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

Java supports asynchronous programming including the use of CompletableFuture, responsive streams (such as ProjectReactor), and virtual threads in Java19. 1.CompletableFuture improves code readability and maintenance through chain calls, and supports task orchestration and exception handling; 2. ProjectReactor provides Mono and Flux types to implement responsive programming, with backpressure mechanism and rich operators; 3. Virtual threads reduce concurrency costs, are suitable for I/O-intensive tasks, and are lighter and easier to expand than traditional platform threads. Each method has applicable scenarios, and appropriate tools should be selected according to your needs and mixed models should be avoided to maintain simplicity

In Java, enums are suitable for representing fixed constant sets. Best practices include: 1. Use enum to represent fixed state or options to improve type safety and readability; 2. Add properties and methods to enums to enhance flexibility, such as defining fields, constructors, helper methods, etc.; 3. Use EnumMap and EnumSet to improve performance and type safety because they are more efficient based on arrays; 4. Avoid abuse of enums, such as dynamic values, frequent changes or complex logic scenarios, which should be replaced by other methods. Correct use of enum can improve code quality and reduce errors, but you need to pay attention to its applicable boundaries.

JavaNIO is a new IOAPI introduced by Java 1.4. 1) is aimed at buffers and channels, 2) contains Buffer, Channel and Selector core components, 3) supports non-blocking mode, and 4) handles concurrent connections more efficiently than traditional IO. Its advantages are reflected in: 1) Non-blocking IO reduces thread overhead, 2) Buffer improves data transmission efficiency, 3) Selector realizes multiplexing, and 4) Memory mapping speeds up file reading and writing. Note when using: 1) The flip/clear operation of the Buffer is easy to be confused, 2) Incomplete data needs to be processed manually without blocking, 3) Selector registration must be canceled in time, 4) NIO is not suitable for all scenarios.

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

Javaprovidesmultiplesynchronizationtoolsforthreadsafety.1.synchronizedblocksensuremutualexclusionbylockingmethodsorspecificcodesections.2.ReentrantLockoffersadvancedcontrol,includingtryLockandfairnesspolicies.3.Conditionvariablesallowthreadstowaitfor

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

HashMap implements key-value pair storage through hash tables in Java, and its core lies in quickly positioning data locations. 1. First use the hashCode() method of the key to generate a hash value and convert it into an array index through bit operations; 2. Different objects may generate the same hash value, resulting in conflicts. At this time, the node is mounted in the form of a linked list. After JDK8, the linked list is too long (default length 8) and it will be converted to a red and black tree to improve efficiency; 3. When using a custom class as a key, the equals() and hashCode() methods must be rewritten; 4. HashMap dynamically expands capacity. When the number of elements exceeds the capacity and multiplies by the load factor (default 0.75), expand and rehash; 5. HashMap is not thread-safe, and Concu should be used in multithreaded