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How to check if a file exists in Java

UseFiles.exists(Paths.get(path))tocheckifafileexistsinJava,asitisthemodernandrecommendedapproachwithbetterhandlingofsymboliclinksandpermissions;2.Optionally,combinewithFiles.isRegularFile(),Files.isReadable(),orFiles.isWritable()toverifyfiletypeandac

Aug 07, 2025 pm 04:35 PM

java File existence

Writing High-Performance Java Code: Common Pitfalls to Avoid

Avoidunnecessaryobjectcreationandautoboxinginloops;2.UseStringBuilderwithpre-sizedcapacityforstringconcatenation;3.Chooseappropriatecollectionsandsetinitialcapacities;4.Minimizesynchronizationandpreferconcurrentcollections;5.Usestreamsjudiciouslyanda

Aug 07, 2025 pm 04:01 PM

How to perform a shallow copy of an object in Java?

To implement shallow copy in Java, you need to implement the Cloneable interface and rewrite the clone() method; 1. Implement the Cloneable interface to avoid CloneNotSupportedException; 2. Rewrite the clone() method and call super.clone() to create a shallow copy; the shallow copy only copies the object itself, and its reference fields still point to the original object, so modification of the mutable reference fields will affect the original object; when the object contains a basic type or immutable reference, a shallow copy should be used, if an independent copy is required, a deep copy should be used; the same effect can also be achieved through the copy constructor, such as Person(Personother){this.name=othe

Aug 07, 2025 pm 03:43 PM

java Shallow copy

What is the difference between an abstract class and an interface in Java?

Abstractclassescanhavebothabstractandconcretemethods,constructors,andinstancevariables,whileinterfacesbeforeJava8onlyallowedabstractmethods,butfromJava8 supportdefaultandstaticmethods.2.Aclasscanextendonlyoneabstractclassusing"extends",butc

Aug 07, 2025 pm 03:15 PM

Exploring the Java Module System (JPMS)

Java9 introduced the Java module system (JPMS), aiming to achieve strong packaging, reliable dependency management and scalability through modularity; 1. The module declares required modules (requires) and export packages (exports) through module-info.java; 2. Provides strong packaging, default internal packages are not visible; 3. Enables reliable configuration and checks dependencies at startup; 4. Supports the use of jlink to create a streamlined runtime; 5. Pay attention to automatic modules, unnamed modules and prohibited split package issues; 6. You can gradually migrate and combine --add-opens and other options to deal with reflection requirements; ultimately, JPMS improves architectural clarity, security and maintenance, which is an important foundation for building robust Java applications.

Aug 07, 2025 pm 02:51 PM

A Practical Look at the Java `switch` Expression

Java's switch expressions have become a standard feature since Java14, and can return values and have a simpler syntax than traditional switch statements. 1. Use the -> arrow syntax to avoid break and unexpected fall-through; 2. The compiler ensures that all possible values of enum and sealed types are processed to improve code security; 3. Use {} blocks to match yield to return values in complex logic. It is recommended to give priority to switch expressions in Java 14 and above. It not only reduces errors, but also makes the code clearer and more functional, suitable for value mapping, replaces long if-else chains and initialization variables. It is a substantial language upgrade rather than a simple syntactic sugar.

Aug 07, 2025 pm 02:43 PM

How to implement a singleton pattern in Java?

Eagerinitializationcreatestheinstanceatclassloadtime,ensuringthreadsafetybutwithoutlazyloading;useitwhentheinstanceisalwaysneededorinitializationisinexpensive.2.Double-checkedlockingenablesthread-safelazyloadingbyusingavolatilevariableandsynchronized

Aug 07, 2025 pm 02:27 PM

How to use the Java Platform Module System (JPMS)

Amoduleisdefinedusingamodule-info.javafilethatdeclaresthemodulename,requiredmodules,exportedpackages,andoptionalserviceusesorprovides,withrequiresspecifyingdependenciesandexportsmakingpackagesaccessible.2.Setupastandardprojectstructurewithmodule-info

Aug 07, 2025 pm 02:15 PM

JPMS Java模塊系統(tǒng)

Advanced Java Generics and Type Erasure Explained

Javagenericsprovidecompile-timetypesafetybutareerasedatruntimeduetotypeerasure.1.Typeerasureremovesgenerictypeinformationduringcompilation,replacingtypeparameterswithboundsorObjectandinsertingcasts.2.Wildcardslike?extendsTand?superTenableflexible,saf

Aug 07, 2025 pm 02:13 PM

java Generics

Advanced Java Debugging with Remote Debugging

Remote debugging is implemented by adding JVM parameters and configuring the IDE. Specific steps: 1. Add the -agentlib:jdwp parameter at startup to enable JDWP, configure transport, server, suspend and address parameters; 2. Create a new remote debugging configuration in IntelliJIDEA or Eclipse, fill in the IP and port for connection; 3. Pay attention to avoid long-term activation of debug mode, use suspend=y with caution, prevent port conflicts, and improve debugging efficiency with logs.

Aug 07, 2025 pm 01:39 PM

What are the common methods to iterate over a Map in Java?

traversal with entrySet() is the most common and efficient way to get keys and values; 2. Use keySet() to traverse only keys, if you need a value, you can get it through the get method, but there may be performance loss; 3. Use values() to traverse only values, which is suitable for scenarios without keys; 4. Use Iterator to safely delete elements during traversal, suitable for scenes that need to be controlled; 5. Use Java8 forEach() combined with Lambda expression syntax is concise and suitable for simple operations; in summary, when key-value pairs are needed, entrySet() is recommended, and functional style can be used forEach(). When elements need to be deleted, you should use Iterator. When only keys or values can be processed, keySet can be used respectively (

Aug 07, 2025 pm 01:29 PM

java map Map 迭代

How to check thread status in Java

UseThread.getState()togetthecurrentstateofathread,whichreturnsaThread.Stateenumvalue;2.ThepossiblestatesareNEW,RUNNABLE,BLOCKED,WAITING,TIMED_WAITING,andTERMINATED,eachrepresentingaspecificphaseinthethread'slifecycle;3.Youcanmonitorthestateinreal-tim

Aug 07, 2025 pm 01:05 PM

How to sort a Map by value in Java

To sort the values of the Map, you need to convert the entries into a list or stream and sort them using a comparator. The specific steps are: 1. Use entrySet() to obtain the entries collection; 2. Sort by value through List.sort() or Stream.sorted() and Map.Entry.comparingByValue(); 3. Optionally collect the LinkedHashMap with Collectors.toMap() to maintain the order; if descending order is required, use reversed(). When processing equal values, you can add thenComparing() key to sort quadratic order, and finally get a value-sorted and ordered Map.

Aug 07, 2025 pm 12:41 PM

java Map排序

How to implement a binary search in Java

BinarysearchrequiresasortedarrayandhasO(logn)timecomplexity.2.Theiterativeimplementationusesleftandrightpointerswithmid=left (right-left)/2topreventoverflowandreturnstheindexiffound,else-1.3.TherecursiveversionfollowsthesamelogicbutusesO(logn)stacksp

Aug 07, 2025 am 11:16 AM

java binary search