av人摸人人人澡人人超碰妓女,9999国产精品欧美久久久久久

Article Tags

Home

Technical Articles

Java

javaTutorial

What is a weak reference?

Weak references are a method that points to an object without increasing its reference count, which is mainly used to avoid memory leaks caused by circular references or unnecessary object retention. It is suitable for situations where you want to attach information to objects that have no control over their life cycle, such as cache systems, event listener registrations, and mapping additional data without having to own object ownership. In Python, weak references can be created through the weakref module, for example, using weakref.ref(obj); when the original object is deleted, the weak reference will return None. Not all objects support weak references. Some built-in types such as list or dict need to be explicitly enabled, while primitive types such as integers or strings may show different behaviors due to the internal caching mechanism. Pay attention to when using:

Jun 26, 2025 am 12:57 AM

What are intermediate stream operations?

IntermediatestreamoperationsinJavaaremethodsthattransformorfilterdatawithoutproducingafinalresult.Theseoperations,suchas1.filter(),2.map(),3.sorted(),4.limit(),5.skip(),and6.distinct(),returnanewStream,enablingmethodchaining.Theyarelazyandonlyexecute

Jun 26, 2025 am 12:56 AM

How to read a file in Java?

There are three common ways to read files in Java. First, use BufferedReader to read line by line, which is suitable for large files. The steps include creating a FileReader, wrapping it into a BufferedReader, reading and closing the stream with readLine(); Second, use Files.readAllLines() to read the content of the small file into the list at one time; Third, use Scanner to read and parse the data as needed, which is suitable for structured text. In addition, pay attention to issues such as path setting, resource closing and encoding specification. The selection method should be determined based on specific needs such as file size and processing methods.

Jun 26, 2025 am 12:48 AM

What is tight coupling vs loose coupling?

Tight coupling refers to the existence of a strong dependency between modules, such as the class directly instantiates another concrete class, resulting in multiple adjustments required to modify one place; loose coupling refers to reducing dependencies through interfaces, abstract classes, etc., improving flexibility and maintainability. 1. The phenomenon of tight coupling includes directly instantiating specific classes, calling dependency specific implementations, and altering involves multiple modules; 2. The loose coupling implementation methods include using interfaces or abstract classes, dependency injection, event-driven communication, and API calls to replace direct references; 3. Selection based scenarios: tight coupling is suitable for small projects, performance sensitive, and module stability, and loose coupling is suitable for complex systems, team collaboration, and scenarios that require flexible expansion.

Jun 26, 2025 am 12:43 AM

Why use generics?

The core role of generics is to solve the problems of code reuse and type safety. 1. Improve code reusability: Only once can you write logic through generics to adapt to multiple types, such as function identity(value:T):T can handle any type input; 2. Ensure type safety: Compared with any type, generics ensure that the incoming and return type are consistent, such as function firstElement(arr:T[]):T|undefined can accurately deduce array element types; 3. Better development experience: generics combine with IDE to provide automatic completion and type prompts, such as encapsulating request function fetchData(url:string):Promise can clearly return structures, improving development efficiency.

Jun 25, 2025 pm 06:22 PM

Generics Generics

How to monitor JVM performance?

Monitoring JVM performance requires paying attention to core indicators such as memory, GC, threading and class loading. 1. Use built-in tools such as jstat, jmap, jstack to quickly troubleshoot problems, such as jstat-gc1000 to view GC frequency and time consumption in real time; 2. Use VisualVM, JConsole or Prometheus Grafana to perform visual monitoring, centrally display key indicators and facilitate team collaboration; 3. Set an alarm mechanism to pay attention to heap memory usage, GC pause time, thread status and class loading number, and promptly detect exceptions; 4. Combine GC log analysis and heapdump, thread snapshot and other information to locate performance bottlenecks and gradually optimize.

Jun 25, 2025 pm 06:05 PM

monitor jvm performance

What is a thread in Java?

AthreadinJavaisthesmallestunitofexecutionthatallowsconcurrentoperations,enhancingapplicationresponsivenessandefficiency.Itrunscodeindependentlyfromthemainprogram,enablingtaskslikebackgroundprocessingandmultitasking.Javaprogramsstartwithamainthread,bu

Jun 25, 2025 pm 06:03 PM

Multithreading java thread

Why use the `synchronized` keyword?

The synchronized keyword is used to ensure that the access to shared resources in a multi-threaded environment is thread-safe. 1. It prevents multiple threads from executing the same piece of code at the same time by locking objects or classes, thereby avoiding the problems of race conditions and data inconsistency; 2. It prevents memory consistency errors, forces threads to read and write data from main memory, and ensures visibility between threads; 3. It automatically manages the acquisition and release of locks, simplifies lock control in concurrent programming, and is suitable for most simple mutually exclusive scenarios.

Jun 25, 2025 pm 05:14 PM

Thread safety

What are the different wrapper classes?

The wrapper class in Java encapsulates the basic data type into an object, so that the basic type has object characteristics. Its core uses include: 1. Used for collection frameworks (such as ArrayList, HashMap storage objects); 2. Provide practical methods (such as Integer.parseInt); 3. Support null values ??to represent "no value" state; 4. Used in generics. Java 5 supports automatic boxing and unboxing, but attention should be paid to null pointer exceptions and performance overhead. Common methods include string conversion, obtaining maximum/minimum value, converting to strings and comparing operations, etc., which are commonly found in set operations, generic programming and potentially empty data processing scenarios.

Jun 25, 2025 pm 05:02 PM

java Packaging

What are streams in Java IO?

Java I/O streams are divided into byte streams and character streams, which are used to process binary data and text data respectively. 1. Byte streams read and write data in units of bytes. Common classes include InputStream and OutputStream; 2. Character streams operate text in units of characters. The default is platform encoding. Common classes are Reader and Writer; 3. Common stream classes include FileInputStream/FileOutputStream, BufferedInputStream/BufferedOutputStream, FileReader/FileWriter, BufferedReader/Buffered

Jun 25, 2025 pm 05:01 PM

streams java io

What is `fail-fast` behavior?

Fail-fastbehavior is a design principle that stops and reports immediately when errors are found, used to quickly expose problems to avoid subsequent risks. 1. In programming languages ??and libraries, such as Java's ConcurrentModificationException, Python iterative modification errors, and unit test failures, which helps quickly locate errors. 2. In API design, prevent error spread by verifying parameters as early as possible, such as function limiting the percentage range throws exceptions in advance. 3. Practices such as CI/CD construction failure, front-end form pre-checking, priority writing of unit tests, etc. in the development process can also speed up problem feedback. Although it is not suitable for all scenarios, if you need fault-tolerant online services,

Jun 25, 2025 pm 04:45 PM

Behavior

What is garbage collection root?

The GC root is the starting point for the garbage collector to determine the surviving object, and it traces whether the object is reachable through the reference chain to determine whether it is recycled. The main types include: 1. Local variables; 2. Active threads; 3. Static fields; 4. JNI references. During operation, GC starts from these root nodes to mark all reachable objects, and those that are not marked are collected as garbage. Understanding GC roots can help troubleshoot memory leaks. Common reasons such as unregistered listeners, uncleaned thread local variables, or continuously growing static collections can be discovered and resolved by analyzing the root path.

Jun 25, 2025 pm 04:37 PM

Garbage collection Root object

What is the JDK?

JDK (JavaDevelopmentKit) is a software development environment for developing Java applications and applets. It contains tools and libraries required to compile, debug and run Java programs. Its core components include Java compiler (javac), Java runtime environment (JRE), Java interpreter (java), debugger (jdb), document generation tools (javadoc) and packaging tools (such as jar and jmod). Developers need JDK to write, compile Java code and develop with the help of IDE; without JDK, Java applications cannot be built or modified. You can enter javac-version and java-version in the terminal

Jun 25, 2025 pm 04:05 PM

java jdk

What is the difference between composition and aggregation?

The difference between Composition and aggregation is the tightness of association between objects. 1. Composition is a strong "ownership" relationship. The child object cannot exist independently of the parent object, such as car and engine, life cycle binding, and is represented by a solid diamond in UML; 2. Aggregation is a weak "ownership" relationship, and the child object can exist independently, such as department and teacher, life cycle not bound, and is represented by a hollow diamond in UML; 3. When selecting a combination, if the part leaves the whole and is meaningless or needs to control its life cycle, such as windows and borders; 4. When selecting aggregation, if the part can exist independently and needs to be shared flexibly, such as school and students. The key to judging is whether the sub-object can exist independently.

Jun 25, 2025 pm 03:57 PM

combination polymerization