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What is the Proxy pattern?

TheProxypatternisusedtocontrolaccesstoanobjectandaddfunctionalitywithoutmodifyingtheobjectitself.1.Itsupportslazyinitializationbycreatingtherealobjectonlywhenneeded.2.Itenforcesaccesscontroltorestrictunauthorizedmethodcalls.3.Itenablesloggingormonito

Jun 29, 2025 am 12:42 AM

Design Patterns proxy mode

What is `FileOutputStream`?

FileOutputStreaminJavawritesbytedatatofiles.Itconnectstoafile,enablingdirectbytewriting,creatingthefileifitdoesn'texist,oroverwritingitbydefaultunlessappendmodeisused.1.Worksbestforbinarydatalikeimagesorserializedobjects.2.UseOutputStreamWriterwhenha

Jun 29, 2025 am 12:39 AM

What is the dependency inversion principle? (Rephrased)

The two core views of DIP are: high-level modules should not rely on low-level modules, both should rely on abstraction; abstraction should not rely on details, details should rely on abstraction. Specifically, 1. High-level modules (such as service classes) should not directly rely on specific low-level components (such as database tools), but should be decoupled through interfaces or abstract classes; 2. Abstract (such as interfaces) should be the core of dependencies, and specific implementations should be adapted based on abstractions. This design can improve code testability, enable more flexible replacement and clear separation of concerns. When applying, you need to: 1. Identify key components that have direct dependencies in the system; 2. Define interfaces for these dependencies; 3. Modify dependency classes to use interfaces instead of specific types; 4. Implement interfaces in actual classes. Common misunderstandings include: abstraction for the sake of abstraction,

Jun 29, 2025 am 12:34 AM

What is JIT compiler?

AJITcompilerimprovesruntimeperformancebycompilingcodeduringexecution.Itworksbyfirstinterpretingcode,detectingfrequentlyusedsectionscalled“hotspots,”compilingthosesectionsintomachinecodeonthefly,andcachingthecompiledcodeforreuse.Itiswidelyusedinenviro

Jun 29, 2025 am 12:23 AM

translater jit compiler

What is method overriding?

Method overriding is a subclass providing a concrete implementation of the defined method of the parent class, changing behavior by keeping the same name and parameters. ① Method rewriting makes the code more flexible. For example, the area() method of the Shape base class can be rewritten by Circle and Square subclasses to realize their respective calculation methods; ② Rewriting requires that the subclass method has the same name, the same return type, and the same parameters as the parent class. Python does not require special keywords, and Java/C# is annotated with @Override/override; ③ Applicable to the use of final/sealed methods or irrelevant logic when subclasses in the inheritance system require different behaviors; ④ Notes include not changing signatures to cause overloading, forgetting to call the parent class method, the inability to rewrite private methods, and language differences.

Jun 29, 2025 am 12:12 AM

What are atomic variables?

Atomic variables are variables used to avoid data competition in multithreaded environments. Because when multiple threads access and modify normal variables at the same time, unpredictable behavior, such as value errors, crashes or logical errors, when using atomic variables at this time, each operation will be completed in a single indivisible step, ensuring thread safety. Typical uses include cross-thread counting, flag signaling, and simple state sharing. Its implementation relies on special CPU instructions (such as comparison exchange, addition atomic operations), and provides encapsulation types at the language layer, such as Java's AtomicInteger, C's std::atomic, Go's atomic.Int64, etc. Suitable for replacing mutex locks in scenarios that are sensitive to performance and simple to operate

Jun 29, 2025 am 12:04 AM

What is a `Semaphore`?

Semaphore is a synchronization mechanism used to control concurrent access. Its core role is to limit the number of threads accessed simultaneously to avoid resource competition and system overload. It manages resource access by issuing a "pass". Before accessing the resource, threads need to call acquire() to obtain permission, and call release() to return the permission after use. Unlike Lock, Semaphore allows multiple threads to access resources at the same time, which is suitable for resource pool management, flow control, current limiter, and coordinate thread execution sequence. When using it, you should pay attention to the initial license setting, ensure that release() is executed correctly, select appropriate synchronization tools (such as Lock is recommended for mutex scenarios), and use try-fi

Jun 28, 2025 am 01:49 AM

What is auto boxing and unboxing?

AutoboxingandunboxinginJavaarefeaturesthatautomaticallyconvertbetweenprimitivetypesandtheirwrapperclasses.Autoboxingconvertsprimitivestowrapperobjects,suchasinttoInteger,commonlyusedwhenstoringprimitivesincollectionsorpassingthemtomethodsrequiringobj

Jun 28, 2025 am 01:46 AM

What is the Builder pattern?

Builder mode is used to build complex objects, suitable for scenarios with multiple steps or optional components. 1. Separate structure and representation. 2. Hide internal construction logic. 3. Control the order of steps through Director. Avoid using simple objects or when multiple variations are not required.

Jun 28, 2025 am 01:43 AM

Difference between abstract class and interface?

Abstractclassescancontainimplementedlogic,constructors,andnon-staticfields,whileinterfacesdefinecapabilitieswithoutimplementation.1.Abstractclassesallowpartialimplementationandaccesscontrol.2.Interfacessupportmultipleinheritanceanddefaultmethodsbutla

Jun 28, 2025 am 01:42 AM

java

How to use if-else if-else?

When using the if-elseif-else structure, you should pay attention to the following points: 1. The order of condition judgment must be reasonable, and conditions with high priority should be placed in front to ensure the correct logic; 2. Avoid too deep nesting, and keep the code concise by returning or splitting functions in advance; 3. Else branches are not necessary and can be omitted when there is no processing; 4. Use && and || to simplify the combination of multiple conditions to improve the readability of the code. Following these methods can make the judgment of conditions clearer and more efficient.

Jun 28, 2025 am 01:41 AM

What is the Adapter pattern?

TheAdapterpatternsolvestheproblemofincompatibleinterfacesinsoftwaredevelopmentbyactingasabridgebetweenthem.Itallowsexistingclassesorthird-partylibrarieswithmismatchedinterfacestoworkseamlesslywithinasystemwithoutmodifyingtheiroriginalcode.Forexample,

Jun 28, 2025 am 01:41 AM

What is covariant return type?

Covariant return types allow subclasses to use more specific return types when rewriting parent class methods, improving code readability and polymorphic support. The core points are as follows: 1. It makes the return type of the subclass method more specific than the parent class (such as Dog instead of Animal); 2. It is available in Java 1.5 and C, but C#, Python, and JavaScript are not directly supported; 3. It is often used in factory methods, smooth interfaces and other scenarios to reduce casting; 4. When using it, it is necessary to ensure that there is an inheritance relationship between the return type and is not suitable for basic types and generic erasing environments.

Jun 28, 2025 am 01:39 AM

What is connection pooling?

Connection pooling improves performance by reusing database connections. It avoids frequent creation and destruction of connections, reduces latency, reduces server load, and prevents connection limits from being exceeded during peak traffic. Its working principle is: when applying the requested connection, if there is an available and matching connection in the pool, it will be returned directly, otherwise a new connection will be created; after use, the connection is marked as available rather than closed. Commonly found in Web applications and microservice architectures, such as Django, RubyonRails, Node.js and other frameworks. Pay attention to pool size configuration, idle connection timeout and connection leakage issues.

Jun 28, 2025 am 01:39 AM