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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

java

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

Working with Files and I/O Streams in Java

The key to handling file and I/O streams in Java is to understand the basic concepts of streams and choose the right class library. 1. When reading text files, small files can be quickly loaded with Files.readAllLines(). It is recommended to use BufferedReader to read line by line to reduce memory usage. Pay attention to using try-with-resources to close streams and Paths.get() to build cross-platform paths. 2. It is recommended to use BufferedWriter to improve efficiency when writing files. Passing true when constructing FileWriter can achieve content addition. 3. You can use Files.copy() and Files.move() to copy or move files.

Jul 06, 2025 am 02:40 AM

java fileio

Introduction to the Java Module System (JPMS)

Java9 introduces module system (JPMS) to improve the code organization and dependency management of large-scale projects. The module declares the export package and dependencies through the module-info.java file. The core concepts include exports (exposed packages), requirements (declare dependencies), and opens (allow reflective access). Its advantages are reflected in stronger encapsulation, clearer dependency management and faster startup speed. The steps to use include creating module-info.java, explicit export and dependencies, and running the program with --module-path. Notes include module names that are unique, non-reliable, and support for gradual migration. Mastering the module system can help improve project maintainability and stability.

Jul 06, 2025 am 02:36 AM

Implementing `equals` and `hashCode` correctly in Java.

Youmustoverridebothequals()andhashCode()tomaintainconsistencyinhash-basedcollections.1)Overridingequals()withouthashCode()breaksthecontractthatequalobjectsmusthaveequalhashcodes,leadingtopotentiallookupfailuresinHashMaporHashSet.2)Implementequals()by

Jul 06, 2025 am 02:32 AM

java

Understanding the Java JIT Compiler's Functionality

The JIT compiler improves Java program performance by dynamically compiling hot code. The process includes: 1. Trigger compilation when the method is frequently called to reach the threshold; 2. Compile the bytecode into machine code; 3. Cache compiled code for reuse. The main influencing factors are: method call frequency, loop body code, JVM parameter settings and code complexity. Observing JIT behavior can be achieved through -XX: PrintCompilation parameters, JMH tools and performance analysis tools. Understanding JIT mechanisms can help optimize critical code paths and improve application performance.

Jul 06, 2025 am 02:21 AM

translater Java JIT