Enums in Java are special classes that represent fixed number of constant values. 1. Use the enum keyword definition; 2. Each enum value is a public static final instance of the enum type; 3. It can include fields, constructors and methods to add behavior to each constant; 4. It can be used in switch statements, supports direct comparison, and provides built-in methods such as name(), ordinal(), values() and valueOf(); 5. Enumeration can improve the type safety, readability and flexibility of the code, and is suitable for limited collection scenarios such as status codes, colors or week.

The rational use of semantic tags in HTML can improve page structure clarity, accessibility and SEO effects. 1. Used for independent content blocks, such as blog posts or comments, it must be self-contained; 2. Used for classification related content, usually including titles, and is suitable for different modules of the page; 3. Used for auxiliary information related to the main content but not core, such as sidebar recommendations or author profiles. In actual development, labels should be combined and other, avoid excessive nesting, keep the structure simple, and verify the rationality of the structure through developer tools.

When the Windows search bar cannot enter text, common solutions are: 1. Restart the Explorer or computer, open the Task Manager to restart the "Windows Explorer" process, or restart the device directly; 2. Switch or uninstall the input method, try to use the English input method or Microsoft's own input method to eliminate third-party input method conflicts; 3. Run the system file check tool, execute the sfc/scannow command in the command prompt to repair the system files; 4. Reset or rebuild the search index, and rebuild it through the "Index Options" in the "Control Panel". Usually, we start with simple steps first, and most problems can be solved step by step.

There are three main differences between Callable and Runnable in Java. First, the callable method can return the result, suitable for tasks that need to return values, such as Callable; while the run() method of Runnable has no return value, suitable for tasks that do not need to return, such as logging. Second, Callable allows to throw checked exceptions to facilitate error transmission; while Runnable must handle exceptions internally. Third, Runnable can be directly passed to Thread or ExecutorService, while Callable can only be submitted to ExecutorService and returns the Future object to

TheVSCodeterminalnotworkingisoftenduetoafrozenterminal,misconfiguredshellsettings,conflictingextensionsorstartupscripts,oracorruptedcache/installation.1.FirstcheckiftheterminalisfrozenbytypingacommandlikelsordirandpressingEnter;ifunresponsive,closean

Java's class loading mechanism is implemented through ClassLoader, and its core workflow is divided into three stages: loading, linking and initialization. During the loading phase, ClassLoader dynamically reads the bytecode of the class and creates Class objects; links include verifying the correctness of the class, allocating memory to static variables, and parsing symbol references; initialization performs static code blocks and static variable assignments. Class loading adopts the parent delegation model, and prioritizes the parent class loader to find classes, and try Bootstrap, Extension, and ApplicationClassLoader in turn to ensure that the core class library is safe and avoids duplicate loading. Developers can customize ClassLoader, such as URLClassL

The key to Java exception handling is to distinguish between checked and unchecked exceptions and use try-catch, finally and logging reasonably. 1. Checked exceptions such as IOException need to be forced to handle, which is suitable for expected external problems; 2. Unchecked exceptions such as NullPointerException are usually caused by program logic errors and are runtime errors; 3. When catching exceptions, they should be specific and clear to avoid general capture of Exception; 4. It is recommended to use try-with-resources to automatically close resources to reduce manual cleaning of code; 5. In exception handling, detailed information should be recorded in combination with log frameworks to facilitate later

Polymorphism is one of the core features of Java object-oriented programming. Its core lies in "one interface, multiple implementations". It implements a unified interface to handle the behavior of different objects through inheritance, method rewriting and upward transformation. 1. Polymorphism allows the parent class to refer to subclass objects, and the corresponding methods are called according to the actual object during runtime; 2. The implementation needs to meet the three conditions of inheritance relationship, method rewriting and upward transformation; 3. It is often used to uniformly handle different subclass objects, collection storage and framework design; 4. When used, only the methods defined by the parent class can be called. New methods added to subclasses need to be transformed downward and accessed, and pay attention to type safety.