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What is Javadoc?

Javadoc is a tool in Java for generating API documents, describing code elements through/annotations and tags such as @param and @return. Using javadoc commands or IDEs can quickly generate HTML documents, which helps team collaboration and improves code maintainability and professionalism. 1. Comments start with / and use tags to describe parameters, return values, etc.; 2. Use javadoc command or IDE to generate documents; 3. Mainly used for interface description, improve development efficiency, and publish as part of the SDK.

Jul 01, 2025 am 12:44 AM

javadoc Document generation

What is a `Statement` object?

AStatementobjectinJavaisusedtoexecuteSQLqueriesandcommandswithadatabaseviaJDBC.1.ItallowsexecutionofSELECT,INSERT,UPDATE,DELETE,andDDLstatements.2.ItiscreatedusingthecreateStatement()methodofaConnectionobject.3.ResultSethandlesqueryresultsbyiterating

Jul 01, 2025 am 12:37 AM

jdbc

What is the `import static` statement?

importstaticinJavaallowsaccessingstaticmemberswithoutclassqualification.1.ItsimplifiescodereadabilitywhenusingconstantslikeMathUtils.PIbecomingPI.2.Itappliestoutilitymethods,suchaslog(),reducingverbosity.3.SelectiveimportsusingasListinsteadof*prevent

Jul 01, 2025 am 12:14 AM

java

How to prevent deadlock?

The key to preventing deadlocks is to understand the cause of it and adopt reasonable strategies, which mainly includes four points: 1. Understand the four necessary conditions for deadlocks (mutex, holding and waiting, not preemptive, and loop waiting). Breaking one of them can prevent deadlocks; 2. Avoid loop waiting. The common practice is to unify the order of resource requests, such as all threads apply for resources in order A→B; 3. Set a timeout mechanism or use tryLock() and try to obtain resources to avoid unlimited waiting; 4. Use tools such as jstack, VisualVM, etc. to detect and monitor potential deadlocks, and combine stress testing and log analysis to find problems in advance.

Jul 01, 2025 am 12:11 AM

How to handle null with Optional?

Use Optional to avoid abuse and is suitable for return values ??rather than intermediate variable processing. 1. Do not use Optional for local variable judgment, such as userOpt.isPresent(), which increases overhead; 2. It is recommended to use it as a method return type to clearly express the "possibly resultless" semantics, such as findUserById returns Optional; 3. Use map and filter to simplify object chain calls, such as using chain map to avoid NullPointerException when obtaining user.getAddress().getCity(), and use orElse to provide default values; 4. Avoid wrapping basic types or collection classes because they

Jun 30, 2025 am 01:35 AM

How to use the Streams API?

StreamsAPI is a functional programming tool introduced by Java 8, suitable for efficient processing of large amounts of data and simplifying code logic. It processes elements step by step in the form of a stream, and the core operations include intermediate operations (such as filter, map) and terminal operations (such as collect, forEach). Common ways to create Streams are obtained from collections, arrays, static methods, or generator functions. Applicable scenarios include tasks that require chain processing, functional style or parallel computing, and are not recommended for simple loops, small amounts of data, or when teams are not familiar with functional programming.

Jun 30, 2025 am 01:34 AM

What is a nested static class?

Anestedstaticclassisusedtologicallygrouphelperclasseswiththeouterclasswithoutneedinganinstanceoftheouterclass.1.Itorganizescodebykeepingrelatedclassestogether.2.Itallowsaccesstoprivatemembersoftheouterclass.3.Itavoidspollutingtheglobalnamespace.4.Iti

Jun 30, 2025 am 01:32 AM

How to convert wrapper object to primitive?

In Java, the methods of converting wrapper types to basic types mainly include automatic unboxing and manual unboxing. First, when using automatic unboxing, you can directly assign the wrapper class object to the basic type variable (such as intprimitive=wrapper;), but you need to note that if the object is null, a NullPointerException will be thrown; Second, you can manually call the corresponding unboxing method (such as wrapper.doubleValue()) to improve logical clarity and flexibly process the default value. Two key issues to be noted are: 1. Avoid unboxing the null value, and 2. Ensure that the type matches to prevent accuracy loss or data errors.

Jun 30, 2025 am 01:32 AM

What is the `volatile` keyword?

The volatile keyword is used to declare variables that may be modified outside the normal execution flow of the program, ensuring that memory is read and written directly every time you access it. 1. It prevents the compiler from optimizing access to the variable, such as cached into registers or instruction reordering; 2. It is often used in hardware registers, multi-threaded shared memory, signal processing functions and polling loops in embedded systems; 3. volatile does not guarantee thread safety and cannot replace synchronization mechanisms such as mutex locks; 4. Unlike const, const ensures that variables cannot be modified, and volatile means that the value of the variable may change unexpectedly; 5. The two can be used in combination, such as declaring read-only hardware registers.

Jun 30, 2025 am 01:31 AM

Keywords volatile

What are primitive data types?

Primitive data types are the most basic data building unit in programming, including integers, floating point numbers, characters, boolean values, and strings. They are directly supported by programming languages ??to define the types of data that variables can store. Using the correct primitive type can improve program performance and logical clarity and avoid memory waste or overflow problems. Reasonable declaration of variable types, avoiding the misuse of types, paying attention to the limitation of numerical ranges and clear naming are the four keys to effectively use original data types.

Jun 30, 2025 am 01:28 AM

What is the open closed principle?

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Jun 30, 2025 am 01:27 AM

When to use switch instead of if-else?

Suitable for using switch: First, multiple fixed value judgments, such as performing different logics according to the user operation type, the code is more intuitive and tidy at this time; second, performance-sensitive scenarios, because switches are usually compiled into jump tables, which are slightly more efficient; Notes: break must be added after each case to avoid unexpected fall-through. If fall-through is needed, comments should be added; unsuitable scenarios: range judgment or complex conditions such as Boolean expressions and multivariate combination judgments, if-else should be used.

Jun 30, 2025 am 01:26 AM

Difference between `throw` and `throws`?

InJava,throwisusedtomanuallytriggeranexceptionwithinamethod,whilethrowsdeclaresexceptionsamethodmightpropagate.1.throwisusedinsideamethodbodytoexplicitlythrowasingleexception,stoppingfurtherexecutionuntilcaught.2.throwsappearsinthemethodsignaturetoli

Jun 30, 2025 am 01:24 AM

What is abstraction?

Abstraction is a way of thinking that simplifies complex things. It helps us understand and deal with problems by ignoring details and grasping core features. For example, "mobile phone" represents a type of equipment that can make phone calls, send messages, and surf the Internet, rather than a specific brand or model; the "fruit" classification in supermarkets covers apples, bananas, etc., reflecting the process of ignoring individual differences and extracting common points; when defining "cars" in programming, only key attributes such as color, brand, and speed are retained; pattern helps manage complex systems, such as driving, only mastering the throttle brake logic without understanding the principles of the engine; during the learning process, abstract ability is reflected in identifying the commonalities of language structures and summarizing the rules of English grammar; practicing abstraction can start from small things such as organizing items and summarizing commonalities, and gradually improve the refining of simple structures from complexity;

Jun 30, 2025 am 01:22 AM