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What are selectors in NIO?

SelectorsinNIOsolvetheproblemofefficientlymanagingmultipleI/Ochannelswithoutdedicatingathreadtoeachone.1)Theyenableasinglethreadtomonitormanychannelsforreadinessinreading,writing,orotheroperations.2)Thisreducesmemoryandperformanceoverheadcomparedtool

Jun 27, 2025 am 12:53 AM

Difference between JAR WAR and EAR files?

JAR, WAR, and EAR are packaging formats for different purposes in Java. JAR (JavaARchive) is used to encapsulate Java classes, resources and metadata, and is suitable for distribution libraries or independent applications; WAR (WebApplicationARchive) is specially designed for JavaWeb applications, including Servlets, JSPs, etc., and is deployed in Web containers; EAR (EnterpriseApplicationaRchive) is used for complex enterprise applications, and can contain multiple JAR and WAR modules and be deployed in a complete JavaEE server.

Jun 27, 2025 am 12:52 AM

jar war

What is a TreeMap?

ATreeMapvisualizeshierarchicaldatausingnestedrectangleswhereeachrectangle’sarearepresentsavalue.Itisusefulforshowingdatastructureandcomponentproportions,especiallyforlargedatasets.1.Theentiredatasetstartsasonelargerectangle.2.Itsplitsintosmallerrecta

Jun 27, 2025 am 12:50 AM

What is the `==` operator for strings?

In JavaScript, the == operator compares whether the contents of the string value are the same through type casting. When both operands are strings, directly compare the character sequence; if the types are different, convert the type first and then compare. For example, when the string "100" is compared with the number 100, it will be converted to the value 100 for comparison, and the result is true. However, using == may cause unexpected results, such as string objects returning false due to different memory addresses, or case sensitive issues. Therefore, it is recommended to use === strict comparison, requiring that the values ??and types are consistent, and avoid unpredictability caused by type conversion. Common errors include confusing original strings with string objects, ignoring case, and not checking data types. Summary: 1

Jun 27, 2025 am 12:49 AM

What is the JVM?

JVM (Java virtual machine) is the core component of the Java platform. It enables Java programs to run on any device or operating system, realizing "write once, run everywhere". As the running engine of Java applications, JVM loads and converts compiled bytecode into machine code execution; its main components include class loaders, runtime data areas and execution engines; in addition, JVM also supports languages ??such as Kotlin and Scala, and manages memory through automatic garbage collection; common JVM options include setting heap size, printing GC details and viewing versions. Understanding JVM helps to better develop, debug and optimize Java programs.

Jun 27, 2025 am 12:45 AM

What is JDBC?

JDBC is the basic API for Java operating databases. Its core function is to provide a unified interface to simplify the connection and interaction of different databases. The core components of JDBC include DriverManager for loading drivers and establishing connections, Connection executes SQL statements on behalf of database sessions, Statement or PreparedStatement, and ResultSet stores query results. The basic steps to using JDBC are: 1. Load the database driver; 2. Establish a database connection; 3. Create a Statement object; 4. Execute SQL statements and process the results; 5. Close resources to avoid leakage. Different databases need to select corresponding drivers, such as MySQL uses m

Jun 27, 2025 am 12:43 AM

What are operators in Java?

Operators in Java are basic tools for manipulating data, mainly including arithmetic operators, comparison operators, assignment and compound assignment operators, and logical operators. 1. The arithmetic operators include addition, subtraction, multiplication, division and balance, such as , -, *, /, %, where the integer division result is still an integer; 2. The comparison operator returns a Boolean value, such as ==, !=, >, =,

Jun 27, 2025 am 12:37 AM

When to override equals and hashCode?

When a custom class needs to logically judge "equality" and be used for hash collections, equals() and hashCode() must be overridden at the same time. 1. When you need to judge equality based on the object content rather than reference, use the Set.contains() method or inheritance class to add fields that affect equality, 2. Rewriting equals() must rewrite hashCode() synchronously to ensure that equal objects return the same hash value and avoid abnormal behavior of hash collections; 3. When implementing correctly, consistent fields should be used, null and basic types should be processed, and mutable fields should be avoided; 4. Automatically generate code with Lombok or IDE to simplify operations.

Jun 27, 2025 am 12:31 AM

What is reflection in Java?

Java reflection allows checking and manipulating components such as classes, methods, fields at runtime, and supports dynamic creation of instances, calling methods, and accessing fields, especially for frameworks such as Spring and Hibernate. Its core functions include: 1. Check the class structure; 2. Dynamically create instances; 3. Access private or protected members; 4. Call methods under unknown types. Practical applications include dependency injection, ORM mapping, testing tools and serialization libraries. Examples of usage include loading classes, creating instances, getting and calling methods. Notes include performance overhead, security restrictions, code obfuscation issues and loss of compile-time checks. Therefore, reflection should be used with caution and is suitable for building a common framework rather than everyday business logic.

Jun 27, 2025 am 12:02 AM

Difference between overloading and overriding?

The core difference between Overloading and Overriding lies in the scope of action and the implementation mechanism. 1. Overloading occurs in the same class, with the same method names but different parameters, which are used to provide flexibility; 2. Overriding occurs between the subclass and the parent class, with the same method names and parameters, which are used to change existing behavior; 3. Overloading is bound at compile time, and Overriding is bound at runtime; 4. Overloading cannot be distinguished by return type only, while Overriding cannot change the limitation of access permissions; 5. Overriding cannot overwrite private, static or final methods. master

Jun 26, 2025 am 01:23 AM

Difference between inner and nested static classes?

ThedifferencebetweeninnerandnestedstaticclassesinJavaliesintheirrelationshipwiththeouterclassinstance.Anestedstaticclassisindependentoftheouterclassinstance,canaccessonlystaticmembersdirectly,andcanbeinstantiatedwithoutanouterobject.Aninnerclassrequi

Jun 26, 2025 am 01:23 AM

What is dependency injection concept?

Dependencyinjection(DI)isadesignpatternthatenablesloosecouplingbyallowingdependenciestobeprovidedexternally.Insteadofaclasscreatingitsowndependencies,theyarepassedin,makingcodemoreflexible,testable,andmaintainable.DIfacilitateseasyswappingofimplement

Jun 26, 2025 am 01:18 AM

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