The Optional class is used to safely handle values ??that may be null, avoiding null pointer exceptions. 1. Create an instance using Optional.ofNullable to handle null values. 2. Check and access values ??through isPresent or ifPresent security to avoid direct call to get to cause exceptions. 3. Use orElse and orElseGet to provide default values, or use orElseThrow to throw a custom exception. 4. Convert or filter values ??through map and filter chain operations to improve code readability and robustness.

Use the getClass() method to get the runtime class of the object, such as str.getClass() to return the Class object; for types, you can directly use the String.class syntax. The Class class provides methods such as getName(), getSimpleName() to obtain class information, such as num.getClass().getSimpleName() to output Integer.

Atwo-dimensionalarrayinJavaisanarrayofarrays,declaredwithtwobrackets,likeint[][]matrix,andcanbeinitializedwithvaluesorusingnew;forexample,int[][]matrix={{1,2},{3,4}};createsa3x2matrix.

ThecurrentworkingdirectoryinJavacanbeobtainedusingSystem.getProperty("user.dir"),whichreturnstheabsolutepathwheretheprogramwaslaunched;alternatively,Paths.get("").toAbsolutePath().toString()fromtheNIOAPIprovidesthesameresult,witht

AsingletonclassinJavaensuresonlyoneinstanceexiststhroughoutanapplication’slifecyclebyusingaprivateconstructor,aprivatestaticinstance,andapublicstaticgetInstance()method;commonimplementationsincludeeagerinitialization,lazyinitialization,thread-safelaz

GenericsinJavaprovidecompile-timetypesafetyandeliminatetheneedforcastingbyallowingclasses,interfaces,andmethodstooperateontypeparameters;forexample,usingListensuresonlystringscanbeadded,preventingruntimeClassCastExceptions;genericsworkviatypeparamete

Caches and cookies can be cleaned for specific websites to resolve UC browser page loading exceptions. 1. Go to Settings → Privacy and Security → Website Data Management, search for the target website and clear its data; 2. Use the invisible browsing mode to access the problem website to avoid data retention; 3. Reset the storage by disabling and enabling website permissions, and force clear the old cache.

You can back up Wukong browser history by manually recording, extracting databases or automated scripts. First, you can enter the history page to copy or take photos and save them manually; secondly, if the device is rooted, you can access the /data/data/com.wukong.browser/databases/ path with the file manager, export the history.db database and parse it into CSV with the SQLite tool; finally, for rootless devices, you can use Auto.js and other tools to write scripts, call the accessibility service to automatically slide the historical page and take screenshots to archive, and realize semi-automated backup.