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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

What is a Map?

Amapisavisualtoolthatrepresentsgeographicareasandhelpspeopleunderstandspatialrelationshipsandnavigateeffectively.Itcomesinvarioustypes,includingtopographicmapsshowingelevation,politicalmapshighlightingborders,thematicmapsdisplayingspecificdatalikecli

Jun 30, 2025 am 01:22 AM

How to use `LocalTime`?

LocalTime instances can be created by obtaining the current time, specifying the specific time, or parsing the string, such as LocalTime.now(), LocalTime.of(14,30) and LocalTime.parse("15:45"); the operation time needs to be generated by plusHours(), minusMinutes() or with() to achieve addition and subtraction or adjustment of specific parts; it is suitable for representing the time points of daily repetition, but does not contain date and time zone information. The isBefore() or isAfter() method should be used when comparing.

Jun 30, 2025 am 01:16 AM

Difference between `wait` `notify` and `notifyAll`?

Thedifferencebetweenwait(),notify(),andnotifyAll()liesinhowtheycoordinatethreads.1.wait()makesathreadreleasethelockandpauseuntilnotified.2.notify()wakesuponewaitingthread,chosenbytheJVM.3.notifyAll()wakesupallwaitingthreads,lettingthemcompeteforthelo

Jun 30, 2025 am 01:12 AM

What is a EAR file?

EAR files are packaging formats used in JavaEE to deploy enterprise-level applications. The structure includes 1. One or more WAR files (Web applications), 2. One or more JAR files (such as EJB modules, general libraries), 3. An application.xml deployment description file; the difference from WAR/JAR is that WAR is dedicated to web applications, and JAR is more general, while EAR is a higher-level packaging method that integrates multiple modules; it is commonly found in traditional enterprise systems, especially in application servers such as IBMWebSphere and OracleWebLogic. It is suitable for scenarios where multi-module centralized deployment, unified management services, and inter-module isolation and resource sharing.

Jun 30, 2025 am 01:10 AM

What is a ConcurrentHashMap?

ConcurrentHashMap is a thread-safe hash table implementation, suitable for efficient concurrent reading and writing in multi-threaded environments. 1. It improves concurrency performance through segmented lock (JDK1.7) or CAS synchronized (JDK1.8) mechanism, allowing multiple threads to operate different parts of data without blocking; 2. The usage method is the same as HashMap, and common operations such as put, get, remove, etc. are thread-safe; 3. Note that putIfAbsent and other methods should replace non-atomic judgments and insert operations to ensure thread safety; 4. No exceptions were thrown during traversal, but the results may be non-real-time, and are suitable for scenarios such as cache, counters and shared state management.

Jun 30, 2025 am 01:08 AM