of an object in Java?

To implement deep copy in Java, new objects must be created and all nested objects recursively copy to avoid sharing mutable states. The specific methods include: 1. Manual deep copy using copy constructor. The advantages are type safe and controllable, and the disadvantages are cumbersome and error-prone; 2. Use serialization to achieve deep copy through byte streams, which can automatically process complex objects but require all classes to achieve Serializable and have low performance; 3. Use ApacheCommonsLang's SerializationUtils to simplify the serialization process, but is also limited by Serializable requirements; 4. Use JSON libraries such as Gson or Jackson to serialize objects to JSON and deserialize them, which is suitable for non-Se

Aug 01, 2025 am 05:01 AM

java deep copy

How to write to a file in Java safely?

Use try-with-resources to ensure automatic shutdown of resources; 2. Explicitly specify UTF-8 encoding to ensure text compatibility; 3. Call flush() and sync() on key data to prevent data loss; 4. Use Files.write() to handle simple writes, safe and concise; 5. Check file paths and permissions in advance to avoid write conflicts; 6. Always capture and properly handle IOException to ensure the robustness of program. The above methods jointly ensure the security of Java file writing.

Aug 01, 2025 am 04:51 AM

java file writing

Effective Java Patterns: When to Use Records vs Classes

Records are used when the data is immutable, only used to carry data without complex behavior; 2. Classes are used when encapsulation, mutable state, inheritance or verification logic is required; 3. Avoid adding instance fields to records or destroying immutability; 4. Records are suitable for DTO and return value encapsulation, and classes are suitable for scenarios containing business logic or life cycle management; 5. If the object is only data aggregation, use records, and if it is a behavioral object, use classes.

Aug 01, 2025 am 04:40 AM

java programming

What's New in Java 21: A Comprehensive Developer's Guide

Java21,releasedinSeptember2023,isalong-termsupport(LTS)versionthatintroducesmajorimprovementsfordevelopersandenterprises.1.VirtualThreadsarenowfinal,enablinghigh-throughputconcurrencywithsimple,synchronous-stylecode,drasticallyreducingthecomplexityof

Aug 01, 2025 am 04:31 AM

new features Java 21

Java Concurrency Utilities: ExecutorService vs CompletableFuture

ExecutorService is suitable for simple task submission and thread resource management, but does not support non-blocking callbacks and task combinations; 2. CompletableFuture supports rich asynchronous orchestration operations, such as chain calls, task combinations and exception handling, which are suitable for complex asynchronous processes; 3. The two can be used in combination. It is recommended to use CompletableFuture to implement asynchronous logic, and cooperate with custom ExecutorService to control execution resources to achieve efficient and maintainable concurrent programming.

Aug 01, 2025 am 04:26 AM

Thread Dumps Analysis for Java Applications

Acquisition of thread dumps can be collected multiple times through jstack, kill-3, JConsole or SpringBootActuator and other methods; 2. In the thread state, RUNNABLE may correspond to high CPU or infinite loops, BLOCKED indicates lock competition, WAITING/TIMED_WAITING is a waiting state, so you need to pay attention to exception accumulation; 3. Deadlock will be clearly indicated by jstack, which is manifested as a loop waiting lock, which should be solved by unified lock sequence or reduced lock granularity; 4. High CPU threads need to combine top and hexadecimal conversion positioning to check whether there are regular backtracking, serialization and other time-consuming operations in the call stack; 5. A large number of BLOCKED threads point to the same lock object to indicate lock competition

Aug 01, 2025 am 04:24 AM

The Ultimate Guide to Java Exception Handling

Javaexceptionhandlingensuresrobustandmaintainableapplicationsbyproperlymanagingruntimeerrors.1.TheThrowableclassistheparentofallexceptions,withErrorforJVM-levelissueslikeOutOfMemoryErrorandExceptionforrecoverableconditions.2.Checkedexceptions(e.g.,IO

Aug 01, 2025 am 03:50 AM

java Exception handling

Java Message Service (JMS) with ActiveMQ Tutorial

JMSwithActiveMQenablesasynchronous,looselycoupledcommunicationinenterpriseapplicationsbyusingmessaging;thistutorialdemonstratessettingupActiveMQandimplementingapoint-to-pointmessagingexampleusingtheJMSAPI.1.JMSisaJavaAPIsupportingtwomodels:Point-to-P

Aug 01, 2025 am 03:42 AM

Securing REST APIs with Spring Security and Java

Disable sessions and CSRF, use SessionCreationPolicy.STATELESS and csrf().disable() to achieve REST-friendly and secure; 2. Use JWT for stateless authentication, generate and verify tokens containing user roles and expiration time through JwtUtil; 3. Create a JwtAuthenticationFilter to intercept requests, parse the Bearer token in the Authorization header, and store the authentication information into the SecurityContextHolder after verification; 4. Use @PreAuthorize("hasRole('ADMIN')"

Aug 01, 2025 am 03:31 AM