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Understanding Java Garbage Collection Processes

Java garbage collection (GC) is a mechanism by which JVM automatically manages memory, avoiding manual memory management by identifying and freeing objects that are no longer in use. 1. GC uses accessibility analysis to determine the survival of objects, with heap as the main recycling area; 2. Java heap is divided into the Cetacean and the Old Age. The Cetacean includes the Eden area and the two Survivor areas. Most objects are allocated in the Eden area. MinorGC cleans up the area and copies the surviving objects to the Survivor area. Long-term surviving objects enter the old age; 3. Mainstream GC algorithms include mark-clearing, copying (for the Cetacean), mark-tissue (for the elderly); 4. Commonly used collectors include SerialGC, ParallelScavenge, CMS,

Jul 07, 2025 am 01:07 AM

Tools and Techniques for Profiling Java Application Performance

Java application performance tuning should rely on tools and data rather than guesswork. 1. Use JVM's own tools such as jstat to analyze GC, jstack to troubleshoot thread problems, and jmap and MAT analyze memory leaks; 2. Visual tools such as JProfiler, YourKit, and VisualVM can intuitively view the time-consuming of calling links and methods; 3. APM tools such as SkyWalking, Pinpoint, and NewRelic support full-link monitoring and distributed tracking; 4. Combining logs and Prometheus Grafana to achieve indicator monitoring and trend warning. Choosing tools rationally and understanding the results is key.

Jul 07, 2025 am 01:05 AM

Utilizing Java Generics for Enhanced Type Safety

Javagenericsareapowerfulfeaturethatallowsyoutowriteflexible,reusablecodewithoutsacrificingtypesafety.Insteadofwritingseparateclassesormethodsfordifferentdatatypes,youcancreategenericonesthatworkwithanytype—whilestill

Jul 07, 2025 am 12:56 AM

Using Java Future for Asynchronous Operations

Java's Future interface executes and obtains results through asynchronous tasks. Common methods include: 1. Submit a task to obtain a Future instance; 2. Call get() to block the result or set a timeout to avoid blocking; 3. Cancel the task through cancel() and use isCancelled() to judge the status; 4. Capture the ExecutionException to handle exceptions; 5. Manually coordinate the results of multiple Future merging, but does not support chain operations.

Jul 07, 2025 am 12:33 AM

What is the difference between Heap and Stack memory in Java?

In Java, heap and stack memory have different functions: the heap is used to store objects, and the stack is used to store method calls and local variables. 1. The heap is a dynamically allocated memory pool, managed by the garbage collector, and stores objects created through new; 2. The stack adopts a strict LIFO model, storing local variables and method parameters when method calls, and is automatically cleared after the method is executed; 3. The heap memory is flexible but slow, and the life cycle is controlled by GC, while the stack memory is fast but the capacity is limited, and the life cycle is consistent with the method execution period; common problems include the heap memory leak and the stack overflow error.

Jul 07, 2025 am 12:23 AM

Using the new Java Date and Time API (java.time).

Java8's java.time package provides thread-safe and clear design date and time processing methods. Get the current date and time available LocalDateTime.now() or ZonedDateTime.now(ZoneId.of("Asia/Shanghai")); 1. Use DateTimeFormatter to format, such as ISO_DATE or custom format; 2. The parsing needs to ensure that the string and the format are strictly matched; 3. Addition and subtraction operations are implemented through plusXxx()/minusXxx(); 4. Use isBefore()/isAfter() for comparison; 5. Use time zone conversion

Jul 06, 2025 am 02:55 AM

java time api

How Java ClassLoaders Work Internally

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

Jul 06, 2025 am 02:53 AM

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When to Use the 'static' Keyword in Java Classes

In Java, the static keyword is used to associate variables, methods, or nested classes with the class itself rather than instances. 1. When a class-level variable is needed, such as a shared counter, use static variables; 2. When the method does not depend on the instance state, such as a tool method, use static methods; 3. When a nested class does not need to access the instance variables of an external class, use static nested classes; 4. When an initialization task needs to be executed when the class is loaded, use static code blocks. These usages help save memory and avoid unnecessary object creation, but use mutable static variables with caution to avoid difficult-to-trace errors.

Jul 06, 2025 am 02:53 AM

What is the lifecycle of a thread?

The thread life cycle contains five clear states: 1. New state: The thread is created but has not started yet, and does not consume CPU resources; 2. Runnable state: The thread has been started and waited or is executing, which is determined by the scheduler; 3. Blocked/Waiting/TimedWaiting: The thread does not execute due to locking, infinite waiting or timeout waiting, but it still survives; 4. Terminated state: The thread enters this state after completing the task or exits abnormally and cannot be restarted; 5. During the entire life cycle, the thread states are converted in sequence. Understanding these states helps to avoid deadlocks and resource competition issues.

Jul 06, 2025 am 02:50 AM

Building Network Applications with Java Sockets

Java's Socket programming is suitable for building network applications based on TCP or UDP. 1. ServerSocket and Socket are used for TCP to ensure reliable connections; 2. DatagramSocket is used for UDP, suitable for scenarios with high real-time requirements. When writing a TCP application, the server listens and accepts connections through ServerSocket, and the client actively connects through Socket. To handle multiple clients, concurrent connections can be managed using threads or thread pools. Notes include avoiding port conflicts, handling exceptions, closing resources and setting timeouts to ensure program stability and efficiency.

Jul 06, 2025 am 02:46 AM

How to use the Java Stream API?

When using the JavaStreamAPI to process collection data, there are a number of ways to create streams and perform operations. Common steps include: 1. Create a stream from a collection, array or directly generate elements; 2. Use intermediate operations such as filter, map, sorted to build a processing flow; 3. Trigger actual execution through termination operations such as collect, forEach, reduce, etc.; 4. Parallel flow can be enabled in large data scenarios to improve performance, but pay attention to thread safety and task overhead to avoid improper use affecting efficiency.

Jul 06, 2025 am 02:45 AM

How to handle exceptions properly in Java?

The key to handling exceptions in Java is to catch them, handle them clearly, and not cover up problems. First, we must catch specific exception types as needed, avoid general catches, and prioritize checkedexceptions. Runtime exceptions should be judged in advance; second, we must use the log framework to record exceptions, and retry, rollback or throw based on the type; third, we must use the finally block to release resources, and recommend try-with-resources; fourth, we must reasonably define custom exceptions, inherit RuntimeException or Exception, and carry context information for easy debugging.

Jul 06, 2025 am 02:43 AM

java Exception handling

Security Concerns When Using Java Reflection

The Java reflection mechanism has three major security risks: 1. Break through access control restrictions, read or modify private fields, it is recommended to avoid using reflection on sensitive classes and enable security managers; 2. Abuse of reflection to create instances or execute dangerous methods, which may lead to malicious code execution, whitelist verification and use a sandbox environment; 3. The class loading process may introduce malicious classes, and it is necessary to control the source of the class loader and verify the integrity of the dynamically loaded classes. Reasonable restrictions and reviews can reduce security risks.

Jul 06, 2025 am 02:42 AM

How to execute a query in JDBC?

Key steps in executing JDBC queries include: loading the driver and establishing a connection, creating a Statement and executing a query, processing a result set, and closing resources. First, the database driver must be loaded and a connection must be established. For example, when using MySQL, the driver is loaded through Class.forName() and the connection is obtained with DriverManager; then create a Statement through conn.createStatement() and call executeQuery() to execute SELECT query; then iterate over the ResultSet to extract the field value, note that the field name must match the database column name; finally, be sure to close the ResultSet, Statement and Co

Jul 06, 2025 am 02:41 AM