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What is an instance variable?

An instance variable is a variable defined in a class or outside a method, and belongs to an instance of a class. 1. They are different from class variables, and each instance has an independent copy; 2. They are often declared on the top of the class or before the constructor, and are used to store the data unique to the object; 3. Allocate memory when creating the object and accessed through self.variable_name; 4. Common errors include forgetting to use self, not initializing it in __init__, and misuse of mutable objects to cause data sharing.

Jun 29, 2025 am 01:09 AM

How does a while loop work?

Awhileloopexecutescoderepeatedlyaslongasaconditionremainstrue.1.Itcheckstheconditionbeforeeachiterationandstopswhentheconditionbecomesfalse.2.Itisusefulwhenthenumberofiterationsisunknown,suchaswaitingforuserinputormonitoringstatuschanges.3.Commonpitf

Jun 29, 2025 am 01:07 AM

cycle

What is inheritance?

Inheritance is the process of the transfer of assets, property or rights between generations, usually after someone dies. Its core content includes: 1. Inheritable items are not limited to money and land, but also personal belongings, titles, debts and digital assets; 2. If there is a will, the property shall be distributed according to the will, but the laws of some regions stipulate that some property must be left to immediate relatives; 3. When there is no will, the property shall be distributed to spouses, children or parents according to local laws; 4. During the inheritance process, tax, debts and family disputes should be paid attention to, and legal help is recommended to seek legal help to ensure smooth execution.

Jun 29, 2025 am 01:05 AM

What is Metaspace?

Metaspace is a local memory area introduced by Java 8 for storing class metadata, replacing PermGen to solve memory limitation problems; 1. Metaspace uses local memory instead of heap memory; 2. Supports automatic expansion and no default upper limit; 3. Class metadata is recycled during FullGC or metadata GC; 4. It can be tuned through -XX:MaxMetaspaceSize and -XX:MetaspaceSize; 5. Common monitoring tools include jstat, VisualVM, etc.; 6. Common problems include insufficient memory and metadata leakage, which need to be checked in combination with log and analysis tools.

Jun 29, 2025 am 01:02 AM

What is the NIO package?

NIO is an efficient I/OAPI introduced by Java 1.4. The core advantages are non-blocking IO and buffer-oriented operations; its key components are Buffers (such as ByteBuffer, CharBuffer) and Channel (such as FileChannel, SocketChannel); the non-blocking mode realizes multi-connection processing through Selector to improve system throughput; it is suitable for scenarios such as high concurrent servers and large file transfers; it is more efficient to copy files using FileChannel; when operating Buffers, you need to pay attention to capacity, position, limit status, flip(), clear() and other methods; NIO is not in

Jun 29, 2025 am 01:01 AM

java nio

What is a switch statement?

A switch statement is a control structure that executes different code blocks based on the value of a variable or expression. It works by evaluating the expression and matching multiple case values, and if no match is done, the default branch is executed. Common usages include handling user input, menu selection, and status codes. When using it, you should pay attention to adding break to prevent "through", use default reasonably, and avoid complex conditions. In JavaScript or C, its basic structure is: switch(expression){casevalue1:...break;casevalue2:...break;default:...}. For example, when processing operators in a calculator, Swi can be used

Jun 29, 2025 am 01:00 AM

What is the class loading delegation model?

Java's class loading delegate model is a hierarchical structure mechanism that ensures that classes are loaded by the most trusted class loader. 1. BootstrapClassLoader loads core Java classes (such as java.lang, java.util); 2. ExtensionClassLoader is responsible for loading classes in the extension directory and delegating BootstrapClassLoader; 3. ApplicationClassLoader loads classes in the application classpath and delegates ExtensionClassLoader. When the class needs to be loaded, the request starts from the ApplicationClassLoader and goes up step by step

Jun 29, 2025 am 12:55 AM

What is the transient keyword?

ThetransientkeywordinJavapreventsspecificfieldsfrombeingserialized.1.IttellsJavatoskipserializingmarkedfields,suchassensitivedatalikepasswords.2.Duringdeserialization,transientfieldsaresettotheirdefaultvalues.3.Usecasesincludeenhancingsecurity,managi

Jun 29, 2025 am 12:50 AM

keyword

What is the instanceof operator?

TheinstanceofoperatorinJavaScriptchecksifanobjectisaninstanceofaspecificclassorconstructorfunctionbyexaminingitsprototypechain.1.Itreturnstrueiftheprototypepropertyoftheconstructorexistsintheobject'sprototypechain,asseenwhenjohninstanceofPersonreturn

Jun 29, 2025 am 12:44 AM

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