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How to prevent deadlocks in Java concurrency?

The key to avoiding deadlocks is to understand the conditions for their occurrence and adopt appropriate strategies to avoid evasion, which includes the following 4 methods: 1. Unify the locking order to ensure that all threads acquire locks in the same order, thereby avoiding loop waiting; 2. Use explicit lock ReentrantLock and set the timeout time, try to acquire locks through the tryLock() method to avoid indefinite waiting; 3. Reduce the granularity and scope of use of the lock, only lock the key parts, try to use local variables and concurrent collection classes to reduce the probability of conflict; 4. Use tools such as jstack, VisualVM, etc. to detect potential deadlocks, and promptly identify and solve thread blocking problems.

Jul 08, 2025 am 02:54 AM

deadlock java concurrency

How Annotation Processing Works in Java

Annotation processor is an extended mechanism in the Java compilation stage, used to scan and process annotations in the source code, and can generate new code or preprocess it. Its core functions include: 1. When defining annotations, it needs to specify the retention policy and target element type; 2. Implement the AbstractProcessor class and rewrite key methods such as getSupportedAnnotationTypes, getSupportedSourceVersion and process; 3. Register the processor to declare a fully qualified name through a configuration file in the META-INF/services directory. Annotation processors are widely used in frameworks such as Dagger, ButterKnife and Roo

Jul 08, 2025 am 02:50 AM

java

Using Predicates and Consumers in Java 8 Functional Programming

In Java8, Predicate is used for conditional judgment, accepting parameters and returning boolean values, which are often used to filter data, such as filtering elements that meet the conditions in combination with filter() method; it can encapsulate complex logic and support combination operations of and(), or(), and negate(). Consumer is used to perform operations without return values. It is commonly used when forEach traversing the collection, such as printing or logging; it supports multiple operations in sequence through andThen() chain call. It should avoid too many side effects when using it. It is recommended to use references to improve the simplicity of the code and combine it with StreamAPI to play a greater role.

Jul 08, 2025 am 02:49 AM

How to perform Unit Testing in Java with JUnit?

Unit testing is crucial in Java projects, and mastering the key steps of the JUnit framework can help you get started quickly. 1. Introduce JUnit dependencies, use Maven or Gradle to add JUnitJupiter's API and Engine dependencies; 2. Write test classes, use @Test annotation to mark the test methods, and simplify assertion calls through static import; 3. Use @BeforeEach, @AfterEach, @BeforeAll and @AfterAll to manage the test life cycle; 4. Use assertEquals, assertTrue, assertNull and assertThrows to verify normal and exception logic.

Jul 08, 2025 am 02:48 AM

unit test junit

Explain the difference between `try-with-resources` and standard try-catch-finally in Java.

Themaindifferencebetweentry-with-resourcesandtry-catch-finallyinJavaisthattry-with-resourcesautomaticallyclosesresources,whiletry-catch-finallyrequiresmanualclosure.1.Try-with-resources,introducedinJava7,automaticallyclosesAutoCloseableresourcesafter

Jul 08, 2025 am 02:46 AM

Mastering Java Streams API for Data Processing

To master JavaStreams API, you need to understand the stream structure, avoid reusing streams, make good use of collect and groupingBy, and balance performance and readability. First, stream operations are divided into three parts: creation, intermediate operations, and terminal operations; second, streams can only be used once, and reused use will cause errors; second, collect and groupingBy can simplify aggregation statistics; finally, use Stream moderately to take into account performance and code clarity.

Jul 08, 2025 am 02:44 AM

java data processing

Understanding the Java Security Manager

JavaSecurityManager is a security component in the JVM that controls the permissions of the code. It defines the mapping between code source and permissions through the Policy file, checks sensitive operations at runtime, and throws a SecurityException if there is no authorization. Enabled to specify the policy file by adding the -Djava.security.manager and -Djava.security.policy parameters at startup. Use grant in Policy files to define codeBase and its permissions. Common permissions include FilePermission, SocketPermission, RuntimePermi

Jul 08, 2025 am 02:43 AM

What are Sealed Classes in Java?

Sealed classes are a feature introduced by Java 17 to limit which classes or interfaces can inherit or implement it. Its core role is to enhance control over inheritance by explicitly declaring allowed subclasses. Specifically: 1. Solve the problem that subclasses were not restricted at the language level before; 2. Support pattern matching (especially when combined with record classes); 3. Use sealed keywords and permits clauses to define allowed subclasses; 4. Subclasses must be declared final, sealed or non-sealed; 5. Applicable to closed type hierarchy, compile-time inspection and domain model design; 6. It is necessary to note that subclasses must be explicitly inherited in the same module or package. Sealing classes are suitable for scenarios that require strict inheritance control, but should not be abused.

Jul 08, 2025 am 02:42 AM

java

Connecting to Databases Using Java JDBC

The key to connecting to a database with JavaJDBC is the driver, URL format and connection method. First, you need to introduce the corresponding database JDBC driver, such as MySQL uses mysql-connector-java, PostgreSQL uses postgresql.jar, Oracle uses ojdbc8.jar, and ensure that the version matches the database; second, you need to correctly configure the connection information, such as the URL format of MySQL is jdbc:mysql://hostname:port/database name? Parameter 1=value 1&parameter 2=value 2. Common problems include the time zone not set, SSL not closed, host name or port error; finally, pay attention to exception handling and resource release, use tr

Jul 08, 2025 am 02:41 AM

Database Connectivity

How to handle transactions in JDBC?

There are five steps to handle JDBC transactions: 1. Turn off automatic submission to start manual transactions; 2. Execute multiple database operations; 3. Submit transactions in normal times; 4 Rollback in abnormal times; 5. Use save points to control the intermediate state when necessary. By default, JDBC is in auto-commit mode and submits each SQL statement after execution. When multiple operations are involved in actual development, connect.setAutoCommit (false) should be called to turn off automatic submission so that all operations are in the same transaction. The subsequent operations can be submitted through connection.commit() or rollback back to ensure data consistency. It is recommended to place the key code at t

Jul 08, 2025 am 02:40 AM

affairs jdbc

Deep Dive into the Java Virtual Machine Architecture

JVM is the core of Java program operation, including runtime data area, class loading mechanism, bytecode execution engine and garbage collection mechanism. 1. The runtime data area includes method area (metaspace after JDK8), heap (used to store object instances and perform garbage collection), stack (save thread method call information), local method stack (supports Native methods) and program counter (records the current instruction address). 2. The class loading mechanism consists of three ClassLoaders, Bootstrap, Extension and Application. It follows the parent delegation model and goes through five stages: loading, verification, preparation, parsing and initialization in turn to ensure the security and uniqueness of class loading. 3. Bytecode execution engine

Jul 08, 2025 am 02:38 AM

java virtual machine JVM architecture

Difference between `final`, `finally`, and `finalize` in Java.

In Java, final, finally and finalize are three keywords or methods that have different functions. 1. Final is used to restrict the modification or inheritance of variables, methods and classes to ensure immutability; 2. Finally used for code blocks in exception processing to ensure that resources release and other operations are always executed; 3. Finalize is an Object class method, which was used for cleaning before garbage collection, but has been deprecated. It is recommended to use AutoCloseable or try-with-resources instead. They are used to control invariance, ensure execution after exception handling, and replace resource cleaning methods.

Jul 08, 2025 am 02:30 AM

What is encapsulation?

EncapsulationinOOPisachievedbybundlingdataandmethodsintoasingleunitandcontrollingaccesstoanobject’sinternalstate.Itmattersbecauseithidesinternaldetails,allowsaccessonlythroughcontrolledmethods,andensuresdatavalidity.Toimplementit,fieldsaremadeprivate

Jul 08, 2025 am 02:29 AM

Implementing Producer-Consumer pattern using Java threads.

1. Using BlockingQueue is the most direct and recommended way to implement the Java producer-consumer model. It handles thread synchronization internally. The producer calls the put() method to block waiting queue space, and the consumer calls the take() method to block waiting data; 2. If the manual implementation requires the synchronized locking and wait/notify mechanism to coordinate thread behavior, the core is to loop check the conditions and operate the shared buffer within the synchronization block; 3. Notes include correct handling of interrupts, multi-threaded wake-up strategy to select notifyAll(), setting a reasonable buffer size, and elegantly closing threads.

Jul 08, 2025 am 02:28 AM

java thread Producer and Consumer