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What is a design pattern?

Adesignpatternisareusablesolutiontocommonsoftwaredesignproblems,notafinishedproductorspecificcode.Itservesasatemplatethathelpsdeveloperscreateflexible,maintainable,andscalablecode.1.Designpatternsimprovecommunicationthroughsharedterminology.2.Theyspe

Jun 26, 2025 am 01:17 AM

Design Patterns software design

How does garbage collection work?

Garbage collection (GC) is a mechanism for automatically managing memory in a programming language that recognizes and frees memory that is no longer occupied by objects that are no longer used by programs. It realizes memory recycling through reference counting, mark-clearing, copy algorithms and generational collection. Each algorithm has its own advantages and disadvantages: 1. The reference counting method is simple but cannot handle circular references; 2. The mark-clearing method solves circular reference problems but may produce fragments; 3. The copy algorithm is efficient but wastes half of the memory; 4. Generational collection optimizes recycling strategies based on objects in different life cycles. GC may cause performance fluctuations and memory leaks in actual applications, and can optimize behavior through parameter configuration. Methods to reduce GC pressure include avoiding frequent creation of short-lived objects, using object pools, rationally utilizing weak references, and monitoring

Jun 26, 2025 am 01:16 AM

How to use `LocalDate`?

When using LocalDate to process dates, first obtain the current date with LocalDate.now(), and if you want to specify the time zone, use LocalDate.now(ZoneId.of("Asia/Shanghai")); secondly, you can use LocalDate.of(1990,5,15) or LocalDate.of(1990, Month.MAY,15) to improve readability; common operations include adding and subtracting days such as plusDays(), and judging the date before and after such as isBefore(); note that if there are immutable objects, you need to reassign them, and use DateTimeFormatte to format them.

Jun 26, 2025 am 01:15 AM

What is dependency inversion principle?

TheDependencyInversionPrinciple(DIP)statesthathigh-levelmodulesshouldnotdependonlow-levelmodules;bothshoulddependonabstractions.1)DIPreducestightcouplingbyhavingcoderelyoninterfacesorcontractsratherthanspecificimplementations,makingsystemsmoreflexibl

Jun 26, 2025 am 01:15 AM

Design Principles Dependency inversion

What is the `throws` keyword?

ThethrowskeywordinJavaisusedtodeclarecheckedexceptionsthatamethodmaythrow,passingtheresponsibilityofhandlingthemtothecaller.1.Itallowsamethodtospecifywhichexceptionsitdoesnothandle,requiringthecallertoeithercatchthemorpropagatethemfurther.2.Itisusede

Jun 26, 2025 am 01:14 AM

What is the diamond operator ``?

The diamond operator is used to simplify the instantiation of generic classes in Java. 1. Improve code readability and avoid repeated declaration of types; 2. The compiler can automatically infer types, which is suitable for collection creation, custom generic classes and method chain calls; 3. Manually specify the type when complex overloading or return types are fuzzy; 4. It is recommended to define a complete generic type and use tools to check type inference.

Jun 26, 2025 am 01:11 AM

java Diamond operator

How to create a custom exception?

Custom exceptions are implemented in Python by inheriting the Exception class or its subclasses, which are used to improve code readability and targeted error handling. When built-in exceptions cannot meet specific business needs, for example, you need to distinguish between multiple user input error scenarios, you can create different exception types such as InvalidEmailError and PasswordTooShortError. The creation method is simple. You only need to define a new class. You can also add initialization parameters such as message and error_code to provide more information to assist in debugging. Suitable scenarios for using custom exceptions include modular projects, business rule verification, and third-party library development, such as the data parsing module that defines ParseError

Jun 26, 2025 am 01:11 AM

Difference between Statement and PreparedStatement?

The core difference between Statement and PreparedStatement is security, performance, and maintainability. 1. In terms of security, PreparedStatement uses parameterized queries to prevent SQL injection, while Statement directly splicing strings is vulnerable to attack; 2. In terms of performance, PreparedStatement precompiled and caches SQL, making repeat execution more efficient; 3. In terms of maintainability, PreparedStatement has a clearer parametric writing structure, which is easy to maintain; 4. It is recommended that PreparedStatement be used first in scenarios involving user input or frequent execution, and Statement can be used in simple scripts.

Jun 26, 2025 am 01:09 AM

Difference between synchronized method and block?

Synchronizedblocksaregenerallybetterwhenyouneedfine-grainedcontrol,flexibilityinchoosinglockobjects,andimprovedperformancebylockingonlycriticalsections.1.Synchronizedmethodslocktheentiremethodandusetheobjectorclassasthelock,leadingtobroaderlockingtha

Jun 26, 2025 am 01:07 AM

How to access array elements?

The key to accessing array elements is to master the index usage and language syntax habits. 1. The index usually starts from 0 and obtains data through position number, such as fruits[0], which represents the first element; 2. Negative indexes can represent the end element, such as Python fruits[-1]; 3. Accessing the out-of-bounds index may report an error or return an uncertain value, so you need to pay attention to boundary judgment; 4. It can traverse the array by batch processing elements, such as for loops, foreach and other methods, such as JavaScript for loops or forEach functions; 5. Multi-dimensional arrays need to use multiple indexes to access nested elements, such as Python matrix0, which represents the second element on the first line. There may be differences in syntax of different languages, and the document should be used as

Jun 26, 2025 am 01:06 AM

What is the ServiceLoader API?

ServiceLoaderinJavadynamicallyloadsserviceimplementationsatruntimebyscanningMETA-INF/servicesfiles.1.Itdecouplescodefromspecificimplementations.2.ItscansJARsforconfigurationfileslistingimplementationclasses.3.Itusesthecontextclassloadertoinstantiatet

Jun 26, 2025 am 01:06 AM

What is `CompletableFuture`?

CompletableFutureinJavasimplifiesasynchronousprogrammingbyenablingnon-blockingcodewithgreaterflexibilitythanthetraditionalFutureinterface.1.Itallowsmanualcompletionoftasksusingcomplete(),2.supportsasyncexecutionviarunAsync()orsupplyAsync(),3.enablesc

Jun 26, 2025 am 01:05 AM

What are default methods in interfaces?

The default method allows methods with implementations to be defined in Java interfaces, and default keyword is modified by default, solving the problem of destroying existing implementations when interface extensions. For example, if the stream() method is added to the Collection interface, if it is abstract, all subclass implementations are required, and the default method allows it to be automatically inherited. When multiple interfaces contain the same default method, the specified call needs to be manually rewrite, such as using A.super.sayHello() to explicitly select implementation. Its main application scenarios include collection framework enhancement, providing optional behavior, and simplifying template method patterns, but abuse should be avoided to prevent interface bloat.

Jun 26, 2025 am 01:03 AM

Why use the `Serializable` interface?

ImplementingtheSerializableinterfaceinJavaallowsaclasstobeconvertedintoabytestreamforstorageortransmission.Asamarkerinterfacewithnomethods,itsignalsthattheclassisreadyforserialization,enablingmechanismslikeObjectOutputStreamtoprocessit.Failingtoimple

Jun 26, 2025 am 01:02 AM

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