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What is JUnit?

JUnit is a testing framework mainly used in Java applications, and its core role is to support automated unit testing. Reasons for using JUnit include: 1. Supports automated testing to facilitate discovering regression problems caused by code changes; 2. Simple writing and define testing methods through @Test annotation; 3. Good integration with mainstream IDEs and build tools; 4. Have extensive community support. JUnit's key components include @Test, assertion methods (such as assertEquals), and annotations for pre- and post-test execution (such as @BeforeEach and @BeforeAll). It is suitable for unit testing scenarios, such as in TDD development, in continuous integration processes, or in regression testing.

Jun 28, 2025 am 01:16 AM

When does the `finally` block execute?

Finally blocks will be executed in programming regardless of whether an exception is thrown or not. The main function is to ensure that the cleanup code has a chance to run. 1. The finally block will run after the execution of the try and catch blocks. It will be executed even if an exception occurs and is processed, no exception occurs, or is returned from the try/catch. 2. If there is a return statement in a try or catch, finally will still be executed before the method actually returns, but the return in it may overwrite the original return value and should be avoided. 3. The most common use is resource cleaning, such as closing files, database connections, etc. to prevent resource leakage. 4. Before Java7, you need to manually write try-catch-finally for resource management.

Jun 28, 2025 am 01:05 AM

Why do we need wrapper classes?

Java uses wrapper classes because basic data types cannot directly participate in object-oriented operations, and object forms are often required in actual needs; 1. Collection classes can only store objects, such as Lists use automatic boxing to store numerical values; 2. Generics do not support basic types, and packaging classes must be used as type parameters; 3. Packaging classes can represent null values ??to distinguish unset or missing data; 4. Packaging classes provide practical methods such as string conversion to facilitate data parsing and processing, so in scenarios where these characteristics are needed, packaging classes are indispensable.

Jun 28, 2025 am 01:01 AM

Can a class have multiple main methods?

Yes,aclasscanhavemultiplemainmethodsthroughmethodoverloading,butonlyonewiththeexactsignaturepublicstaticvoidmain(String[]args)servesastheentrypoint.Otheroverloadedversionslikemain(Stringargs)ormain(int[]args)aretreatedasregularstaticmethodsandmustbec

Jun 28, 2025 am 12:58 AM

What is the exception hierarchy?

Exception hierarchy refers to the exception type organized in a tree structure in programming, and its core is the base class such as Python's Exception or Java's Throwable. 1. The exception hierarchy starts with BaseException, Exception, etc., and derives more specific exceptions such as IOException or NullPointerException. 2. Through the hierarchy, developers can accurately catch specific exceptions, such as first catching ValueError and then handling general exceptions. 3. When customizing exceptions, you should inherit the appropriate base class. For example, creating AppError as the basis for custom errors, and further refine DatabaseError.

Jun 28, 2025 am 12:55 AM

How to handle stack overflow errors?

Stack overflow errors are usually caused by recursion without termination or excessive local variables. When checking, you should first check whether the recursion logic is correct, ensure that there are clear termination conditions and gradually approach the termination point, and use loops when necessary; secondly, consider adjusting the thread stack size, but be careful to avoid wasting resources; finally, avoid excessively large local variables in the function and use dynamic allocation instead. 1. The main reason for stack overflow is infinite recursion or local variables occupy too much stack space. 2. Repair recursive logic requires termination judgment, such as adding n to factorial function

Jun 28, 2025 am 12:47 AM

What is the strictfp keyword?

The strictfp keyword is used to ensure that floating point operations in Java produce the same results on all platforms, which achieve consistency by forcing compliance with the IEEE754 standard. 1. It limits the accuracy of intermediate floating point results to float or double type to avoid slight errors caused by hardware differences; 2. It can be applied to class or method levels, but not to variables or constructors; 3. It is suitable for financial, scientific computing and other scenarios that require cross-platform consistency, which may slightly affect performance. This keyword is usually not required if precise control of floating point behavior is not required.

Jun 28, 2025 am 12:45 AM

java strictfp

What are bitwise operators?

Bitwiseoperatorsmanipulateindividualbitsofbinarynumbers.TheyperformoperationslikeAND(&),OR(|),XOR(^),NOT(~),leftshift(),enablingprecisecontroloverspecificbitswithoutaffectingothers.Theseoperatorsareusedinrealcodetoefficientlymanagesettings,flags,

Jun 28, 2025 am 12:26 AM

What is a package in Java?

PackagesinJavaorganizecodeintounitstopreventnamingconflictsandimproveorganization.1.Packagesgrouprelatedclasses,interfaces,andsub-packages.2.Theyavoidnameclashesbyallowingsame-namedclassesindifferentpackages.3.Theycontrolaccessusingpackage-privatevis

Jun 28, 2025 am 12:16 AM

How to use Gradle build tool?

The key to building a project with Gradle is to understand its structure and commands. After creating the project manually or with the IDE, the core files build.gradle and settings.gradle configure dependencies and subprojects respectively. Gradle construction is divided into three stages: initialization, configuration, and execution. Common tasks such as build and test can be viewed and run through gradletasks. Custom tasks can be defined in build.gradle, such as taskhello output text. Adding dependencies is completed in dependencies block, plugins such as java and application are introduced through plugins blocks, and improving functions such as running Java programs directly. Recommended

Jun 28, 2025 am 12:14 AM

What is the native keyword?

Nativekeyword refers to the keyword system natively supported by the platform, which is commonly found in ASO and advertising. It directly affects exposure and ranking, can be optimized without third-party tools, and is recognized by the platform first. Specific usage methods include: 1. GooglePlay crawls keywords through titles, subtitles, and descriptions; 2. AppStore provides 100-character keyword fields, separated by commas; 3. Advertising platforms such as Facebook and TikTok fill in keyword tags to match users. Optimization methods include basic research, avoiding stacking, regular inspection of the results, and combining competitive product analysis.

Jun 27, 2025 am 01:50 AM

What is the `finally` block?

Finally blocks are used to execute critical code that must be run regardless of whether an exception occurs, and are often used to clean up resources. Its core functions include: 1. Ensure that resources such as file, database connection are closed; 2. Ensure execution in different scenarios (such as exception thrown, early return); 3. Avoid resource leakage and improve program reliability. For example, after reading a file in Java, use finally to close the stream, even if there is a return statement in the try or catch, finally executes before it returns. When using it, please note: do not use return/break/continue in finally to avoid covering up exceptions; some languages ??such as Python recommend using with statements instead of final

Jun 27, 2025 am 01:49 AM

How does Java work?

The running mechanism of Java programs mainly includes compilation into bytecode, JVM execution and automatic memory management. First of all, Java code is compiled into platform-independent bytecode (.class file) through javac, realizing "write once, run everywhere". Next, the JVM loads the bytecode and interprets it by the execution engine or compiles it into machine code through JIT. At the same time, the JVM is also responsible for class loading, memory management and garbage collection. Then, the class loader (ClassLoader) loads class files from disk or network, and the runtime data area includes heap, stack, method area, etc. for data storage for program operation. Finally, the garbage collection mechanism automatically recognizes and frees object memory that is no longer in use, avoiding the complexity of manual memory management. The whole process starts

Jun 27, 2025 am 01:43 AM

What is a local inner class?

AlocalinnerclassinJavaisahelperclassdefinedwithinablockofcode,typicallyamethod,andisusefulforencapsulatinglogicthat'sonlyrelevantinthatspecificcontext.Itcanaccessouterclassmembersandfinaloreffectivelyfinallocalvariablesbutcannothaveaccessmodifiersors

Jun 27, 2025 am 01:41 AM