How to use HashMap.get() method in Java to get the value in the map?

AdeadlockinJavaoccurswhentwoormorethreadsareblockedforever,eachwaitingforaresourceheldbytheother,typicallyduetocircularwaitcausedbyinconsistentlockordering;thiscanbepreventedbybreakingoneofthefournecessaryconditions—mutualexclusion,holdandwait,nopree

UseOptional.empty(),Optional.of(),andOptional.ofNullable()tocreateOptionalinstancesdependingonwhetherthevalueisabsent,non-null,orpossiblynull.2.CheckforvaluessafelyusingisPresent()orpreferablyifPresent()toavoiddirectnullchecks.3.Providedefaultswithor

The core of SpringDataJPA and Hibernate working together is: 1. JPA is the specification and Hibernate is the implementation, SpringDataJPA encapsulation simplifies DAO development; 2. Entity classes map database structures through @Entity, @Id, @Column, etc.; 3. Repository interface inherits JpaRepository to automatically implement CRUD and named query methods; 4. Complex queries use @Query annotation to support JPQL or native SQL; 5. In SpringBoot, integration is completed by adding starter dependencies and configuring data sources and JPA attributes; 6. Transactions are made by @Transactiona

Understand JCA core components such as MessageDigest, Cipher, KeyGenerator, SecureRandom, Signature, KeyStore, etc., which implement algorithms through the provider mechanism; 2. Use strong algorithms and parameters such as SHA-256/SHA-512, AES (256-bit key, GCM mode), RSA (2048-bit or above) and SecureRandom; 3. Avoid hard-coded keys, use KeyStore to manage keys, and generate keys through securely derived passwords such as PBKDF2; 4. Disable ECB mode, adopt authentication encryption modes such as GCM, use unique random IVs for each encryption, and clear sensitive ones in time

IfLeagueofLegendssettingsaren’tsaving,trythesesteps:1.Runthegameasadministrator.2.GrantfullfolderpermissionstotheLeagueofLegendsdirectory.3.Editandensuregame.cfgisn’tread-only.4.Disablecloudsyncforthegamefolder.5.RepairthegameviatheRiotClient.

The Pattern class is used to compile regular expressions, and the Matcher class is used to perform matching operations on strings. The combination of the two can realize text search, matching and replacement; first create a pattern object through Pattern.compile(), and then call its matcher() method to generate a Matcher instance. Then use matches() to judge the full string matching, find() to find subsequences, replaceAll() or replaceFirst() for replacement. If the regular contains a capture group, the nth group content can be obtained through group(n). In actual applications, you should avoid repeated compilation patterns, pay attention to special character escapes, and use the matching pattern flag as needed, and ultimately achieve efficient

Chrome bookmark editing is simple and practical. Users can enter the bookmark manager through the shortcut keys Ctrl Shift O (Windows) or Cmd Shift O (Mac), or enter through the browser menu; 1. When editing a single bookmark, right-click to select "Edit", modify the title or URL and click "Finish" to save; 2. When organizing bookmarks in batches, you can hold Ctrl (or Cmd) to multiple-choice bookmarks in the bookmark manager, right-click to select "Move to" or "Copy to" the target folder; 3. When exporting and importing bookmarks, click the "Solve" button to select "Export Bookmark" to save as HTML file, and then restore it through the "Import Bookmark" function if necessary.

IfJavaisnotrecognizedinCMD,ensureJavaisinstalled,settheJAVA_HOMEvariabletotheJDKpath,andaddtheJDK'sbinfoldertothesystemPATH.RestartCMDandrunjava-versiontoconfirm.