成年av网站18禁,av片在线观看

Article Tags

Home

Technical Articles

Java

Understanding Variable Scope and Lifetime in Java

The scope and life cycle of variables in Java depend on type. 1. The scope of local variables is limited to the code block, and the life cycle is destroyed as the code block ends; 2. The scope of member variables is the entire class, and the life cycle is created and destroyed with the object; 3. The scope of static variables is the entire class and can be accessed through the class name, and the life cycle exits from the class loading to the JVM; 4. The scope of parameter variables is limited to the method body, and the life cycle begins and ends with the method call. Variables should be kept as small as possible and short as possible to improve security.

Jul 05, 2025 am 02:36 AM

java variable scope

What is the purpose of the `static` keyword in Java?

Static keywords are used in Java to create variables and methods that belong to the class itself, rather than instances of the class. 1. Static variables are shared by instances of all classes and are suitable for storing data shared by all objects, such as schoolName in the Student class. 2. Static methods belong to classes and do not depend on objects. They are often used in tool functions, such as Math.sqrt(), and can only access other static members. 3. Static code blocks are used to perform initialization operations when class loading, such as loading libraries or setting logs. 4. Static inner classes can be instantiated independently of the external class, but non-static members of the external class cannot be accessed. Rational use of static can effectively manage class-level resources and behaviors.

Jul 05, 2025 am 02:36 AM

java static

Handling Common Java Exceptions Effectively

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

Jul 05, 2025 am 02:35 AM

java Exception handling

What is a `CallableStatement`?

CallableStatementinJavaisusedtocallstoredproceduresfromadatabase.1.Itenablesinteractionwithpre-writtenSQLcodeblocksstoredinthedatabasethatcanacceptparametersandreturnresults.2.Ithelpsreducenetworktraffic,improveperformance,andencapsulatebusinesslogic

Jul 05, 2025 am 02:35 AM

jdbc

Using the Java Streams API effectively.

Using JavaStreamAPI can improve code simplicity and parallelism, but the scenarios need to be selected reasonably. 1. Advantages: Declarative programming separates logic and implementation, such as filter, map and collect operations, making filtering, conversion and collection more intuitive; 2. Notes: Avoid modifying external variables in map or filter to prevent concurrency problems; 3. Operation classification: Intermediate operations (filter, map) are lazy to execute, and terminal operations (collect, forEach) are required to trigger execution, and terminal operations cannot be called multiple times; 4. Parallel flow: suitable for large data volumes and complex operations, but performance needs to be tested to avoid shared state operations.

Jul 05, 2025 am 02:23 AM

api

How to use lambda expressions in Java?

Lambda expressions were introduced in Java 8 to simplify the writing of functional interfaces. 1. Its basic syntax is (parameters)->{body}, and the parameter type or brackets can be omitted according to the situation. For example, if there is no parameter, use ()->System.out.println("Hello"), use x->System.out.println(x), use (x,y)->x y for multiple parameters; 2. The lambda can be assigned to functional interfaces such as Runnable, Consumer or Function, instead of anonymous class writing, and improve readability; 3. Often with sets and

Jul 05, 2025 am 02:22 AM

Effective Java Exception Handling Techniques

The key to handling Java exceptions is reasonable response rather than simple capture. First, do not ignore exceptions silently, at least print logs or retow; second, distinguish between recoverable and unrecoverable exceptions. The former uses checkedexception, and the latter uses uncheckedexception; third, avoid excessive use of try-catch, and problems that can be prevented should be checked in advance; finally, properly encapsulate custom exceptions to improve maintainability and context clarity.

Jul 05, 2025 am 02:13 AM

What are Java Records (Java 14 )?

JavaRecord is a feature used to simplify data class declarations, introduced from Java 14. It automatically generates constructors, getters, equals, hashCode and toString methods, which are suitable for DTO, model classes, multi-return value encapsulation and other scenarios; it is not suitable for situations where inheritance, mutable state or complex logic is required. Notes include: default is final class and fields, support for adding methods and static fields, and Java16 supports pattern matching. For example, recordPerson(Stringname,intage){} can replace the traditional POJO class and improve the simplicity and maintenance of the code.

Jul 05, 2025 am 01:58 AM

Java 14

How does HashMap collision resolution work in Java?

HashMap handles collisions mainly through chain storage. When multiple keys are mapped to the same index, they will be stored in the linked list or tree at that location. 1. HashMap uses hashCode() method to calculate the hash value of the key and determine the index in the array through internal logic; 2. When different keys produce the same index, they are linked to conflicting items in the form of a linked list; 3. If the length of the linked list exceeds 8, it will be automatically converted to a red and black tree to improve performance; 4. When the number of elements exceeds the product of the load factor and capacity, HashMap will double the capacity and reassign all entries, reducing the probability of collision but bringing certain performance overhead.

Jul 05, 2025 am 01:57 AM

How to create threads in Java programming?

There are two main ways to create threads in Java: inherit the Thread class and implement the Runnable interface. 1. To inherit the Thread class, you need to define a subclass and overwrite the run() method, and start a thread through start(), which is suitable for simple tasks but is limited by the Java single inheritance mechanism; 2. To implement the Runnable interface to separate tasks from threads, run Runnable instances through Thread, support more flexible design and can be used in combination with thread pools; in addition, Java8 can also use Lambda expressions to simplify the writing of one-time tasks. Be careful not to call run() directly, avoid repeated starts, reasonably naming threads, and understand the priority scheduling mechanism.

Jul 05, 2025 am 01:48 AM

java thread Thread creation

How does Java Garbage Collection work?

Garbage collection (GC) is the core mechanism of Java's automatic memory management, used to identify and free objects that are no longer in use to avoid memory leaks. 1. Garbage objects refer to objects that are no longer referenced by any root object; 2. The basic process of GC includes marking surviving objects and recycling unlabeled objects; 3. Common garbage collectors include SerialGC, ParallelScavenge, CMS, G1, ZGC/Shenandoah, which are suitable for different scenarios; 4. Methods to optimize GC performance include reasonably setting the heap size, selecting appropriate algorithms, monitoring logs, avoiding memory leaks, and reducing temporary object generation. By understanding the GC mechanism, code efficiency and system tuning capabilities can be improved.

Jul 05, 2025 am 01:43 AM

java Garbage collection

Preventing and Diagnosing Java Memory Leaks

To prevent and diagnose memory leaks in Java, the core method is "early detection and early processing". 1. First of all, you need to understand common scenarios: such as the static collection class not being released, the listener not being logged out, the cache not being invalidated, and the use of ThreadLocal improperly. 2. Secondly, use tools to assist detection, such as VisualVM preliminary positioning, MAT analysis heapdump, YourKit/JProfiler in-depth analysis, and JConsole observes memory trends. 3. In daily development, we should avoid long-term holding of useless objects, using weak references, using ThreadLocal reasonably and removing timely, logging out the listener after registration, unit test simulation to simulate long-term operation, and setting appropriate JVM parameters to enable GC logs

Jul 05, 2025 am 01:39 AM

How does Java Garbage Collection Work Internally?

Java's garbage collection mechanism manages memory by automatically identifying and cleaning up objects that are no longer in use. GC mainly operates in heap memory, divided into the new generation (including the Eden area and the Survivor area), the old age and the metaspace; common GC algorithms include mark-clear, copy and mark-collation, which are used to solve the memory recovery problems of different generations respectively; GC triggering timings include MinorGC (Eden area full time) and MajorGC/FullGC (when the old age is insufficient or when the System.gc() is called), explicit calls should be avoided; GC performance can be monitored and optimized through JVM parameters, logs and tools such as jstat, VisualVM, and MAT. Reasonable setting of the heap size and selecting the GC algorithm will help improve

Jul 05, 2025 am 01:29 AM

Understanding thread pools in Java ExecutorService.

Thread pools are the core mechanism used to manage threads in Java concurrent programming. Their role is to avoid the performance overhead caused by frequent creation and destruction of threads. 1. It improves response speed and resource utilization by pre-creating a set of threads and waiting for task allocation; 2. It is suitable for handling a large number of short life cycle and highly repetitive tasks, such as network requests or timing tasks; 3. Java provides a variety of thread pool types, including FixedThreadPool (suitable for heavy load systems), CachedThreadPool (suitable for short-term asynchronous tasks), SingleThreadExecutor (suitable for task serial execution) and ScheduledThreadPool (suitable for timing and periodicity)

Jul 05, 2025 am 01:21 AM

Thread Pool