高清精品国内视频,成人网站免费看黄a站视频

Article Tags

Home

Technical Articles

Java

What are Java Records (Java 14 )?

JavaRecord is a feature used to simplify data class declarations, introduced from Java 14. It automatically generates constructors, getters, equals, hashCode and toString methods, which are suitable for DTO, model classes, multi-return value encapsulation and other scenarios; it is not suitable for situations where inheritance, mutable state or complex logic is required. Notes include: default is final class and fields, support for adding methods and static fields, and Java16 supports pattern matching. For example, recordPerson(Stringname,intage){} can replace the traditional POJO class and improve the simplicity and maintenance of the code.

Jul 05, 2025 am 01:58 AM

Java 14

How does HashMap collision resolution work in Java?

HashMap handles collisions mainly through chain storage. When multiple keys are mapped to the same index, they will be stored in the linked list or tree at that location. 1. HashMap uses hashCode() method to calculate the hash value of the key and determine the index in the array through internal logic; 2. When different keys produce the same index, they are linked to conflicting items in the form of a linked list; 3. If the length of the linked list exceeds 8, it will be automatically converted to a red and black tree to improve performance; 4. When the number of elements exceeds the product of the load factor and capacity, HashMap will double the capacity and reassign all entries, reducing the probability of collision but bringing certain performance overhead.

Jul 05, 2025 am 01:57 AM

How to create threads in Java programming?

There are two main ways to create threads in Java: inherit the Thread class and implement the Runnable interface. 1. To inherit the Thread class, you need to define a subclass and overwrite the run() method, and start a thread through start(), which is suitable for simple tasks but is limited by the Java single inheritance mechanism; 2. To implement the Runnable interface to separate tasks from threads, run Runnable instances through Thread, support more flexible design and can be used in combination with thread pools; in addition, Java8 can also use Lambda expressions to simplify the writing of one-time tasks. Be careful not to call run() directly, avoid repeated starts, reasonably naming threads, and understand the priority scheduling mechanism.

Jul 05, 2025 am 01:48 AM

java thread Thread creation

How does Java Garbage Collection work?

Garbage collection (GC) is the core mechanism of Java's automatic memory management, used to identify and free objects that are no longer in use to avoid memory leaks. 1. Garbage objects refer to objects that are no longer referenced by any root object; 2. The basic process of GC includes marking surviving objects and recycling unlabeled objects; 3. Common garbage collectors include SerialGC, ParallelScavenge, CMS, G1, ZGC/Shenandoah, which are suitable for different scenarios; 4. Methods to optimize GC performance include reasonably setting the heap size, selecting appropriate algorithms, monitoring logs, avoiding memory leaks, and reducing temporary object generation. By understanding the GC mechanism, code efficiency and system tuning capabilities can be improved.

Jul 05, 2025 am 01:43 AM

java Garbage collection

Preventing and Diagnosing Java Memory Leaks

To prevent and diagnose memory leaks in Java, the core method is "early detection and early processing". 1. First of all, you need to understand common scenarios: such as the static collection class not being released, the listener not being logged out, the cache not being invalidated, and the use of ThreadLocal improperly. 2. Secondly, use tools to assist detection, such as VisualVM preliminary positioning, MAT analysis heapdump, YourKit/JProfiler in-depth analysis, and JConsole observes memory trends. 3. In daily development, we should avoid long-term holding of useless objects, using weak references, using ThreadLocal reasonably and removing timely, logging out the listener after registration, unit test simulation to simulate long-term operation, and setting appropriate JVM parameters to enable GC logs

Jul 05, 2025 am 01:39 AM

How does Java Garbage Collection Work Internally?

Java's garbage collection mechanism manages memory by automatically identifying and cleaning up objects that are no longer in use. GC mainly operates in heap memory, divided into the new generation (including the Eden area and the Survivor area), the old age and the metaspace; common GC algorithms include mark-clear, copy and mark-collation, which are used to solve the memory recovery problems of different generations respectively; GC triggering timings include MinorGC (Eden area full time) and MajorGC/FullGC (when the old age is insufficient or when the System.gc() is called), explicit calls should be avoided; GC performance can be monitored and optimized through JVM parameters, logs and tools such as jstat, VisualVM, and MAT. Reasonable setting of the heap size and selecting the GC algorithm will help improve

Jul 05, 2025 am 01:29 AM

Understanding thread pools in Java ExecutorService.

Thread pools are the core mechanism used to manage threads in Java concurrent programming. Their role is to avoid the performance overhead caused by frequent creation and destruction of threads. 1. It improves response speed and resource utilization by pre-creating a set of threads and waiting for task allocation; 2. It is suitable for handling a large number of short life cycle and highly repetitive tasks, such as network requests or timing tasks; 3. Java provides a variety of thread pool types, including FixedThreadPool (suitable for heavy load systems), CachedThreadPool (suitable for short-term asynchronous tasks), SingleThreadExecutor (suitable for task serial execution) and ScheduledThreadPool (suitable for timing and periodicity)

Jul 05, 2025 am 01:21 AM

Thread Pool

Efficiently Using Java Streams for Data Processing

Five points to pay attention to when using JavaStreams: 1. Intermediate operations (such as filters, maps) must be executed through terminal operations (such as collect, forEach), otherwise it will not take effect; 2. Avoid modifying external variables in intermediate operations to prevent concurrency problems; 3. Select the terminal operation type according to the scene, such as anyMatch to judge existence more efficiently; 4. Parallel flows are suitable for complex operations in large data volumes, while small data actually increases overhead and is sensitive to sequence; 5. Reduce object creation and packing, and give priority to basic flows such as IntStream to improve performance.

Jul 05, 2025 am 01:16 AM

What are non-primitive data types?

Non-primitive data types are not built into the programming language, but are complex structures created by programmers or libraries. 1. Arrays are used to store multiple values ??of the same type, accessed through indexes, and their size is fixed or dynamically adjustable; 2. Classes and objects allow the construction of custom structures, using classes as blueprints to create objects with attributes and methods; 3. Strings are character sequences, which are non-primitive types in some languages ??and support method calls; 4. Advanced types such as collections, such as lists, mappings, and collections, provide more complex data operation functions.

Jul 05, 2025 am 01:15 AM

Java JDBC: Connecting to Relational Databases

To correctly connect to the database through JDBC, first introduce the driver package of the corresponding database, such as MySQL's mysql-connector-java; secondly, use the correct URL format, such as jdbc:mysql://localhost:3306/mydb, and pay attention to the correctness of parameters, hostname and port; then write code to obtain connections and handle exceptions, it is recommended to use configuration files to store username and password, and capture SQLException to provide meaningful prompts; finally be sure to close the connection resources, and it is recommended to use try-with-resources to automatically manage it. Follow these steps to effectively avoid common problems and ensure stable connections.

Jul 05, 2025 am 01:11 AM

Database Connectivity

Checked vs unchecked exceptions in Java explained.

Checked exceptions are exceptions that must be processed during compilation, such as IOException and SQLException, which need to be declared by try-catch or throws, otherwise an error will be reported in the compilation; non-checked exceptions are runtime exceptions, such as NullPointerException and ArrayIndexOutOfBoundsException, which the compiler does not force processing. 1. Checkedexception is suitable for errors that the caller must handle, such as the IO operation fails, suitable for scenarios where recovery, retry or explicit processing is required; 2.unchec

Jul 05, 2025 am 12:47 AM

Java Logging frameworks comparison (e.g., Log4j2, SLF4J, Logback).

SLF4J is a log interface, and Logback and Log4j2 are implementation frameworks; 1. SLF4J is a unified interface, providing decoupling capabilities, which facilitates the later replacement of the underlying log system; 2. Logback is developed by the SLF4J author, fast startup, good performance, natural integration, flexible configuration, suitable for SpringBoot projects; 3. Log4j2 has powerful functions, outstanding asynchronous logging performance, suitable for high-concurrency scenarios, but complex configuration and attention to security vulnerabilities; Selection suggestions: SpringBoot uses Logback by default, Log4j2 is selected for high-performance requirements, and SLF4J is required for code decoupling. Old projects can be considered for upgrading or migration.

Jul 05, 2025 am 12:37 AM

Log Framework

Explain Dependency Injection in Java frameworks like Spring.

Dependency injection (DI) is a design pattern that enables loose coupling of code by externally managing dependencies of objects. Its core lies in injecting object dependencies from the outside rather than internal creation, thereby improving flexibility and maintainability. For example, in the UserService, pass into the UserRepository instance through the constructor, that is, the constructor injection. Spring framework supports multiple injection methods through IoC containers: 1. Constructor injection, suitable for forced dependencies; 2. Setter injection, suitable for optional dependencies; 3. Field injection (@Autowired), using annotations directly in fields. Advantages of DI include: decoupling, enhanced testability, flexible configuration, and easy maintenance. In practical applications, you need to pay attention to: avoid

Jul 05, 2025 am 12:29 AM

What is the difference between == and .equals() in Java?

InJava,==comparesobjectreferenceswhile.equals()checksforvalueequality.1.==verifiesiftwovariablespointtothesamememoryinstance,returningfalsefordistinctobjectswithsimilarcontent.2..equals()evaluateslogicalequalitybasedonvalues,butreliesonpropermethodov

Jul 04, 2025 am 02:56 AM